
==== Front
Curr Res Microb Sci
Curr Res Microb Sci
Current Research in Microbial Sciences
2666-5174
Elsevier

S2666-5174(24)00048-8
10.1016/j.crmicr.2024.100266
100266
Articles from the special issue: Emerging Frontiers in Microbial-Mediated Utilization of Crop Residues for Economically Valuable Biomaterials, edited by Debasis Mitra,Periyasamy Panneerselvam, Govindan Selvakumar and Marika Pellegrini
Microbial biosurfactants: Green alternatives and sustainable solution for augmenting pesticide remediation and management of organic waste
Markam Shiv Shankar a1
Raj Aman b1
Kumar Ashwani ashwanikumar@allduniv.ac.in
c⁎
Khan Mohammed Latif a
a Forest Ecology and Ecosystems Laboratory, Department of Botany, Dr. Harisingh Gour Vishwavidyalaya (A Central University), Sagar, Madhya Pradesh, 470003, India
b Metagenomics and Secretomics Research Laboratory, Department of Botany, Dr. Harisingh Gour University (A Central University), Sagar, 470003, Madhya Pradesh, India
c Metagenomics and Secretomics Research Laboratory, Department of Botany, University of Allahabad (A Central University), Prayagraj, 211002, Uttar Pradesh, India
⁎ Corresponding author at: Metagenomics and Secretomics Research Laboratory, Department of Botany, University of Allahabad (A Central University), Prayagraj, 211002, Uttar Pradesh, India. ashwanikumar@allduniv.ac.in
1 Authors contributed equally.

13 8 2024
2024
13 8 2024
7 100266© 2024 The Authors. Published by Elsevier B.V.
2024

https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Highlights

• Microbial biosurfactants aid organic waste management, offering alternative substrates and promoting a circular economy approach.

• Recently biosurfactants have shown their potential in pesticide remediation.

• Some bacteria show their high biosurfactant production ability.

• This review focused on microbial biosurfactants as green solutions for environmental sustainability.

Pesticide pollution remains a significant environmental challenge, necessitating the exploration of sustainable alternatives. Biosurfactants are a class of unconventional surface-active chemicals that are produced by microorganisms. Biosurfactants have many applications in treating oil spills, emulsifiers, pharmaceuticals, and agriculture. Compared to chemical surfactants, they have benefits such as biodegradability, less toxicity, and a greener option because they are derived from microbes. Biosurfactants have recently been shown to have the potential to speed up pesticide cleanup. Biosurfactants are used in pesticide remediation because of their exceptional foaming ability, high selectivity, and wide range of pH, salinity, and temperature operating windows. Microbial biosurfactants emerged as potential agents for the treatment of organic waste and agricultural residue. This review unfolds the promising realm of microbial biosurfactants as green solutions for environmental sustainability, particularly in agricultural practices, with special reference to pesticide remediation. This article highlights the escalating need for eco-friendly alternatives, paving the way for discussing biosurfactants. Moreover, the articles discuss in detail various advancements in the field of rapid screening of biosurfactants, either using a conventional approach or via advanced instruments such as GC-MS, HPLC, NMR, FTIR, etc. Furthermore, the article unveils the molecular mechanisms and the microbial genes driving biosurfactant synthesis, offering insights into enhancing production efficiency. Moreover, the article explores diverse applications of microbial biosurfactants in sustainable agriculture, ranging from soil remediation to crop protection. The article also highlights the various functions of microbial biosurfactants for enhancing the decomposition and recycling of organic waste and agricultural residues, emphasizing their potential for sustainable waste management strategies. Overall, the review underscores the pivotal role of microbial biosurfactants as green alternatives for addressing pesticide pollution and advancing environmental sustainability.

Graphical abstract

Image, graphical abstract

Keywords

Pesticides
Remediation
Biosurfactant
Organic waste
Microbes
Sustainability
Microbial genes
==== Body
pmcIntroduction

Environmental pollution is one of the biggest issues facing the world today, endangering the health of millions of creatures on Earth and human health (Kumar et al., 2022a). One of the primary concerns associated with the expanding global population is the significant shift in land use paradigms worldwide. Several pressing environmental issues drive this shift, including climate change, environmental degradation, globalization, industrialization, and unsustainable development. These factors have collectively reduced the availability of resources for arable land, posing a substantial challenge to sustainable agricultural practices (Malla et al., 2022; Raj et al., 2021; Suhani et al., 2020). Soil erosion, natural and man-made disasters, soil pollution (fertilizers, pesticides, heavy metals, etc.), and inappropriate intensive farming practices are some of the leading causes influencing the deterioration of land resources (Mdeni et al., 2022). The latest projections from the United Nations indicate that the global population may reach approximately 8.5 billion by 2030 and 9.7 billion by 2050. The population is anticipated to peak at around 10.4 billion in the 2080s, maintaining this level to 2100. This surge in population will predominantly take place in developing nations (Source:https://www.un.org/development/desa/pd/sites/www.un.org.development.desa.pd/files/undesa_pd_2022_wpp_key-messages.pdf, Accessed on 08-03-2024). This increase in population will demand more agricultural productivity in declining land areas with a shift in climatic patterns, attracting different pests and thus affecting crop productivity. This increasing demand for crop output would be possible with extensive pesticide usage to meet the food demand of the expanding population (Raj et al., 2023).

The Food and Agriculture Organization (FAO) of the United Nations predicts that to meet the demands of a growing population, developing countries will need to boost their food production by 80%. This increase is expected primarily through higher crop yields and more frequent crop cycles on existing farmland. In contrast, only 20% of the additional food production is anticipated from expanding agricultural land (Source: https://www.fao.org/3/cc3017en/cc3017en.pdf, Accessed 8-03-2024). Projections for future food security are indeed cause for concern. Biotic stressors such as plant infections, diseases, pests, and weeds currently reduce agricultural productivity by 20–40 %, costing the global economy nearly US$ 290 billion annually (Tanda, 2022). To tackle the growing worldwide need for food, pesticides are essential in reducing crop production losses ascribed to insects and other pests (Raj et al., 2024a). The demand for agricultural systems to provide greater yields has increased due to population growth and shifting food habits. Crops are susceptible to serious damage from a range of pests without the strategic use of pesticides, which can result in major drops in both quantity and quality of yield (Chandran & Das, 2014; Singh & Gupta, 2018). Major food and cash crops in India lose between 15 and 20 % of their output due to pests (Kumar et al., 2020; Rathee & Dalal, 2018). A variety of solutions exist for managing pest and weed infestations, with most relying on chemical agents known as pesticides (particularly insecticides, weedicides, and herbicides). Pesticides are chemical substances, mixtures of substances, or agents (biological or manufactured) primarily used to eradicate pests (Lackmann et al., 2021). Globally, over 1,000 pesticides protect crops from pest damage and destruction.

Each pesticide possesses unique properties and toxicological effects tailored to address specific agricultural needs (Nwosu & John, 2022). Risk assessments for pesticide residues in food are carried out by an independent international expert scientific group, the Joint FAO/WHO meeting on pesticide residues. Among the pesticides evaluated, lindane, endosulfan, aldrin, metolachlor, and alachlor are of particular concern due to their high levels of residue (Source: https://www.fao.org/faostat/en/#data/QI, Accessed 08-03-2024) (Konstantinou et al., 2006). Among the Indian states, Punjab is leading in terms of pesticide consumption, followed by Maharashtra and Andhra Pradesh, while the consumption is much lower in North-eastern states like Assam, Manipur, and Nagaland. It must be noted that in many states, though the total consumption is medium, their rate for intensity of pesticide application is high, as seen in Jammu Kashmir and West Bengal (Fanda, 2019). According to a survey, organochlorine pesticides were the highest utilized in India because of their high-efficiency levels in controlling tropical pest populations. Insecticides were used in the highest amount when compared to herbicides or fungicides, and crops like cotton, wheat, and paddy demand high usage of these chemicals (Fanda, 2019).

Biosurfactants, a class of surface-active compounds produced by microorganisms, have garnered attention for their potential role in bioremediation processes. Chemical and biological surfactants are amphiphilic substances that can increase the solubility and mobility of hydrophobic or insoluble organic compounds by accumulating at the interface of immiscible fluids and reducing surface and interfacial tensions (Gupta et al., 2020). However, surfactants have varying effects on the hydrophobic contaminants' (pesticides, oil-spills, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, heavy metals, etc) bioavailability and biodegradation kinetics. Emulsifier effects on the bioremediation of pollutants can be either stimulating or inhibitory, depending on the chemical properties of the surfactant, pollutant, and microbe (Manga et al., 2021; Singh et al., 2007). Environment and health are very important in developed and developing countries. Therefore, the use of pesticides in the country is quite concerning in terms of the environment and health. Thus, evaluating pesticide use is necessary to understand the situation of pesticides in the country. Pesticides have significantly impacted the economy by preventing and reducing agricultural losses to pests and improving yield and the quality of the produce. Pesticide use in developing countries is increasing to achieve higher agricultural productivity and to enable farmers to reap the benefits of related agricultural investments. Microbial bioremediation has shown significant potential in mitigating a wide range of environmental pollutants, including pesticides and weeds (Azubuike et al., 2016; Mondal et al., 2024). The mechanisms by which biosurfactants facilitate the bioremediation of pesticides and weeds involve several key processes. Biosurfactants can increase the solubility and bioavailability of pesticides, making them more accessible to degrading microorganisms (Bilal & Iqbal, 2020).

Additionally, biosurfactants can emulsify and disperse pollutants, enhancing their contact with microbial cells and enzymes responsible for degradation (Bilal & Iqbal, 2020). Moreover, biosurfactants can act as a carbon source for microorganisms, providing them with the necessary nutrients to thrive and efficiently degrade the target contaminants. The ability of biosurfactants to solubilize and mobilize pesticides and weed-related compounds can also facilitate their removal from contaminated soils and water bodies (Azubuike et al., 2016; Bilal & Iqbal, 2020). Rhizobacteria that produce biosurfactants and exopolysaccharides have been reported to improve plant-assisted remediation of heavy metal-contaminated soil, providing a low-cost, environmentally benign, and long-term alternative to traditional remediation approaches (Lal et al., 2018; Kumar et al., 2022b). The handling of organic waste and agricultural leftovers is a significant challenge to sustainable agriculture and environmental preservation. Traditional approaches, such as composting and anaerobic digestion, are efficient but are sometimes hindered by the slow decomposition of complex organic compounds. Microbial biosurfactants, due to their distinct features, present a possible approach to improving these processes (Cerda et al., 2019; Eras-Muñoz et al., 2022). This review explores the recent developments in sustainable agriculture by exploring the role of microbial surfactants serving as greener alternatives to synthetic surfactants and offering enhanced potential for pesticide remediation by making these toxic compounds bioavailable for microbes. Furthermore, it gives a thorough review of the function of microbial biosurfactants in organic waste and crop residue management, emphasising their uses and potential advantages.

Biosurfactants: the next age compounds for sustainable agriculture

Biosurfactants, a diverse group of surface-active molecules produced by microorganisms, have gained significant attention due to their wide-ranging applications across various industries, including agriculture, bioremediation, pharmaceuticals, and cosmetics. These amphiphilic compounds exhibit unique properties such as emulsification, solubilization, wetting, and foaming, making them invaluable in various industrial, environmental, and biomedical applications. The growing global demand for sustainable and eco-friendly alternatives has intensified research efforts toward harnessing the potential of biosurfactants as green substitutes for synthetic surfactants derived from petrochemicals (Raj et al., 2021). The literature reveals that numerous bacteria from various genera, including Pseudomonas, Bacillus, Candida, Rhodococcus, and Corynebacterium, have been utilized for biosurfactant production, with Pseudomonas aeruginosa being recognized as one of the most potent biosurfactant producers (Martins & Martins, 2018). Given the substantial market demand for biosurfactants, biotechnological tools are harnessed to elucidate biosurfactant production pathways and identify strains or recombinant mutants with enhanced productivity. For instance, a novel mutant of S. bombicola has been engineered to produce various sophorolipids known as bola forms (Soetaert et al., 2013). These molecules feature two sophorose units flanking each side of the hydrophobic tail and exhibit extensive utility across various fields, including biomedicine for drug delivery, owing to their enhanced stability at higher pH levels (Van Renterghem et al., 2018).

Microorganisms can utilize diverse substances as carbon sources for biosurfactant production, with glucose and glycerol among the most common choices. However, the widespread use of glucose as an industrial feedstock and its dietary origin contribute to increased production costs associated with biosurfactant synthesis (Ogbonna et al., 2020). As an alternative, Wongsirichot et al. (2021) comprehensively analyzed the feedstocks employed for biosurfactant production. The use of complex substrates may result in contaminants in the final fermented extract. For example, Borah et al. (2019) reported numerous contaminants in the downstream phase of kerosene-based fermentation utilizing Serratia sp. for non-cytotoxic biosurfactant production. In some cases, yeast extract or macronutrients from various metal chloride, sulphate, or phosphate salts must be supplemented in biosurfactant synthesis media (Na, Mg, K, Ca, or Fe, among others).

Recent evidence suggests that the mineral fermentation medium serves as the primary fermentation medium in 40 % of the analyzed production instances, with slight variations in composition observed for each biosurfactant synthesis case. Furthermore, the exploration of utilizing inexpensive byproducts and waste as feedstock for sophorolipid manufacturing has been investigated due to the economic impact associated with using pure substrates and media supplementation (Ingham & Winterburn, 2022; Jiménez-Peñalver et al., 2020; Wang et al., 2018).

Types, physicochemical properties, and surface-active characteristics

Biosurfactants, also known as Microbial Surface-Active Compounds (MSAC), are amphiphilic molecules comprising hydrophobic and hydrophilic parts that facilitate the formation of interfaces between fluids with different polarities. Typically, the hydrophilic portion consists of amino acids, anionic or cationic peptides, and carbohydrates. Conversely, the hydrophobic tail generally comprises peptides, proteins, or fatty acids, which can be either saturated or unsaturated (da Rocha Junior et al., 2019; Farias et al., 2021). The ability of MSAC to reduce interfacial tension varies depending on its chemical structure. MSACs can be categorized into two principal groups based on their molecular weight: low molecular weight (such as glycolipids and lipopeptides) and high molecular weight (including polysaccharides, lipopolysaccharides, proteins, and lipoproteins). Low-molecular-weight biosurfactants exhibit greater effectiveness in reducing surface tension, whereas high-molecular-weight biosurfactants are more adept at stabilizing oil-water emulsions (Femina Carolin et al., 2020; Jiménez-Peñalver et al., 2019; Karlapudi et al., 2021). The chemical disparities in the molecular structure of various biosurfactants are directly linked to their biological activities and applications (Morita et al., 2015).

Low-molecular-weight biosurfactants are widely utilized in environmental applications. Among these, glycolipids are particularly notable, encompassing trehalolipids, mannosyl erythritol lipids (MELs), rhamnolipids, and sophorolipids (Sharma et al., 2021). Trehalolipids consist of trehalose disaccharides linked to fatty acids, primarily mycolic acids, via α-1-glycosidic bonds and are associated with species such as Mycobacterium, Corynebacterium, and Nocardia (Rodrigues & Teixeira, 2010; Varjani & Upasani, 2016). MELs are produced by microorganisms of the genera Pseudozyma and Ustilaginaceae (Beck & Zibek, 2020).

Rhamnolipids, first described as biosurfactants, are mainly produced by Pseudomonas aeruginosa (Edwards & Hayashi, 1965). They consists of mono- and disaccharides of rhamnose linked by glycolic bonds to β-hydroxy fatty acid molecules (Chong and Li, 2017). Rhamnolipids are used extensively in oil recovery processes and are applied in agriculture for plant pathogen control and soil quality improvement (Patowary et al., 2016). Rhamnolipids are very effective in reducing surface tension. They can lower the surface tension of water from 72 mN/m to about 25–30 mN/m. Rhamnolipid from Lysinibacillus sphaericus lowered surface tension from 72 N/m to 52 N/m, improving hydrophobic pesticide dissolution (Gaur et al., 2019). Due to their strong surface-active properties, they are widely used in bioremediation, enhanced oil recovery, and as emulsifiers in various industries (Varjani et al., 2021). Rhamnolipids biosynthesis takes place via the biofilm formation pathway in Pseudomonas aeruginosa. The main key factors relevant in the regulation of biofilm formation by Pseudomonas aeruginosa include cAMP/Vfr signalling, quorum sensing (QS) systems, Gac/Rsm pathway, and c-di-GMP signaling (Fig. 1).Fig. 1 KEGG pathway for rhamnolipid biosynthesis via Pseudomonas aeruginosa.

Fig 1

Sophorolipids, discovered in the early 1960s, are primarily produced by Starmerella bombicola strains (Jiménez-Peñalver et al., 2019; Tudi et al., 2021). They exhibit structural variations, including cyclic or acyclic forms, sophorolipid sugar modifications (lactonization or acetylation), and fatty acid lengths (16 or 18 carbon atoms) with varying degrees of saturation (Callaghan et al., 2016). Sophorolipid synthesis occurs through the fatty acid degradation pathway (Fig. 2.) Studies have indicated the potential of sophorolipids to be derived from water-insoluble substrates such as organic waste, aligning with circular economy principles and offering promising industrial applications (Gaur et al., 2019a). Candida bombicola yeast produces sophorolipids that can solubilize non-aqueous phase liquids, as well as stability and emulsifying activity against organic solvents and oils, making them promising for environmental applications (Daverey and Pakshirajan, 2010). Sophorolipids can also significantly reduce surface tension, typically lowering it to around 30–40 mN/m (Xu et al., 2019). They are widely used in personal care products, detergents, and antimicrobial agents.Fig. 2 Synthesis of sophorolipid via fatty acid degradation pathway generated via KEGG database.

Fig 2

Surfactin, is another highly potent biosurfactant composed of cyclic lipopeptides. Its structure includes a ring of seven amino acids linked to a fatty acid chain through a lactone bond. This unique configuration enhances its surface-active properties, making Surfactin extremely effective in reducing surface and interfacial tension. Surfactin has been widely studied for its applications and is known for its antimicrobial, antiviral, and anti-inflammatory properties. Its effectiveness extends to environmental and industrial applications, including oil spill remediation and enhanced oil recovery, due to its ability to emulsify hydrocarbons. Its biocompatibility and biodegradability make it an attractive alternative to synthetic surfactants (Meena et al., 2021). While all (rhamnolipids, sophorolipids and surfactin) are effective biosurfactants, rhamnolipids tend to have a slightly more remarkable ability to reduce surface tension as compared to the others (Varjani et al., 2021; Saiyam et al., 2024). Fig. 3. shows the structure of various microbial surfactants.Fig. 3 Types of microbial surfactants.

Fig 3

Conventional screening methods for microbial biosurfactant production

Different approaches have been in use for a long time to detect the production of biosurfactants from a diversity of microbes. Some of these methods are as follows:

Measurement of surface tension /interfacial measurement

The most efficient and reliable method for screening microorganisms for biosurfactant production (Adetunji & Olaniran, 2021). Surface tension, which measures free energy per unit area at an interface or surface, is a critical parameter in biosurfactant evaluation (Walter et al., 2010). Distilled water (DW) typically exhibits a surface tension of 72 mN/m. However, upon the addition of biosurfactants, the surface tension of DW decreases. The effectiveness of biosurfactants is determined by their ability to reduce the surface tension of DW to less than 40 mN/m. For instance, a rhamnolipid biosurfactant produced by Pseudomonas aeruginosa was found to reduce the surface tension of water to approximately 30 mN/m (Adetunji & Olaniran, 2021; Dusane et al., 2010; Geetha et al., 2018).

Oil spreading technique

In a petri dish, 100 µl of oil is poured onto 50 ml of distilled water, and 100 µl of cultured supernatant is placed in the middle of the oil layer (Nwaguma et al., 2016). The oil displacement and the clean zone's appearance indicate the presence of surfactant in the culture supernatant. The diameter of the clean zone on the surface of the oil correlates inversely with surfactant activity (Adetunji & Olaniran, 2021). The oil-spreading approach represents a quick, precise, and reliable method for identifying bacteria that synthesize biosurfactants (Hazra et al., 2011; Walter et al., 2010).

Penetration assay

The basis of this assay lies in the colour change that occurs when two insoluble phases mix. In this experiment, 150 µl of a hydrophobic paste, consisting of oil and silica gel, is dispensed into each of the 96 wells of a microplate. Subsequently, 10 µl of oil is layered over the paste. The culture's supernatant is then coloured by combining 90 µl of supernatant with 10 µl of a red staining solution. The coloured supernatant is applied to the surface of the paste. The hydrophilic liquid will breach the oil film barrier and permeate the paste if a biosurfactant is present. Within 15 min, the silica will transition from a distinct red hue to a hazy white as it enters the hydrophilic phase (Singh & Sedhuraman, 2015; Touseef et al., 2018; Walter et al., 2018).

Emulsification index

The emulsification index, denoted as E24%, quantified emulsification activity (Nwaguma et al., 2016). This measure, expressed as a percentage, represents the total height of the emulsion divided by the height of the aqueous layer multiplied by 100. It offers a straightforward and replicable method for assessing emulsifying activity based on the ability of biosurfactants/bio emulsifiers (BS/BE) to generate stable emulsions when mixed with n-heptane.

A recent study by Tavares et al. (2021) introduced a rapid and reproducible technique to determine emulsifying activity. This method involves adding 1 mL of n-heptane to 1 mL of an aqueous solution containing the surfactant/cell-free culture broth in a 4 mL screw cap glass tube (10 ×75 mm, ND10 caps with PTFE septum). After vortexing for 2 min, the tube is allowed to stand upright for 10 min before analysis. This process is repeated until the organic phase is completely emulsified, using increasing quantities of surfactant/cell-free culture broth. The volume of product (Volmin of emulsifier/surfactant), up to 1 mL, required to create and maintain a 100 % emulsion in the organic phase is defined as one emulsifying unit, or 1 U. The emulsifying activity (EA) is then calculated as EA= 1 U/Volmin (mL), providing a measurement in U/mL (Tavares et al., 2021). This methodology directly compares different chemicals with surfactant properties, offering swift assessments of substances derived from various chemical and biological sources.

Foaming activity

One can investigate foam formation resulting from biosurfactant activity by agitating the supernatant collected in a test tube. The presence of biosurfactants in the supernatant is confirmed in the event of foam formation. The following formula can be used to quantify foaming activity quantitatively:Foaming = (height of foam / total height of supernatant) × 100

This action also gauges how well biosurfactants are reducing surface tension (Bader et al., 2021; El-Sheshtawy et al., 2016).

Blood hemolysis test

The organisms were inoculated onto blood agar plates and examined for hemolysis following incubation. Blood agar plates were prepared by adding 5 ml of sheep blood to 1 L of nutritional agar medium. Freshly formed colonies were streaked onto these plates and cultured for 72 h at 30 °C. The presence of a clear zone or greenish tint surrounding the colonies (α- or β- hemolysis) indicates the potential of the bacterial isolate to produce biosurfactants (Ibrahim et al., 2013; Thavasi et al., 2010). While hemolytic activity has been considered an unreliable criterion for detecting biosurfactant (BS) activity (Satpute et al., 2008), assessing the BS productivity of a culture directly on agar under various conditions remains highly challenging (Youssef et al., 2004). Though widely recognized as the optimal technique for detecting rhamnolipids and surfactins, the haemolytic activity of biosurfactants has certain drawbacks, including the creation of clear zones surrounding bacterial colonies due to the activity of other lytic enzymes, little to no support for hydrophobic substrates, and difficulties in producing biosurfactants because of diffusion restriction, which subsequently inhibits the formation of clear zones (Eldin et al., 2019).

Drop collapse test

After one hour, the results were evaluated after applying 0.01 ml of the culture supernatant onto sterile glass slides treated with oil. The extent of the decrease varies depending on the concentration of the crude biosurfactant (Karamchandani et al., 2022). The displacement of oil and the emergence of a clean zone indicate the presence of surfactant in the culture supernatant. The diameter of the clean zone on the oil surface correlates inversely with surfactant activity (Adetunji & Olaniran, 2021; Sarwar et al., 2018).

Detection of anionic biosurfactant- blue agar plate (BAP) method

To detect anionic biosurfactants, mineral salt agar media was prepared with glucose as a carbon source (2 %), cetyltrimethylammonium ammonium bromide (CTAB: 0.5mg/ml), and methylene blue (MB: 0.2 mg/ml) (Satpute et al., 2008). Wells were filled with 30µl of the cell-free supernatant and prepared in a methylene blue agar plate. The plate was then incubated at 37°C for 48–72 hours. A dark blue halo around the culture indicated the production of anionic biosurfactants.

Phenol-sulphuric acid method

The strains were inoculated with Bushnell Haas Broth (BHB) and cultured for 4–5 days at 37 °C on a rotating shaker. Following incubation, the broth was centrifuged for 15 min at 10,000 rpm. Next, 5 ml of concentrated H2SO4 was added dropwise after combining 1 ml of the collected supernatant with 1 ml of 5 % phenol. The presence of biosurfactant was indicated by the appearance of an orange hue (Patel & Patel, 2020).

Bacterial adhesion to hydrocarbons (BATH) assay

Bacterial cells were suspended in a phosphate buffer salt solution after two washes to attain an optical density (OD) of 0.5 at 600 nm. A 2 ml cell solution was mixed with 100 µl of crude oil and vortexed for three minutes. After allowing one hour for the crude oil and aqueous phase to separate, the OD of the aqueous phase was measured at 610 nm (Huang et al., 2020). From these OD values, the percentage of cells attached to crude oil was calculated using the following formula:

% of bacterial cell adherence = {1 - (OD shaken with oil / OD original)} × 100 (Raj et al., 2021).

CTAB agar plate method

A semi-quantitative screening technique, CTAB (cetyltrimethylammonium bromide) agar plate, can detect extracellular glycolipids or other anionic surfactants (Hazra et al., 2011). Developed by Siegmund & Wagner (1991), this CTAB agar method facilitates the identification of bacteria synthesizing biosurfactants. Target microorganisms are cultured on agar plates containing light blue mineral salt, the cationic surfactant CTAB, and the basic dye methylene blue. Upon release of anionic surfactants by the microorganisms onto the plate, an insoluble dark blue ion pair forms when they react with CTAB and methylene blue (Rajesh et al., 2017). Consequently, bacteria-producing surfactants are encircled by dark blue halos (Adetunji & Olaniran, 2021). This approach is straightforward, selective for anionic surfactants, and adaptable to various substrates and temperatures, including liquid broth or agar plates. However, CTAB is toxic and inhibits the growth of numerous bacterial colonies (Walter et al., 2010).

Surface tension

The critical micellization concentration (CMC) value indicates the surfactant's efficacy and efficiency in measuring surface and interfacial tension (Koim-Puchowska et al., 2019). There were several ways to measure surface tension, including the capillary rise method. The supernatant was moved to glass tubes and submerged using the capillary rise technique in a water bath. To determine surface tension, a standardized capillary tube was submerged in each glass tube, and the height that the supernatant reached was estimated as an action of free ascending force. The equation; γ = r × h × d × g2 can be used to calculate surface tension, where surface tension (mNm−1) is denoted by ‘γ’, capillary radius (cm) by ‘r’, height of the liquid column (cm) by ‘h’, density (g/ml) by ‘d’ and gravity by ‘g’ (Eldin et al., 2019). Additionally, tensiometers can be used to measure the surface tension of cell-free culture broth using various techniques, including the Du Nouy Ring approach (Nayarisseri et al., 2018).

Victoria Pure Blue BO assay

This assay relies on the interaction between biosurfactants and Victoria Pure Blue BO dye. Biosurfactants, when present, interact with the dye, resulting in a change in colour or absorbance, which can be measured spectrophotometrically. This change in colour or absorbance indicates the presence and concentration of biosurfactants in a given sample. Biosurfactants in culture supernatant can be screened using Victoria Pure Blue BO (VPBO) dye, as described by Sohail & Jamil (2023). This colorimetric assay quantifies biosurfactant concentration and identifies various anionic and non-ionic biosurfactants. The solubility of VPBO depends on the presence of detergents. When biosurfactants are present in the sample or supernatant, micelle formation occurs, solubilizing the immobilized dye and enhancing the specific absorption of VPBO. This relationship is represented by a logarithmic linear curve.

Conversely, if no biosurfactants are present, VPBO remains insoluble, and its specific absorption does not change (Roosloot & Schoen, 2011). When employing this technique for biosurfactant screening, it was recommended to operate within a pH range that facilitated the solubilization of biosurfactant micelle production (Kubicki et al., 2020). The Victoria Pure Blue BO assay is often used in research and industrial applications to assess the production of biosurfactants by microorganisms or to evaluate the efficiency of biosurfactant production processes (Roosloot & Schoen, 2011).

Bromothymol blue assay

Bromothymol blue (BTB) was dissolved in phosphate-buffered saline (0.2 M Na2HPO4, 0.2 M NaH2PO4, and 1 M NaCl) to create a BTB solution (0.2 mM), which was then pH-adjusted to 7.2. Unless stated otherwise, the assay is conducted in 96-well plates using equal volumes of BTB and surfactant samples. A 96-well plate reader measures the quantitative response at 616 nm and 410 nm wavelengths. The colourimetric response (CR, %) is quantified (Satake et al., 1960). Blanks for the samples are created by mixing BTB with the media in which the samples are dissolved. Due to the assay's sensitivity to pH fluctuations, the samples were adjusted to pH 7-8 before testing (Ong & Wu, 2018). Table 1 shows the use of various conventional methods to detect biosurfactants.Table 1 Detection of biosurfactants via advanced analytical tools, screening methods used and the type of biosurfactant produced.

Table 1S. No.	Biosurfactant producing bacteria	Detection assay	Analyzed via	Surfactant name	Application	Reference	
1.	Bacillus atrophaeus 5-2a	Oil spreading	Fourier transform infrared spectroscopy (FT-IR)	Lipopeptide	Microbial enhanced oil
recovery	(Zhang et al., 2016)	
2.	Bacillus licheniformis	foaming, emulsifying,	PCR method	Lichenysin	Microbial enhanced oil recovery in-situ application.	(Karlapudi et al., 2018)	
3.	Acinetobacter
calcoaceticus	Microbial enhanced oil recovery (MEOR)	Nuclear Magnetic Resonance (NMR) spectroscopic	Emulsion Glycolipopeptide	Microbially enhanced oil
recovery	(Karlapudi et al., 2018)	
4.	Bacillus coagulans	Foaming agents, emulsifiers and dispersing agents	Nuclear Magnetic Resonance (NMR) spectroscopic	Surfactin	Increases the recovery of
oil	(Karlapudi et al., 2018)	
5.	Bacillus subtilis		HPLC system	Surfactin	Increases the recovery of
oil	(Barros et al., 2013)	
6.	Halomonas species	CTAB Agar Plate Method	High performance liquid chromatography (HPLC)	Glycolipid	Remediation of spilled
Oil in marine ecosystems.	(Hazra et al., 2011)	
7.	Marinobacter
hydrocarbonoclasticus	Biofilm formation	High performance liquid chromatography mass spectrometry (HPLC–MS)	Phospholipopeptide	Crude oil solubilization	(Tripathi et al., 2018)	
8.	Rhodococcus soli	Oil displacement test	Liquid chromatography–tandem mass spectrometry (LC-MS/MS)	Rhamnolipid	Bioremediation of crude
oil from the contaminated
environment	(Lee et al., 2018)	
9.	Pseudomonas aeruginosa	Measurement of Surface Tension	Quantitative reverse transcription-PCR	Rhamnolipid	Efficiency for heavy metal removal such as
mercury and lead	(Adetunji & Olaniran, 2021)	
10.	Pseudomonas species	Measurement of Surface Tension /Interfacial Measurement	Quantitative reverse transcription-PCR	Rhamnolipid	Biodegradation of hydrocarbons	(Karlapudi et al., 2018)	
11.	Acinetobacter venetianus	Oil emulsion	HPLC system	Emulsan	Removal of crude oil from the marine
environment	(Karlapudi et al., 2018)	
12.	Candida albicans	Microbial enhanced oil recovery (MEOR)	FTIR analysis	Sophorolipid	Microbial enhanced oil
recovery	(El-Sheshtawy et al., 2016)	
13.	Bacillus nealsonii S2MT	Emulsifying	Transmitted Electron Microscopy (TEM) and 16S rRNA ribo-typing	Surfactin	Reduction in the
pollution level of 10 %
heavy engine oil
contaminated soil	(Phulpoto et al., 2020)	
14.	Bacillus subtilis	-	-	Surfactin	Removal of heavy metals
and petroleum
hydrocarbons	(Singh & Cameotra, 2013)	
15.	Bacillus subtilis	Emulsifying	Transmitted Electron microscopy (TEM) and 16S rRNA ribo-typing	Surfactin	Remediation of diesel oil
contaminated soil	(Phulpoto et al., 2020)	
16.	P. aeruginosa BS2	-	Inductively Coupled Plasma Atomic Emission Spectrophotometer (ICP-AES)	Rhamnolipid	Removal of heavy metals
such as cadmium and
nickel	(Juwarkar et al., 2008)	
17.	Bacillus subtilis	Surface tension	HPLC	Lipopeptide	Enhancement in oil
recovery and
remediation of soil
Contaminated soil.	(Mulligan, 2021)	
18.	Burkholderiacepacia	-	Gas chromatograph (GC)	Saponin	Desorption of Copper
and nickel from kaolin	(Mulligan, 2021)	
19.	Stenotrophomonas
maltophilia	Drop collapse assay	Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR)	Rhamnolipid	Removal of crude oil	(Tripathi et al., 2020)	
20.	Lysinibacillus sphaericus	Hemolysis of blood	Ultra Performance Liquid Chromatography (UPLC)	Rhamnolipid	Solubilization of
hexachlorocyclohexane	(Gaur et al., 2019b)	

Optical distortion grid assay

When surfactant was added, the smooth surface of pure water in a well became concave, causing the edges of the well to become wet. Observing from above, the fluid formed a single diverging lens, creating a grid-like distortion of images. A microwell titer plate was used to study the optical distortion caused by biosurfactant-containing supernatant. Grids of black and white were placed on a backing sheet of paper, and the plate was observed through this grid paper after the supernatant was added to the wells. The presence of biosurfactant caused noticeable optical distortion, which indicated a positive test outcome. This method effectively demonstrated the ability of biosurfactants to alter surface tension and optical properties, providing a visual confirmation of their presence and activity in the solution. Such observations are crucial for understanding how biosurfactants interact with their environment and can be utilized in various applications, including bioremediation and industrial processes (Hussain & Khan, 2018).

Advanced analytical methods for microbial surfactant identification

Microbial surfactants have received a lot of interest because of their wide range of uses, from bioremediation to pharmaceuticals. Accurate identification of these chemicals is critical for understanding their characteristics and maximizing their use. Microbial surfactant identification uses a variety of analytical techniques, including Gas Chromatography-Mass Spectrometry (GC-MS), Nuclear Magnetic Resonance (NMR) spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), High-Performance Liquid Chromatography (HPLC), and so on (Raj et al., 2024b).

The composition and possible uses of a biosurfactant generated by Pseudomonas aeruginosa and Pseudomonas guguanensis strain Iraqi ZG.K.M. have been identified by GC-MS analysis, which showed the presence of fatty acids, rhamnolipids, and other hydrophobic substances (Faisal et al., 2023). Microbiological surfactant characterization has made considerable use of NMR. For instance, lipid and sugar moieties of a biosurfactant generated by Bacillus subtilis were discovered by NMR analysis, confirming the glycolipid composition of the compound and other structural elements essential to surfactant action (Mnif et al., 2021; Sharma et al., 2022). A biosurfactant made by Candida tropicalis was subjected to FTIR analysis, which provided information on its molecular structure and possible uses in emulsification and oil recovery. The peaks identified by the study corresponded to ester, alcohol, and carboxylic acid groups (Almeida et al., 2021). XRD is utilized to ascertain a material's crystalline structure and phase composition. XRD can offer information about the physical state and molecular structure of surfactant molecules, however, it is not as frequently employed for microbial surfactant investigation. An X-ray diffraction (XRD) examination of a biosurfactant isolated from Streptomyces species revealed that it was amorphous, indicating that it might be used in applications that needed surface activity and flexible film production (Javee et al., 2020). Process optimisation and quality control in industrial applications were made easier by measuring a biosurfactant's primary components using HPLC analysis of a biosurfactant generated by Candida lipolytica (Rufino et al., 2014). Each tool has its merits and demerits and by harnessing these analytical tools, researchers can unlock the full potential of microbial surfactants for various biotechnological and industrial applications. Table 1 displays various techniques used for rapid detection and identification of biosurfactants.

Microbial genes driving biosurfactant production

It is essential to comprehend the genetic underpinnings of their synthesis to maximise the production of biosurfactants and investigate their potential in sustainable solutions. The biosurfactants' synthesis is encoded by many regulated microbial genes, which can be used in genetic engineering techniques to increase biosurfactant outputs. Several bacterial genes are essential for the synthesis of biosurfactants. These genes encode biosynthesis-related enzymes, transporters that export biosurfactants, and regulatory proteins that regulate gene expression. The lipopeptide biosurfactant surfactin is synthesised by enzymes encoded by the srf genes (srfA, srfB, srfC, and srfD) present in Bacillus species (Qiao et al., 2024). The Pseudomonas aeruginosa rhl genes (rhlA, rhlB, and rhlC) encode the enzymes needed to biosynthesize rhamnolipids, a type of glycolipid biosurfactants (Reis et al., 2011). Several microbial species, including Rhodococcus and Candida, encode mls genes (mlsA, mlsB, and mlsC), which are involved in the production of mannosyl erythritol lipids (MELs), a class of glycolipid biosurfactants (Soccol et al., 2022). The three cel genes (celA, celB, and celC) that are present in some bacteria, such as Pseudomonas and Burkholderia, code for the enzymes needed to produce cellobiose lipids, which are another class of glycolipid biosurfactants (Zibek et al., 2022). Numerous regulatory genes exist, including rhlR and rhlI. They encode a quorum-sensing mechanism in Pseudomonas aeruginosa that controls the expression of rhl genes involved in manufacturing rhamnolipids (Pearson et al., 1997). ComA, a transcriptional regulator that regulates the expression of srf genes, is present in Bacillus species (Qiao et al., 2024). While the transporter gene rhlE, expressed by Pseudomonas, controls an efflux pump involved in rhamnolipid secretion, transporter gene bapA, produced by Bacillus subtilis, oversees exporting surfactin from the cell membrane into the extracellular environment (Tursi and Tükel, 2018; Cosson et al., 2002). These are only a few instances of the bacterial genes involved in synthesising biosurfactants; specific genes will differ based on the kind of biosurfactant produced and the species of microbes involved. Genetic engineering techniques targeted at improving biosurfactant yields, changing biosurfactant characteristics, and streamlining biosurfactant production processes require an understanding of the genetic framework of biosurfactant production. It will assist in using a cutting-edge CRISPR-based strategy to introduce the genes needed for biosurfactant synthesis into native microorganisms for the sustainability of the environment. Table 2 displays various microbial genes responsible for the synthesis of biosurfactants.Table 2 Biosurfactant-producing microorganisms, genes involved and types of biosurfactant produced

Table 2:S.No.	Biosurfactant producing microorganism	Genes	Analyzed via	Biosurfactant name	Biosurfactant produce	Application	References	
1.	Bacillus
amyloliquefaciens
LL3	srfA operon	HPLC–MS analysis	Surfactin	-	Food processing, pharmaceuticals, oil recovery, and environmental governance	(Zang et al., 2021)	
2.	Ustilago maydis	acyltransferase
Mac1and Mac2
gene	High-performance liquid chromatography (HPLC)	Mannosylerythritol
lipids	-	Metabolic engineering of extracellular glycolipids.	(Becker et al., 2021)	
3.	Bacillus subtilis
strain 168	sfp gene and
biofilm pathway
respectively	QRT-PCR	Surfactin	12.8 g/L	The synthesis of surfactin	(Wu et al., 2019)	
4.	B. subtilis
(pHT43-comXphrC)	ComX and PhrC	Fourier transform infrared spectroscopy (FTIR)	Surfactin	140.2 mg/L surfactin	Natural substrates and nutrient cycling	(Jung et al., 2012)	
5.	Bacillus subtilis	PsrfA with Pg3	Transcriptomic analysis	Surfactin	9.74 g/L	Useful for surfactin production	(Jiao et al., 2017)	
6.	Starmerella
bombicola	Lactone esterase
(rSBLE)	Perform HPLC and liquid chromatography-mass spectrometry (LCMS)-based assays	Sophorolipids	0.75 mg/l	Usage in the industry	(Ciesielska et al., 2016)	
7.	Candida bombicola	PHAC1co and
UGT1co	High-Performance Liquid Chromatography (HPLC)	Cellobioselipid and
simultaneous poly-hydroalkan	400 g/L	Genetic engineering	(Soetaert et al., 2013)	
8.	Pseudomonas aeruginosa	rhl gene cluster (rhlA, rhlB, rhlR, and rhll)	Quantitative reverse transcription-PCR	Rhamnolipid	-		(Wittgens & Rosenau, 2018)	
9.	Bacillus subtilis 168	srfAA-AD	High-performance thin-layer chromatography (HPTLC)	Plipastatin	17 mg/L		(Vahidinasab et al., 2020)	
10.	Bacillus subtilis I68	ppsABCDE	High Performance Liquid Chromatography (HPLC)	Fengycin/ Plipastatin	15 mg/L		(Vahidinasab et al., 2020)	
11.	Acinetobacter lwoffii RAG-1	wee	Thin-layer chromatography (TLC)	Emulsan	-		(Wittgens & Rosenau, 2018)	
12.	Bacillus subtilis
RB14	ituD	HPLC	Iturin A	32.86 mg/L	Industrial production	(Geissler et al., 2019; Xu et al., 2020)	
13.	Ustilago maydis	Emt1, Mmc1,
Mac1, Mac2	High-performance liquid chromatography (HPLC)
thin-layer chromatography (TLC)	Mannosylerythritol
Lipids	-	Economic use of this renewable resource	(Becker et al., 2021)
(Saika et al., 2018)	
14.	Pseudomonas
fluorescens SS101	massA, massB,
and massC	Quantitative real-time PCR analysis	Massetolide	-	Biofilm formation	(De Bruijn & Raaijmakers, 2009)	
15.	Bacillus licheniformis JF2	licA, licB and
licC	PCR method	Lichenysin	-	Biosurfactant industry	(Das et al., 2008; Geissler et al., 2019)	
16.	Pseudomonas
fluorescens
SBW25	LuxR-type
transcriptional
regulators	HPLC and liquid chromatography-tandem mass spectrometry (LC-MS/MS)	Viscosin	-	-	(De Bruijn & Raaijmakers, 2009)	
17.	Starmerella
bombicola
(Candida)	cyp52M1,
ugtA1, ugtB1
and mdr	Gas–Liquid Chromatography	Sophorolipid	40 g/L	Gene sequence analysis in yeast taxonomy	(Kurtzman et al., 2010)	
18.	Pseudozyma
flocculosa	Cyp, fgt, fas, fat,
fhd, atr and rfl	LC-MS analysis	Cellobioselipids	-	Protein identification based on homology	(Teichmann et al., 2011)	
19.	Serratia
marcescens	swrW gene	RT-PCR analysis	Serrawettin	-	Infected tissues or ex vivo environments	(Thies et al., 2014)	
20.	Dietzia maris As-13–3	tetR, fd, fdR,
acdH, addH,
and acS	Gas Chromatography-Mass Spectrometry (GC-MS), quantitative real-time PCR (Q-PCR)	Di-rhamnolipid	-	Oil degradation and marine oil removal	(Wang et al., 2014)	
21.	Starmerella bombicola	sble	Gas Chromatography-Mass Spectrometry (GC-MS)	Lactone Esterase)	-	Marine oil removal	(Wang et al., 2018)	
22.	Haloarchaea	Metagenomic
gene fra	genomic DNA,	Metagenomic
biosurfactant
protein 1 (MBSP1)	-	Green surfactants market, deep benthic ecosystems	(Farias et al., 2021)	

Applications of microbial biosurfactants in sustainable agriculture

Agricultural utilization of biosurfactants

Surfactants serve as mobilizing agents, enhancing the solubility of bio-hazardous chemical substances such as polycyclic aromatic hydrocarbons (PAHs), thereby improving the apparent solubility of hydrophobic organic contaminants (HOC) (Makkar & Rockne, 2003). Additionally, they play a crucial role in reducing the diffusion distance between the absorption site and microbial uptake by aiding in the adhesion of microbes to soil particles containing contaminants (Makkar & Rockne, 2003). In agriculture, surfactants are utilized to hydrophilize heavy soils, improving wettability and ensuring even distribution of fertilizers. Moreover, they facilitate the distribution and penetration of toxicants in pesticides while preventing fertilizer caking during storage (Makkar & Rockne, 2003). The rhamnolipid biosurfactant, predominantly produced by the genus Pseudomonas, exhibits potent antibacterial activity, with no adverse effects expected on human health or the environment upon cumulative exposure (Makkar & Rockne, 2003). Fengycins, another class of biosurfactants, demonstrate potential for biocontrol of plant diseases due to their reported antifungal properties (Traudel & Merten, 2018).

Biosurfactants as biopesticides

Weeds, bacterial and fungal infections, flies, rats, nematodes, and insects represent pests capable of impacting crop yields, cultivation, and overall health. Surfactants, utilized as adjuvants to enhance the efficacy of insecticides, possess significant structural characteristics (Adetunji & Olaniran, 2021). However, frequent usage substantially negatively impacts human, environmental, and soil health. The hazardous, persistent, resistant, and prolonged half-life characteristics contribute to this predicament. Consequently, scientists and researchers face challenges in devising environmentally benign methods to mitigate such damage and environmental stress. Green chemistry emerges as a potential solution, offering avenues for developing eco-friendly technologies and yielding precious products. Microbially-produced secondary metabolites are widely recognized for their beneficial effects on soil and plant health, including their ability to inhibit pest growth and solubilize insoluble substances (Akbari et al., 2018; Chopra et al., 2020; Karamchandani et al., 2022).

Conventional arthropod control strategies often entail the application of broad-spectrum chemicals and pesticides, leading to undesirable effects. Moreover, the emergence of pesticide-resistant insect populations and escalating prices of new chemical pesticides have spurred the quest for novel eco-friendly vector control measures. Lipopeptide biosurfactants, synthesized by various bacteria, exhibit insecticidal activity against the fruit fly Drosophila melanogaster, thus holding promise as biopesticides (Belén Moldes et al., 2019).

Biosurfactants for phytoremediation

Phytoremediation emerges as a method for remediation of metal-contaminated soil, although plants often accumulate metals without fully absorbing them, posing risks of biomagnification throughout the food chain (André et al., 2007). However, biosurfactants have gained prominence in phytoremediation endeavours by fostering plant growth and improving soil quality. Specifically, treating metal-contaminated plants with biosurfactants promotes proper cell division or germination during growth phases (Singh et al., 2019). In recent studies, Shah and Daverey (2021) observed increased sophorolipids within Cd-contaminated soils. The application of biosurfactants reduced proline levels in Bidens pilosa, a metal-accumulating plant, with levels declining from 40.2 moles per gram in the control group to 18.2 moles per gram in the treated soil. Moreover, the adverse effects of Cd were significantly mitigated. Sophorolipids also enhanced root permeability and shoot and root growth of Medicago sativa and B. pilosa, consequently augmenting phytobiomass and nutrient uptake.

Given their binding capabilities, biosurfactants play a crucial role in forming complex biosurfactant-metal structures via various attraction or repulsion forces. This suggests their potential as alternatives to persistent chelating chemicals. Incorporating biosurfactant augmentation into phytoremediation strategies holds promise for reducing metal toxicity and enhancing plant growth. Furthermore, ongoing research unfolds plant utilization of biosurfactants and their mechanisms of stress defence (Eras-Muñoz et al., 2022).

Biosurfactants' usage in the environment

The solubility of hydrophobic organic pollutants often presents a barrier to their biodegradation. Biosurfactants, due to their ability to mobilize, emulsify, and solubilize these chemicals, have emerged as a well-researched strategy for enhancing biodegradation processes in wastewater treatment and soil bioremediation (Karamchandani et al., 2022). By reducing capillary forces that impede pollutant movement, biosurfactants improve the interaction between water and the oil-solid matrix. In this realm, utilising biosurfactants or microorganisms capable of biosurfactant production and contaminant resistance is feasible (Chaprão et al., 2015; Geetha et al., 2018). The environmental applications of biosurfactants are founded on two primary interaction processes. Firstly, biosurfactants enhance substrate bioavailability. Secondly, they render the cell surface hydrophobic, promoting interaction with surfaces and facilitating the engagement of hydrophobic substrates with bacterial cells (Pacwa-Płociniczak et al., 2011). Subsequent sections unfold the key environmental applications of biosurfactants documented in the literature.

Biosurfactants in the pharmaceutical industry

In the fields of pharmaceuticals, biosurfactants offer a compelling alternative to synthetic surfactants due to their antibacterial properties. Their natural origin and effectiveness make them attractive for these industries, where safety and efficacy are paramount. Koji et al. (2002) and Mukherjee & Das (2010) demonstrated the diverse pharmaceutical applications of biosurfactants. These include but are not limited to gene delivery, respiratory arrest agents, immunological adjuvants, antiadhesive agents in surgical implants, inhibition of pathogenic organisms' adhesion to solid surfaces, recovery of intracellular products, antimicrobial, antiviral, and anticancer activity, as well as agents for promoting skin fibroblast metabolism. Markande et al. (2021) found that biosurfactants, specifically glycolipids and lipopeptides, can prevent the formation of fibrin clots and improve the electrical conductivity of biomolecular lipid membranes.

Additionally, these compounds are useful as antiadhesive and antibiofilm agents for medical devices and transplant procedures. This is due to their ability to reduce surface tension between immiscible and miscible liquids, disrupt hydrogen bonding, and enhance interactions between hydrophilic and hydrophobic molecules (Markande et al., 2021). Microbial surfactants are currently utilized as antioxidants in the food and pharmaceutical industries. Antioxidants are crucial compounds that neutralize free radicals generated during various physiological processes, thereby preventing oxidative stress, also known as oxidative damage caused by the highly reactive nature of free radicals (Valko et al., 2007). In a study by Abdollahi et al. (2020), the antioxidant capacities of two biosurfactants from autochthonous strains were compared. The findings revealed that the surfactin-type biosurfactant from Bacillus amyloliquefaciens NS6 exhibited a stronger antioxidant capacity than the rhamnolipid-type biosurfactant from Pseudomonas aeruginosa MN1. However, surfaces treated with rhamnolipid showed superior antiadhesive and antibiofilm properties compared to those treated with surfactin (Abdollahi et al., 2020). Heavy metal-tolerant Bacillus strain NK1 produced a biosurfactant that exhibited strong antibacterial activity and may be used as a therapeutic molecule for a variety of microbiological diseases (Sriram et al., 2011). Potential uses for antimicrobial biosurfactants in the food, pharmaceutical, and biomedical sectors come from microorganisms linked to human health, which further needs to be explored (Giani et al., 2021).

Industrial uses of biosurfactants in pesticides and food industry

Surfactants play an indispensable role as adjuvants for fungicides, insecticides, and herbicides in agriculture. Synthetic surfactants currently employed in the pesticide industry enhance the efficacy of pesticides, serving as emulsifying, dispersing, spreading, and wetting agents. Moreover, owing to their protective properties, these surfactants find application in modern agriculture as pesticides (Rostás & Blassmann, 2009). Anionic, cationic, amphoteric, and nonionic surfactants are widely utilized across various sectors of pesticide production (Mulqueen, 2003). Studies indicate that Burkholderia and Pseudomonas bacteria can degrade paddy fields' surfactants (Eriko et al., 2002). The widespread use of essential agricultural products like insecticides produced through biosurfactant synthesis is evident in agricultural settings. Consequently, agrochemical firms must develop efficient formulation technologies to meet this demand. In advanced food formulations, biosurfactants find application as thickeners, stabilizers, and emulsifiers (Campos et al., 2013; Eras-Muñoz et al., 2022). In the food industry, biosurfactants are commonly employed to enhance food texture and prolong shelf life. Additionally, they serve as emulsifiers, contributing to the stability of emulsions (Nitschke and Silva, 2018). Natural surfactants are particularly favoured for their remarkable stability under harsh conditions of salinity, temperature, and pH, rendering them highly relevant for industrial applications (Ghasemi et al., 2019). Rhamnolipids, for instance, are employed in the food industry to enhance the quality of baked goods and confections (Campos et al., 2013).

Prevention of pathogenic microorganism adhesion

Recent studies have revealed that biosurfactants can prevent harmful organisms from adhering to solid surfaces or infection sites (Das et al., 2009). Consequently, a novel and potentially successful strategy could involve preventing biosurfactants from adhering to solid surfaces beforehand, thereby thwarting the colonization of harmful bacteria (Rivardo et al., 2009). In experiments, the pre-coating of vinyl urethral catheters with a surfactin solution before inoculation with media led to a reduction in biofilms formed by Salmonella typhimurium, Salmonella enterica, Escherichia coli, and Proteus mirabilis (Rodrigues et al., 2004). Furthermore, Rodrigues et al. (2004) demonstrated that biosurfactants significantly reduced bacterial populations on voice prostheses once biofilm formed, consequently decreasing airflow resistance.

Other role of biosurfactants

Das et al. (2009) demonstrated that marine Bacillus circulans produce biosurfactants exhibiting potent antibacterial efficacy against a spectrum of microbial strains, encompassing gram-positive, gram-negative, pathogenic, and semi-pathogenic strains, including multidrug-resistant (MDR) strains. In a study by André et al. (2007), researchers evaluated 29 bacterial strains for resistance to biosurfactants derived from Bacillus subtilis R14. Their findings revealed that lipopeptides exerted broad-spectrum antibacterial effects, including efficacy against microbes displaying profiles of multiple antibiotic resistance (Kumari et al., 2023). Following fermentation, cells have been lysed using surfactants as a step in the process of recovering intracellular products. Escherichia coli, for instance, was selectively permeabilized using reverse micelle solutions to facilitate the extraction of penicillin acylase (Singh et al., 2007). Moreover, while biosurfactants are not widely used in the fashion industry, their unique properties make them promising candidates for sustainable innovation in textile processing, leather production, and packaging materials. As research and development in this area continue to advance, biosurfactants may play an increasingly important role in making fashion more environmentally friendly and socially responsible. Fig. 4 displays the application of biosurfactants in diverse fields.Fig. 4 Applications of microbial biosurfactants in diverse fields.

Fig 4

Microbial biosurfactants for pesticide remediation

Food production increased dramatically during the Green Revolution due to the widespread usage of pesticides (Raj et al., 2024c). However, if appropriate action is not taken to remove pesticides from the environment, the consequences are now felt by present generations and will be felt by future generations (Raj et al., 2021). Farmers utilised chemical fertilizers and pesticides (including herbicides, fungicides, insecticides, and rodenticides). According to research, only 1 % of pesticides sprayed kill the intended target species; the remaining 99 % interact with the soil to generate more complex compounds that harm the environment and human health (Rawat et al., 2020). Biosurfactant-produced micelles may enhance hydrophobic pesticide chemicals' solubility and bioavailability by reducing surface and interfacial tension when present at quantities above the critical micelle concentration (CMC). One notable metabolite for this purpose is biosurfactant (Sajadi Bami et al., 2022; Rasheed et al., 2020). Until the critical micelle concentration (CMC) is reached, the concentration of surface-active molecules drives the actions of biosurfactants. Effective biosurfactants have a low CMC and require fewer biosurfactants to reduce surface tension (Bhatt et al., 2021b; Pacwa-Płociniczak et al., 2011).

Desorption from soil particles reduces surface tension, accelerating the deterioration process (Twigg et al., 2019). The most common mechanisms that play a significant role in the bioremediation of pesticides by biosurfactants include precipitation-dissolution, ion exchange, electrostatic interactions, and counter-ion binding (Pardhi et al., 2022; Wu et al., 2019). Consequently, the soil becomes fertile, free of pollutants, and suitable for farming (Jimoh & Lin, 2019; Yesankar et al., 2023).

Pesticide metabolism by microbes

Pesticides target acetylcholinesterase receptors, which microbes lack, so they are unaffected by these chemicals (Raj et al., 2024c). Moreover, many bacteria that degrade xenobiotics are proficient at producing biofilms and biosurfactants. These substances aid in the adsorption and enhance the solubility of pesticides, making them more accessible for bacterial breakdown (Raj et al., 2023).

The microbial biotransformation of pesticide molecules involves several key processes: conjugation, degradation, and translocation. When pesticides enter bacterial cells, they undergo metabolic and molecular changes. Initially, the pesticide is absorbed through the bacterial cell membrane. It undergoes various metabolic transformations inside the cell, including hydrolysis, which breaks it down into non-toxic metabolites. These processes ensure the pesticide is wholly mineralized or converted into harmless byproducts, effectively neutralizing its harmful effects. Additionally, bacterial conjugation can enhance the spread of degradation capabilities among microbial communities, further aiding in detoxification (Bhatt et al., 2021a; Kupski et al., 2019). One of the most crucial functions of biosurfactants is their ability to separate harmful pesticide molecules from soil or water, making these pollutants more accessible for microbial degradation. By breaking the bond between pesticides and their environmental matrix, biosurfactants enhance the bioavailability of these contaminants. This increased availability allows microorganisms to expedite the remediation process more efficiently, leading to faster and more effective detoxification of polluted environments. Additionally, biosurfactants can help disperse pesticides, preventing their accumulation and reducing their overall toxicity in the ecosystem (Raj et al., 2021; Rasheed et al., 2020). Biosurfactants aid in pesticide bioremediation through various interactions, including precipitation-dissolution, ion exchange, counter-ion binding, and electrostatics. These mechanisms assist to separate and solubilize pesticide molecules, increasing their availability for microbial breakdown. Precipitation-dissolution includes converting pesticides from solid to dissolved forms, making them simpler to obtain. Ion exchange and counter-ion binding aid in releasing pesticide ions from their bound state, whilst electrostatic interactions help destabilise the bindings between pesticides and soil or water particles. These interactions generate an environment where microorganisms can more efficiently degrade and neutralise toxic pesticides, resulting in better bioremediation outcomes (Patowary et al., 2017; Twigg et al., 2019). In bioremediation, microorganisms are better at absorbing water-soluble pesticides. Biosurfactants are essential in separating hydrophobic pesticides from the aqueous phase by generating emulsions at critical micellar concentrations. This separation enhances pesticide bioavailability to microbial degraders, which improves bioremediation effectiveness. When pesticides are discharged into the environment, biosurfactants make the pollutants more accessible to microorganisms, lowering the danger of soil and water contamination. As a result, the soil improves in purity, fertility, and suitability for agricultural use. This procedure reduces environmental pollution and supports sustainable agriculture by improving soil health and production (Fenibo et al., 2019; Moya Ramírez et al., 2015).

Once bacteria are isolated in pure culture and presumptively identified, their ability to utilize the pesticide as a sole carbon or nitrogen source or through co-metabolism can be confirmed. Genetic studies on pesticide-degrading bacteria have focused on cloning and identifying the enzymes responsible for pesticide degradation. It is well-established that plasmid-encoded catabolic sequences play a significant role in breaking down pesticides (Sayler et al., 1990). The potential for the propagation of these plasmid-encoded catabolic genes has long been recognized, which might explain the ineffectiveness of certain rapidly degradable pesticides in specific soils (Pemberton and Nature, 1997). This gene propagation enables bacteria to adapt and degrade various pesticides, enhancing bioremediation. Understanding and harnessing these genetic mechanisms can lead to more effective strategies for managing pesticide pollution and improving soil health. Fig. 5 shows the interaction of biosurfactants with pesticides and soil particles.Fig. 5 Interaction of biosurfactant with pesticides and the microbes.

Fig 5

Improving the solubility and/or degradation of pesticides using biosurfactants

If appropriate steps are not taken to remove pesticides from the environment, current generations are already dealing with the consequences, and future generations will also face them (Raj et al., 2021). Due to their weak aqueous solubilities and bio-availabilities, pesticides are very difficult to degrade and/or remove from the environment. Pesticides typically have severe harmful effects because of their high concentrations. The World Health Organization (WHO) has classified quinalphos (an organophosphorus substance) as a moderately harmful chemical based on the acute hazard classification of insecticides. Quinalphos is poisonous, although it is still used in agriculture.

Methods for removing pesticides described in the literature include using multifunctional compounds, such as biosurfactants (BSs) and other chemicals, either in pure or crude form. Using microorganisms to break down and/or remove pesticides or other contaminants to lower their concentrations is beneficial. The use of chemical surfactants in pesticide formulations—the majority of which are derived from petroleum or petrochemicals—has harmful effects on the environment and on both plants and the species that live alongside them. The use of BSs with similar qualities is a profitable solution to avoid these risks (Ali et al., 2022). BSs can increase the bioavailability of hydrophobic insecticides in the environment for cleanup purposes by dissolving or dislodging them. BSs can combat hydrophobicity and limited pesticide accessibility due to their amphiphilic nature, making them more effective in interacting with pesticides. Metabolically adaptable BS-producing strains are typically effective at removing pesticides from agricultural soils (Jia et al., 2013).

The pesticide-contaminated artichoke crop that harbour the PGPR strain Pseudomonas rheophile S211 was grown on media based on olive mill wastewater (OMWW). The strain's molecular analysis indicated essential genes' presence and participation in producing 1-amino phytopathogens carboxylate deaminase, putative dioxygenases, auxin, pyoverdine, and exopolysaccharide levan, among other compounds. With a yield of 720.80 ± 55.90 mg/L, an emulsification index (EI) of 90 %, and an oil displacement of 63.58 cm2, the strain S211 also generated Rhamnolipid-biosurfactant (RL-BS). For high BS production, the ideal conditions were 15 % (v/v) OMWW, 40 °C temperature, 6.0 pH, 0.5 % (v/v) inoculum size, and up to 8 days of incubation. The BS demonstrated good stability over a wide range of temperatures (40–90 °C), pH (6–10), and large NaCl concentrations (up to 300 mM), indicating its potential for use in a variety of circumstances (Gaur et al., 2019b). Utilizing RL made from Lysinibacillus sphaericus IITR51, Gaur, Bajaj, et al. (2019) dissolved endosulfan, hexachlorocyclohexane, and other chemicals. With an EI of 48 %, the BS considerably decreased water static surface tension (SFT) from 72 to 52 N/m. The BS also showed good stability throughout a range of salt concentrations (2–14 %), pH (4.0–10), and temperatures (4–100 °C). At a concentration of 90 mg/L BS, the RL effectively dissolved hexachlorocyclohexane by up to 1.8-fold, 7.2-fold, and 2.9-fold, respectively. The bacterium was also resistant to heavy metals, including arsenic, lead, and cadmium and could use aromatic organic chemicals like benzoic acid, chlorobenzene, and 3- and 4-chlorobenzoic acid.

Due to their harmful effects, bioremediation of pesticide-polluted areas requires immediate attention. BSs have similar activity to SDS and higher efficiency at solubilizing pollutants or chemicals than Tween 80 (Wattanaphon et al., 2008). Glycolipid BSs from Burkholderia cenocepacia BSP3, an isolate from fuel oil-contaminated soil, were reported by Karamchandani et al. (2022). Fig. 6. displays the mechanism of action of biosurfactants in facilitating the remediation of pesticides.Fig. 6 Mechanism of action of biosurfactants in facilitating remediation of pesticides.

Fig 6

Role of microbial biosurfactants in organic waste and crop residue management

Agro-industrial wastages are organic and loaded with myriad nutrients like proteins, lignin, cellulose, starch, fibres, minerals, vitamins etc. Interruptible and solid waste is emerging as an acute problem for agriculture in the form of disposable material from various agro-industries. Asia generates around 4.4 billion tons of waste annually, and India contributes more than 350 million tons from various pathways throughout the country (Madurwar et al., 2013). These waste materials are discarded untreated, which causes great environmental issues. Recycling organic wastes for biosurfactant production provides a green and environmentally friendly biovalue cascade. Microbial biosurfactants are emerging as potential agents for the cleanup of organic waste and agricultural residue. These surface-active compounds, generated by a variety of microbes, have distinct features such as lowering surface and interfacial tension, emulsifying hydrophobic substances, and increasing microbial activity (Puyol McKenna et al., 2024). Despite their numerous advantages over traditional synthetic surfactants, biosurfactants face challenges due to their high production costs and low yields. Over the past few decades, extensive research has focused on facilitating their commercial production using low-cost substrates, particularly carbon sources, to replace more expensive chemical alternatives. Examples of agro-waste-containing carbohydrates that can be utilized for biosurfactant production include rice water and wastewater from cereal processing (Cerda et al., 2019). These low-cost agro-industrial waste products are effective substrates for biosurfactant synthesis, thereby significantly reducing production costs. Microbial biosurfactants, especially those derived from sunflower cake, function to reduce surface tension and produce biosurfactants from substrates such as leftover cooking oil, potato peelings, and sunflower cake. These waste streams can be used as renewable and reasonably priced feedstocks for producing biosurfactants (Biktasheva et al., 2024). The production of biosurfactants using organic waste as a substrate is gaining attention (Eras-Muñoz et al., 2022). Biosurfactants such as glycolipids and rhamnolipids have been effectively produced from a variety of agro-industrial wastes, including waste from soybean oil refineries and olive oil mill effluents. Fruit and vegetable processing byproducts, such as orange peels and cashew apples, have been explored as biosurfactant manufacturing substrates and have been shown to significantly lower surface tension. These wastes are suited for microbial fermentation due to their carbohydrate-rich content, which can produce a variety of biosurfactants with potential industrial uses (Domínguez Rivera et al., 2019). It has been shown that agro-industrial wastes like orange peel and date molasses are good substrates for the synthesis of biosurfactants, which improves waste management and profitability. Studies also show that certain fruit and vegetable by-products can serve as viable carbon sources for microbial biosurfactant production. The high organic content of industrial wastes, especially those from the dairy and oil processing sectors, makes them attractive substrates for the synthesis of biosurfactants. Microbial species like Candida are crucial to the efficient transformation of these wastes into valuable biosurfactants (Mohanty et al., 2021). Numerous studies have demonstrated that agricultural waste lignocellulosic biomass can be processed into a variety of products, including nutrients for biosurfactant synthesis (Gudiña et al., 2011; Das & Kumar, 2018). This lignocellulosic biomass provides a nutrient-rich environment for microbial growth (Panadare & Rathod, 2015). For example, Penicillium citrinum H9, a lignocellulolytic mold, has shown the capability to hydrolyze agricultural wastes such as hay and straw (Mardawati et al., 2018; Ni'matuzahroh et al., 2020). Specifically, rice straw hydrolyzed by Penicillium citrinum H9 yielded up to 209.25 g/mL of sugar (Mardawati et al., 2018). Additionally, studies have reported the synthesis of surfactin when examining various potato processing effluents. Bacillus subtilis 21332 was identified as the bacterium responsible for producing surfactin from potato effluents (Begum et al., 2023; Karnwal, 2021). Furthermore, Bacillus pumilus grown on potato peels was found to produce lipopeptide biosurfactants (Sharma et al., 2015). Another study demonstrated that Bacillus mojavensis A21 utilizes potato waste to produce lipopeptide biosurfactants, specifically isoforms of fengycin and surfactin (Ayed et al., 2019). Das and Kumar investigated the production of rhamnolipids by Pseudomonas azotoformans AJ15 using potato peels and sugarcane bagasse as substrates (Das & Kumar, 2018). By utilizing crop residues as substrates for biosurfactant production, farmers can manage agricultural waste effectively. This approach not only reduces the environmental impact of burning or discarding crop residues but also contributes to soil health by enhancing microbial activity and nutrient availability (Mohanty et al., 2021).

According to reports, adding biosurfactants to compost piles speeds up the decomposition of organic matter, cutting down on composting times and enhancing the quality of the finished product. Furthermore, biosurfactants lessen the generation of odorous chemicals during composting by promoting the full breakdown of organic waste. Agricultural areas can benefit from the use of biosurfactants, which promote the breakdown of crop leftovers and replenish soil nutrients. Moreover, it facilitates the microbial degradation of pesticide residues and other contaminants in crop waste, reducing environmental impact (Roy, 2017; Sánchez, 2022; Abraham et al., 2023). Anaerobic digestion and composting are two examples of bioconversion technologies that have been demonstrated to function more efficiently when microbial biosurfactants are used. As a result, waste biomass is converted into high-value organic fertilizers, advancing the circular economy in agriculture (Kiruba et al., 2022). Overall, microbial biosurfactants offer a multifaceted approach to managing organic waste and crop residues, enhancing biodegradation, improving soil health, and supporting sustainable agricultural practices. Their application can lead to more efficient waste management and better environmental outcomes (Eras-Muñoz et al., 2022).

System biology and synthetic biology approaches for tailoring biosurfactant properties

Systems biology techniques offer deep insights into the intricate relationships behind the synthesis of biosurfactants. These techniques include computational modelling, omics technologies (genomics, transcriptomics, proteomics, and metabolomics), and synthetic biology tools. Identifying metabolic pathways, uncovering metabolic bottlenecks, and predicting genetic targets for metabolic engineering are all made possible by integrating multi-omics data. Developing new biosurfactant synthesis routes, higher catalytic efficiency through enzyme engineering, and increased biosurfactant output through chassis optimization are all made possible by synthetic biology (Malla et al., 2022). Researchers have fully realised the potential of biosurfactants as adaptable and sustainable biomolecules for various industrial, environmental, and medicinal applications by utilising advancements in genetic manipulation and systems biology (Lamilla et al., 2021). By engineering microorganisms that produce biosurfactants and developing innovative biosynthetic pathways, scientists have manipulated the structures of biosurfactants to improve their properties and maximize their yield (Jimoh et al., 2021). Biosynthetic enzymes responsible for biosurfactant production have been engineered using directed evolution and rational protein design approaches. This has allowed for the development of variations with changed substrate specificity, catalytic activity, and product specificity. For instance, modification of the glycosyltransferases' substrate specificity during glycolipid biosynthesis has produced biosurfactants with customized sugar moieties, which can change the physicochemical characteristics and biological activities of the resulting compounds (Fujinami et al., 2021). Moreover, combinatorial biosynthesis techniques like enzyme fusion and domain shuffling have been applied to produce hybrid biosurfactants with synergistic qualities originating from many biosynthetic pathways. For example, a bidirectional synthetic approach makes it simple to synthesise aureosurfactin, which allows both enantiomers to have surface tension activity comparable to that of recognised biosurfactants (Mittendorf et al., 2023). As a result, synthetic biology has enormous potential to advance the science of biosurfactant engineering by providing flexible techniques and tools for modifying the characteristics of biosurfactants to fit a range of applications. Researchers can rapidly develop next-generation biosurfactants with improved performance, sustainability, and affordability by using synthetic biology, which will open the door for their broad use in various industrial sectors.

Conclusion and future prospects

This review emphasises how important microbial biosurfactants are as environmentally friendly substitutes for pesticide contamination and the advancement of environmental sustainability. It is clear from a thorough examination of their kinds, characteristics, manufacturing processes, and uses that microbial biosurfactants are viable options for environmentally friendly industrial and agricultural processes. Their capacity to increase the solubility of pesticides, stimulate biodegradation, and minimize environmental pollution represents a major advancement towards sustainable pest control techniques. Moreover, their industrial application in various industries, including the food sector, shows biosurfactants' adaptability and economic potential. This review opens the door to improving yield and streamlining manufacturing procedures by clarifying the genetic control of biosurfactants and the molecular mechanisms behind their formation. Furthermore, sophisticated analytical methods enable accurate identification and characterization, leading to a more profound comprehension of their structure-function correlations. Microbial biosurfactants play an important role in organic waste management since they provide an alternative substrate for production, hence contributing to a circular economy approach in environmental applications. Advancements in synthetic biology have opened the door for forming next-generation biosurfactant molecules for sustainable agriculture.

Looking ahead, several directions for more research and development in microbial biosurfactants become apparent. First, more investigation into new microbial strains and genetic engineering techniques might lead to more efficient production of biosurfactants with a wider range of uses. Furthermore, for broad acceptance in industrial settings, developing scalable and affordable production techniques will be essential for broad industrial implementation. Furthermore, investigating the synergistic relationships between microbial biosurfactants and other environmentally friendly farming methods, such as using organic fertilizers and biocontrol agents, may provide integrated pest management plans that are more sustainable and effective. Additionally, exploring the potential of biosurfactants in cutting-edge disciplines like bioremediation and nanotechnology offers new avenues for their use beyond their traditional uses. Moreover, for microbial biosurfactants to be widely accepted and used, it will be crucial to overcome regulatory issues and raise public knowledge of their advantages. To fully realize the promise of microbial biosurfactants for preserving the environment, research, development, and implementation activities will be driven by collaborations between academia, industry, and government agencies.

Funding

SSM would like to thank the UGC-University Non-NET fellowship. AR would like to acknowledge the funding from the Indian Council of Medical Research in the 10.13039/501100001411 form of ICMR-SRF (Grant No. 3/1/2 (10) Env/2021-NCD-II ) to carry out this work. AK gratefully acknowledges DST-SERB for financial support obtained through the project grant of (CRG/2021/003696 ), New Delhi Govt of India.

CRediT authorship contribution statement

Shiv Shankar Markam: Writing – original draft. Aman Raj: Writing – original draft, Writing – review & editing. Ashwani Kumar: Supervision, Conceptualization, Writing – review & editing. Mohammed Latif Khan: Supervision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

Data will be made available on request.

Acknowledgements

SSM & AR thank the Department of Botany, Dr. Harisingh Gour Vishwavidyalaya, Sagar, (M.P.), for providing necessary lab facilities.
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