Biosurfactants E-Book
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- Herausgeber: Bentham Science Publishers
- Kategorie: Lebensstil
- Sprache: Englisch
- Veröffentlichungsjahr: 2024
Biosurfactants, derived from microbes and plants, exhibit diverse properties that help in emulsifying and foaming processes. With applications in pharmaceuticals, cosmetics, and agriculture, they also show antimicrobial and environmental benefits, such as oil removal in polluted areas. Biosurfactants show promise for pollution control and improving agriculture.
This reference covers the basic science and major applications of Biosurfactants. The book brings together contributions from experts in microbiology, cancer biology, pharmaceutical science, nanotechnology, plant biotechnology and environmental sciences into a single volume.
The key features of the book are
- Explains the basics of Biosurfactants
- Discusses novel applications of Biosurfactants in the field of medicine, agriculture and environmental sustainability.
- Includes special chapters that review the role of Biosurfactants in environmental remediation and omics research
- Includes detailed references in each chapter
This book is an essential resource for learners and professional trainees who require knowledge about Biosurfactants. It also provides information for anyone who is working on environmental sustainability projects.
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PREFACE
Biosurfactants are surface-acting molecules isolated from microbes (bacteria and fungi) and plants. The amphipathic nature of biosurfactants makes their application broader. Different types of biosurfactants are isolated and characterized i.e. glycolipids, lipopeptides, phospholipids and polymerics. These molecules have emulsifying, wetting, and foaming properties. So biosurfactants are used in pharmaceuticals, cosmetics, food, mining, and petrochemical industries. Research confirms their antimicrobial, anticancer and anti-biofilm formation capacities. They can remove oil from the contaminated soil of oil mines. Biosurfactants can be used in oil spillage aquatic areas to remove oil. They can scavenge heavy metals in contaminated soil and make the environment free from xenobiotics. With the help of nanotechnology, biosurfactants can be used to detect heavy metals in the environment. Nowadays, biosurfactants are used as potential agents in agricultural post-harvest technology. They play an important role in agrochemical industries.
In view of the above discussion, the overarching aim of this book is to discuss major applications of biosurfactants in the fields of healthcare, agriculture and the environment.
The unique features of this book are as follows:
• The book is a contribution of experts from microbiology, cancer biology, pharmaceutical science, nanotechnology, plant biotechnology and environmental sciences.
• The book discusses some novel applications of biosurfactants in the fields of medicine, agriculture and the environment.
The book, in total, comprises 11 chapters written by experts working in the respective aspects of biosurfactants. For instance, Chapter 1 and 2 describe the screening of biosurfactant-producing organisms, the production of biosurfactants and their various applications. Chapter 3 and 4 interpret the application of biosurfactants in the healthcare sector, like various cancer treatments and neurological disorders.
Agricultural applications and food processing with the help of biosurfactants are well explained in chapters 5 and 6. Biosurfactants show vast applications in the environmental cleaning sector. Bioremediation, removal of heavy metal from soil and water by biosurfactants, and removal of oil from contaminated soil by biosurfactants are described in chapters 8, 9, 10 and 11.
We are very much thankful to all the contributing authors for their timely cooperation and support, without which this book would not have taken its final shape. We are also thankful to the series editors for their critical reviews and positive remarks to bring positive developments in the book.
List of Contributors
Biosurfactants: An Amazing Bioactive Compound
Sameer Ranjan Sahoo1,Manisha Mahapatra1,Arun Kumar Pradhan1,*Abstract
Biosurfactants are organic compounds synthesized by microorganisms such as bacteria, yeasts, or fungi. These compounds exhibit intricate chemical compositions and unique physical properties, often surpassing or rivaling synthetic surfactants. Furthermore, they typically have low toxicity towards freshwater, marine, and terrestrial ecosystems, making them environmentally favorable for various applications. To date, the primary focus of biosurfactant research has centered on enhancing the biodegradation and recovery of oil. These substances have demonstrated their utility in aiding the removal of hazardous contaminants from polluted areas due to their capacity to solubilize and emulsify harmful pesticides. Their versatility as chemical agents renders them suitable for deployment in both biotechnological and industrial applications. This review aims to provide readers with an extensive comprehension of recent advancements in utilizing biosurfactants and the microorganisms responsible for their production. This knowledge encompasses their medical applications, metal remediation technology, and hydrocarbon-related industries.
INTRODUCTION
Surfactants are a class of chemicals found in a wide range of fields, such as chemicals, fast-moving consumer goods, pharmaceuticals, and oil/water treatment. Biosurfactants are a family of chemical compounds synthesized by microorganisms, including hydrophilic and hydrophobic moieties. They tend to disperse interfaces between liquid phases (oil/water) of varying degrees of polarity by lowering interfacial and surface tension. Surfactants derived from microorganisms have numerous advantages over synthetic ones, including low toxicity, high biodegradability, multifunctionality, and mild manufacturing conditions.
An emulsifier is a substance composed of polymers of polysaccharides, lipopolysaccharides, proteins, lipoproteins, and glycolipids with a low molecular weight, known as a biosurfactant [1-3]. The former's molecular components are typically more effective in maintaining oil-in-water emulsions, although they reduce surface tension less than the latter's. It comprises non-interfering amphiphilic and multi-affinity polymers [4].
These compounds, primarily biosynthetically derived as secondary metabolites, play crucial roles in the proliferation and localization of microorganisms. The hydrophobic segment of these molecules comprises long-chain fatty acids, hydroxy fatty acids, or alkyl hydroxy fatty acids. On the other hand, hydrophilic components may include carbohydrates, amino acids, cyclic peptides, phosphates, carboxylic acids, and alcohols. The commercial surfactant market is from petrochemicals, plants, animal fats, and microorganisms. Research indicates that a substantial majority of commercially available surfactant products are petrochemical-based. One of the environmental agencies' transformative challenges involves developing innovative technologies to replace fossil fuel-based products with sustainable, biodegradable, green energy sources.
Numerous microorganisms demonstrate the capacity to utilize diverse substrates, including sugars, oils, alkanes, and various waste materials, for the biosynthesis of biodegradable surfactants [5]. Biosurfactants typically exhibit critical micelle concentrations (CMC) within the 1-200 mg/l range, accompanied by molecular weights ranging from 500 to 1500 Da [6]. Notably, they can rival or surpass the effectiveness of synthetic surfactants due to their distinctive advantages, such as high specificity, biocompatibility, and inherent biodegradability [7]. Biosurfactants represent a category of biodegradable surfactants primarily produced by bacteria and yeast [8-10].
Lipopeptides are mainly produced by Bacillus spp. followed by Brevibacterium aureum and Nocardiopsis alba. Glycolipids by Pseudomonas, Burkholderia, Mycobacterium, Rhodococcus, Arthrobacter, Nocardia, Gordonia. Some yeasts and fungi such as Starmerella, Yarrowia and Pseudozyma, Ustilago scitaminea also found to produce glycolipids. Thiobacillus sp. are found associated with phospholipids production [11].
The adaptability and utility of the molecules have generated attention in industrial and ecological applications such as bioremediation, soil cleansing, better oil recovery, and processing [12]. Emerging commercial applications have been found in chemical, textiles, agricultural, pharmaceuticals, food, and manufacturing industries [10, 13].
Biosurfactants accumulate at the intersection of two immiscible phases or the contact of a liquid and a solid. Lowering surface and interfacial tension minimizes repulsive forces between two distinct phases, allowing for easier mixing and contact. Below are some examples of biosurfactants and their application refer to Table 1.
A biosurfactant's ability to alter surface tension, maintain emulsions, and probe hydrophilic-lipophilic properties determines its potency and balance (HLB). The HLB number shows if the biosurfactant is a water-in-oil emulsion or an oil-in- water emulsion. This criterion may be used to assess the suitability of biosurfactants. Emulsifiers with low HLBs help stabilize water-in-oil emulsions, while emulsifiers with high HLBs promote water solubility [14, 15]. The hydrophobicity of the bacterial cell surface is also influenced by biosurfactants (CSH). This capacity was described by Al Tahan et al. [16]—modifications in the bacterial cell's structure surface make carbohydrates more accessible to the microbial cell.
Biosurfactants: Real Prospects for Industrial Use
Increasing environmental concerns, biotechnology advancements, and increa- singly severe laws have made biosurfactants a viable alternative to synthetic surfactants on the market [27]. The number of biosurfactant papers and patents has expanded dramatically in recent years [28]. Worldwide, patents on biosurfactants, emulsifiers, and other features have been issued. Petroleum-related sectors acquired the most patents (33%), followed by cosmetics (15%), pharmaceuticals (12%), and bioremediation (11%), with the bulk of patents covering sophorolipids, surfactins, and rhamnolipids.
Biosurfactants are increasingly being used in industry. Many difficulties, however, must be solved before broader adoption may be contemplated. These concerns are connected to yield and manufacturing costs, as well as the time and effort necessary to adapt the molecule of choice for a specific application [29, 30]. Transparency Market Research recently conducted a comprehensive assessment of the biosurfactants industry and market trends™.
Environmental Applications
The unintended or purposeful release of organic and inorganic substances into the environment is a common cause of pollution from industrial activity. These chemicals quickly bond to soil particles, making clean-up difficult. Is it possible to replicate the removal of pollutants by using biosurfactants to clean organic molecules such as hydrocarbons? The washing and solubilization procedure fluidizes and eliminates emulsification. The use of biosurfactants in the remediation of inorganic substances such as heavy metals, on the other hand, promotes chelation promotes the removal of such ions during cleaning phases, which is assisted by chemical interactions between amphiphiles and metal ions.
It is becoming increasingly common for industry to use biosurfactants. In order to increase the adoption rate, several issues must be addressed. These issues involve yields and production costs, including downstream processing and tailoring molecules for specific applications [29, 30]. A market research firm, Transparency Market Research, analyzed the biosurfactant industry and trends recently.
Biosurfactants and Bioremediation
Bioremediation is now famous as a potential low-cost, high-performance solution for tackling environmental contamination problems. Ranging from polyaromatic hydrocarbons, jet fuel, gasoline, diesel fuel, and the benzene, toluene, ethyl benzene, and xylene cluster, acid mine drainage pesticides, munitions compounds (e.g., trinitrotoluene), and inorganic heavy metals to crude oil, biotechnology products objects are being created in commercial and government laboratories all over the world to find and develop biotechnological solutions that will help in the economically and effectively resolution of pollution concerns in an ecologically acceptable way [31, 32]. Amphiphiles can alter interface physicochemical conditions, influencing chemical distribution among phases. Biosurfactants introduced to this system can interact with abiotic particles and bacterial cells.
This changes the processes of organic contaminants' micellarization and emulsification, interaction with absorbed pollutants, and sorption to soil particles, resulting in changes in cell-envelope composition and hydrophobicity. Among the most critical changes in bacterial composition are interactions between micelles and cells [33]. These processes can be employed to boost the bioavailability of sparingly soluble pollutants and, hence, the biodegradation rate. It can also be used to prevent biodegradation.
Surfactants are developing as a technique for improving the accessibility and bioavailability of hydrophobic compounds, hence supplementing conventional (bio)remediation strategies. Unfortunately, most of the research on biosurfactants have been done in the laboratory, and large-scale plotting is uncommon. Additionally, most field service technicians must become more familiar with surfactant technology, especially biosurfactants. To date, the literature on the effects and efficacy of the molecules needs to be more extensive and conclusive.
Biosurfactants are mainly used in the biodegradation of crude oil [34] and improved oil recovery systems [35, 36]. Strikingly, a large-scale bioremediation study conducted after the 1989 Alaska oil spill showed that nutrient-stimulated biomass effectively increased the availability and biodegradability of oil-affected shorelines. A potential role for biosurfactants produced by microbial flora has been thwarted [37]. According to Chakrabarty [38], biosurfactants produced by Pseudomonas aeruginosa can effectively disperse oil into tiny droplets, improving the bioremediation of oil-contaminated shorelines.
Biosurfactants' Role in Biological Degradation Processes
Using biosurfactants to improve bioremediation efficiency in hydrocarbon-contaminated settings is a potential method. They have the potential to increase hydrocarbon bioremediation in two ways. The first is to increase the bioavailability of the microbial substrate, and these conditions interact with the cell surface, which makes the surface more hydrophobic, making it easier for the hydrophobic substrate to adhere to bacterial cells [39]. Biosurfactants increase the surface area of insoluble molecules and lower surface and interfacial tension, enhancing hydrocarbon mobility and bioavailability. As a result, biosurfactants promote biodegradation and hydrocarbon elimination. Biosurfactants, which mobilize, solubilize, or emulsify hydrocarbons, are predicted to promote hydrocarbon biodegradation.
The mobilization process takes place at concentrations lower than the biosurfactant CMC. Biosurfactants diminish surface and interfacial tension between air/water and soil/water systems at such concentrations. Contact between a biosurfactant and a soil/oil system increases the contact angle. It decreases the capillary forces that hold the oil and soil together as the interfacial forces decrease. The solubilization process takes place sequentially over the biosurfactant CMC. The biosurfactant molecules form micelles at these concentrations, considerably improving oil solubility. Outside the aqueous phase, the hydrophilic ends of the biosurfactant molecules are exposed, while the hydrophobic ends are bound together within the micelles. This creates a favorable environment for hydrophobic organic compounds within the micelles.
Emulsification produces an emulsion, which is made up of microscopic droplets of fat or oil floating in a liquid (usually water). Emulsifiers are also high molecular weight biosurfactants refer to Fig. (1). They are frequently utilized as adjuvants in bioremediation and removing oil molecules from ecosystems.
Fig. (1)) Methods of hydrocarbon elimination by biosurfactants based on molecular mass and concentration.Bacteria with low cell hydrophobicity can attach to micelles or emulsified oils, whereas bacteria with strong cell hydrophobicity can directly contact oil droplets and solid hydrocarbons [40]. Microorganisms and hydrocarbons interact in three ways: access to water-solubilized hydrocarbons, direct contact of cells with big oil droplets, and interaction with quasi-solubilized or emulsified oils. Biosurfactants are presumed to be abletoalter carbohydrate up take patterns during different stages of microbial growth. Growth of On hydrocarbons, Gordonia sp. BS 29 developed extracellular bio emulsifiers and cell-associated glycolipid biosurfactants that changed surface hydrophobicity during hexadecane formation [40, 41].
Recent studies have revealed the then-alkane uptake process of Pseudomonas aeruginosa and the importance of rhamnolipids in internalizing hydrocarbons for later degradation. Hexadecane was made more readily available to bacterial cells due to the formation of microdroplets produced by the action of the biosurfactant. Recordings of biosurfactant-coated hydrocarbon droplets were performed following experiments using electron-microscopy. Remarkably, the biosurfactant-coated hydrocarbon droplet absorption mechanism was similar to active pinocytosis.
Numerous researchers [42-44] have observed that biosurfactants and the bacterial strains responsible for their production can expedite the availability and biodegradation of organic pollutants. For instance, Obayori et al. [45] investigated the biodegradability of biosurfactants derived from the genus Pseudomonas. Their study focused on the LP1 strain's exposure to crude oil and diesel. Reddy et al. [46] reported that the bacteria Brevibacterium sp., particularly the PDM-3 strain, achieved a remarkable degradation rate of 93.92% for phenanthrene, anthracene, and fluorene. In another study, Kang et al. [47] characterized sophorolipid and its effectiveness in the biodegradation of aliphatic and aromatic hydrocarbons. Their work emphasized enhancing the bioavailability of microbial consortia for biodegradation, thereby facilitating the bioremediation of hydrocarbon-contaminated sites characterized by low water solubility.
Employing biosurfactant-producing bacteria to bioremediate hydrocarbon-contaminated locations without specifying the surface-active chemicals' nature is an effective microbiological method. Cell-free culture medium containing biosurfactants can either be administered directly to the polluted region or diluted well beforehand. Biosurfactants are highly stable and effective in the media utilized for their synthesis. This is another advantage of this strategy.
Das and Mukherjee [48] discovered the importance of biosurfactant-producing strains in the bioremediation of crude petroleum hydrocarbon-contaminated environments. It was demonstrated that three biosurfactant-producing strains, Bacillus subtilis DM-04, Pseudomonas aeruginosa M, and Pseudomonas aeruginosa NM, could remediate petroleum-contaminated soil samples by treating soil samples with aqueous solutions of the biosurfactant obtained from each bacterial strain. Joseph and Joseph [49] were able to extract oil from petroleum sludge, which promotes bacterial development of biosurfactants. When refining crude oil, refineries generate a large amount of petroleum sludge. Storage tanks are typically used to store crude oil—oily contaminants remain on the bottom of the tank. Sludge is collected during tank cleaning and treated as waste. The use of biosurfactants often enhances the bioavailability and biodegradability of hydrophobes, but little is known about how emulsifier formation affects the biodegradation of complex hydrocarbon mixtures.
Bilge waste is a hazardous waste made up of saltwater and hydrocarbons. Residues, the main components of which are a complex mixture of n-alkanes, total soluble hydrocarbons, and insoluble solvents. Non-solvent complex mixtures predominantly comprise branched, cycloaliphatic, and aromatic hydrocarbons that exhibit the highest resistance to biodegradation. A consortium of bacteria that produce emulsifiers investigated the biodegradation of oily bilge waste. They discovered that the degree of biodegradation was 85% for n-alkanes, 75% for total dissolved hydrocarbons, and 58% for undissolved complex combinations.
Barkey et al. [50] investigated the solubilization of polyaromatic hydrocarbons (PAH), phenanthrene (PHE), and fluoranthene by alasane generated by Acinetobacter radioresistens KA53 (FLA). They also looked at the impact of arasan on the mineralization of PHE and FLA by Sphingomonas paucimobilis EPA505. They found that increasing bio-emulsifier concentration(from 50 to 500 gml1) linearly increased the water solubility of phenanthrene and fluoranthene and increased the mineralization of PAHs. Including arasan at concentrations up to 300 g mL1 quadrupled the rate of fluoranthene degradation and greatly enhanced the rate of phenanthrene degradation. The solubilization curves revealed that the apparent solubility of these compounds increased linearly with the addition of alacane in this concentration range, but increasing the alacane concentration beyond 300 gmL1 did not result in PAHM ineralization was not stimulated further. It has also been discovered that Enterobacter cloacae strain TU secretes an emulsifier exopolysaccharide (EPS) [51]. EPS has a robust emulsifying activity (E24=75). EPS can make the bacterial cell surface more hydrophobic while also neutralizing the cell's surface charge.
Microbial Improved Oil Recovery (MOER)
Initial oil recovery from wells frequently relies on conventional primary and secondary technologies, with certain wells recovering only 20% to 30% of their total oil reserves. Once these conventional methods reach their limits, as much as two-thirds of the oil in the reservoir may remain untapped. In such instances, tertiary oil recovery techniques, collectively known as Enhanced Oil Recovery (EOR), extract 10% to 15% of the remaining oil. These techniques encompass both chemical and microbiological approaches [52].
The microbiological approach, specifically Microbial Enhanced Oil Recovery (MEOR), leverages microbial processes involving the partial degradation of large oil molecules, gas production, selective plugging, and biosurfactant synthesis. In the case of biosurfactant production, it leads to reduced oil/water interfacial tension and the generation of oil-in-water emulsions, thereby enhancing oil mobility through rock fracture. Biosurfactants can be generated off-site in digesters and subsequently injected into oil reservoirs. Alternatively, introducing allophytic microbes or stimulating local bacteria through nutrient injection can produce them in situ [12].
A significant challenge in developing in situ production techniques involves the isolation of microbial strains capable of thriving in harsh conditions characterized by high pressure, salinity, elevated temperatures reaching up to 85 °C, and extreme pH values. Furthermore, some operators have reported issues related to clogging and corrosion when introducing microorganisms into wells.
The earliest possibilities for such applications were rhamnolipids, although all prominent families of microbial surfactants have been proposed for his MEOR uses. Lipopeptides such as surfactin, lichenin, and emulsan have been proven to increase oil recovery. Temperatures, pH levels, and salinities identical to those seen in petroleum reserves are detected in B. subtilis, P. aeruginosa, and Bacillus cereus. Oil displacement studies in glass micromodels were also carried out with the most promising suggested B. subtilis biosurfactant [51].
Most of the MEOR laboratory studies with biosurfactants were carried out in core flood systems, which simulated the features of oil reservoirs [52]. The core flood test used lipopeptide biosurfactants generated by the Bacillus mojavensis strain to assess oil recovery from carbonate reserves. It has been observed that treatment can recover up to 60% of the original oil in such cores [53].
She et al. [54] found that introducing various Bacillus cultures increased oil output from 4.89% to 6.96%. Xia et al. [55] achieved a 9.02% efficiency while injecting Pseudomonas aeruginosa cells. Numerous efforts have been attempted to identify unconventional biosurfactant-producing bacteria from sources capable of creating particularly efficient compounds in oil mobilization. Castrena-Cortez et al. [56] identified a stable consortium with the leading species Thermoanaerobacter. When evaluated in a low-volume oil recovery experiment, a granular porous medium revealed a 12% increase in oil release. In the same laboratory setting, the injection of surfactant-producing microorganisms and the application of biosurfactants were compared (one example is shown in Fig. (2).
Fig. (2)) Biosurfactants' increased oil recovery mechanism.The oil recovery performance of biosurfactants generated by Bacillus subtilis PT2 and Pseudomonas aeruginosa SP4 was compared to three synthetic surfactants: Tween 80, sodium dodecyl benzene sulfonate (SDBS), and alkyl polypropylene oxide [57,58]. Sodium sulphate (Alfoterra) in a study by Pornsunthorntawee et al. [ 59 ]. We employed a sand-filled column seeded with a motor oil compound for this. A surfactant solution was placed into the packed column to test if it improved oil recovery.
The biosurfactants generated by Bacillus subtilis PT2 and Pseudomonas aeruginosa SP4 demonstrated remarkable oil recovery efficiency, removing around 62% and 57% of the tested oil, respectively. Pseudomonas aeruginosa SP4 biosurfactant recovered oil more successfully than Bacillus subtilis PT2 biosurfactant. The synthetic surfactants tested had an oil recovery rate of 53-55%. Biosurfactants can also be utilised to recover hydrocarbon molecules from oil shale as a petroleum energy alternative fuel. Rhodococcus erythropolis and Rhodococcus ruber biosurfactants were effectively employed by Hadadin and colleagues for hydrocarbon desorption from El Lajjun oil shale [60].
Soil Cleaning Technology
The physio-chemical features of biosurfactants are distinctive of soil cleaning procedures, not their impact on bacterial metabolic activity or surface qualities [61]. However, these approaches can enhance the bioavailability of bioremediation. Aqueous biosurfactant solutions can also be used to leach low-solubility chemicals from soil and other media.
According to Urum et al. [62], synthetic surfactants such as sodium dodecyl sulphate (SDS) and rhamnolipid biosurfactants remove more crude oil than natural surfactants such as saponins (27%) [63]. Kang et al. investigated the application of soil detergents such as Sophorolipid, Tween (80/60/20), and Span (20/80/85) to liberate 2-methylnaphthalene from experimentally polluted soil. In removing stains, sophorolipid beats all other nonionic surfactants except Tween 80. This might be owing to its high hydrophilic-lipophilic balance (HLB). Surfactants with higher HLB appear to have increased 2-methylnaphthalene solubility. Lai et al. [64] used rhamnolipid, surfactin, tween80 and tritonX-100 to investigate natural and synthetic biosurfactant's ability to remove total petroleum hydrocarbons (TPH) from the soil.
TPH effectiveness was examined by washing (bio)surfactant solutions through low (LTC) and high (HTC) TPH contaminated soils. It was observed that 0.2 mass percent additions of rhamnolipids, surfactin, Triton X 100, and Tween 80 to LTC and HTC soils resulted in removal efficiencies of 23%, 14%,6%, 4%, and 63%, 62%, 40%, and 35% respectively. This indicates that of the four (biological) surfactants tested, rhamnolipids and sulactin were the most effective in their TPH removal and can be used as biostimulators for bioremediation against contaminated oil and gas surfaces.
METAL REMOVAL
The presence of heavy metals in the soil environment is highly hazardous to people and other species in the ecosystem. Heavy metals are so toxic that even low concentrations of heavy metals in soil can have serious consequences. Today, there are many ways to remediate soil contaminated with heavy metals. Non-biological remediation methods include excavation and disposal of contaminated soil at landfills and biological methods [65]. Biological processes remove metals from soil using plants (phytoremediation) or microorganisms (bioremediation). Metal pollution has traditionally been reduced using microorganisms. Heavy metals are not biodegradable; they can only change chemical states, which results in altered mobility and toxicity. Microbes may influence metals in several ways. Certain metals can be altered by redox or alkylation reactions. Microorganisms can collect metals through metabolism-independent (passive) or metabolism-dependent (active) absorption. Microorganisms can indirectly impact metal mobility by changing pH or generating or releasing chemicals that modify metal mobility [66, 67].
Studies have been undertaken to investigate the possibility of metal removal using biosurfactant anionic characteristics. Jwarkar and colleagues used the biosurfactant Pseudomonas aeruginosa BS2 to remove cadmium and lead [68]. Rhamnolipid scavenging of Cd and Pb was investigated using column experiments. Cadmium removal is more costly than lead removal. Within 36 hours, rhamnolipid (0.1%) removed over 92% Cd and 88% Pb. Rhamnolipids reduced toxicity and generated microbial activity (Azotobacter and Rhizobium) without affecting soil quality. Their profitability should also be evaluated. Assi et al. [69] compared the cadmium uptake capacity of two soil components, sepiolite and feldspar. Sepiolite has been determined to accumulate cadmium better than feldspar. Feldspar desorption (96%) was significantly higher than sepiolite desorption (10%).
Sorption can impair biosurfactants' capacity to remove pollutants from diverse soil components [70]. As a result, a rhamnolipids sorption assay was performed. The efficacy of rhamnolipid removal was reduced by sorption. Metal concentration was required for the absorption of the mono-rhamnolipid (R1). Sorption in organic decomposition followed the order hematite- kaolinite-MnO2 iris Camontmorillonite- gibbsite- humic acid-coated silica at low R1 concentrations. It was found that R1 is more adsorptive than R2 but removes metals more effectively than R2. This information helps in predicting the feasibility of rhamnolipid therapy and the needed dose of rhamnolipid formation. Utilizing rhamnolipids as the R2/R2 combination enhances the concentration of R1 in the repair solution. Kim and Vipulanandan [71] investigated the lead removal from water and soil (kaolinite). A linear isotherm represented desorption of lead from kaolinite. Vegetable oil was used for the production of biosurfactants. Using 10x CMC can remove approximately 75% of the lead in 100 mg/contaminated water. For best lead removal, the ratio of biosurfactant to lead was 100:1. FTIR spectroscopy demonstrated that the biosurfactant's carboxyl group was involved in the removal process. Micelle splitting may be described using the Langmuir and Freundlich models. Biosurfactant micelles distributed better than synthetic surfactants such as sodium dodecyl sulphate and Triton X-100.
The performance of Rhamnolipid was investigated by Dahrazma and Mulligan [72] in a continuous flow configuration (CFC) for heavy metal removal (copper, zinc, and nickel) from sediment samples of the Canadian Lachine Canal. Flow was simulated inside a column through the remediation technique. A continuous flow of rhamnolipid solution was pushed through a sediment sample. The rhamnolipid and additive contents, as well as the time and flow rate, were investigated. When applied, Rhamnolipid removed up to 37% of Cu, 13% of Zn, and 27% of Ni from sediments. When 1% NaOH was added to 0.5% rhamnolipid, copper removal increased up to fourfold compared to 0.5% rhamnolipid alone.
Metal Removal by Biosurfactants - Process Mechanism
Biosurfactants have clear benefits because of strains of bacteria that can produce surface-active chemicals that do not need to be able to live in soil contaminated with heavy metals. On the other hand, using just biosurfactants, regular fresh portions of these compounds are continuously added. The capacity of biosurfactants to form compounds with metals is helpful for bioremediation of heavy metal-contaminated soils. Ionic bonding allows anionic biosurfactants to create non-ionic compounds with more vital metals than metal-soil bonds.
Metal-biosurfactant complexes get de-absorbed with the decrease in interfacial tension. Cationic biosurfactants compete with surfaces charged negatively to displace same-charged metal ions. Biosurfactant micelles remove metal ions from the soil surface by binding metals with the polar head groups of micelles, causing metal mobilization in water refer to Fig. (3).
Fig. (3)) Biosurfactants’ activity mechanisms in metal-contaminated soil.Biosurfactants are used to trap trivalent chromium within micelles, enabling bacteria to tolerate and resist high concentrations of Cr (III). Nyanamani and colleagues [73] investigated biosurfactants of a marine strain, Bacillus sp. MTCC 5514 for chromium (VI) bioremediation. Sanitation of this strain was achieved by two processes: extracellular chromium reductase conversion of Cr(VI) to Cr(III) and biosurfactant removal of Cr(III). The first process transforms chromium from a hazardous to a less toxic state, whereas the second shields bacterial cells against chromium exposure (III). Both methods preserve bacterial cell function while conferring tolerance and resistance to high hexavalent and trivalent chromium levels.
Biosurfactants in Phyto-remediation
Plants inoculated with bacteria tolerant to heavy metals and producing biosurfactants can boost the efficacy of soil phytoremediation. Bacillus species strain J119 was tested for its potential to improve plant growth and cadmium uptake in soils loaded with varying amounts of Cd [74]. The tested strain colonized the rhizospheres of all studied plants, although the treatment only enhanced biomass and Cd absorption in tomato plant tissues. This shows that plant type influences the root colonization activity of the imported strains. Further research into the interaction of plants with the biosurfactant-producing bacterial strain J119, on the other hand, might lead to the development of new microbial-assisted phytoremediation approaches for metal-contaminated soils. Further study is needed on the use of biosurfactants and biosurfactant-producing bacteria in phytoremediation, particularly in areas polluted with organic and metallic pollutants.
Biosurfactants in Agriculture
The different roles of biosurfactants make them attractive candidates for future crop protection applications due to their different properties and involvement in biological regulation, antifungal drugs, and inducing systemic tolerance. Biosurfactants generally allow biological control by creating channels in the cell wall and disrupting the pathogen's cell surface [75]. Plants are primarily protected against phytopathogenic fungi by glycolipids such as cellobiose lipids, rhamnolipids, and cyclic lipopeptides, like surfactin, iturin, fengycin, and a variety of other biosurfactants [10].
Teichmann et al. [76] demonstrated that co-inoculation with wild-type Ustilago mydis sporidien prevented Botrytis cinerea infection of tomato leaves. Ustilagic acid, the first cellobiose lipid identified, is produced by this plant pathogen. Cellobiose lipids are natural surfactants with membrane-damaging characteristics that can induce cell death in yeast and mycelium at low doses [77].
Stanghellini and Miller [78] described how rhamnolipids function in various oomycete plant diseases by rupturing zoospore membranes and inducing zoospore lysis. Meanwhile, various research works on the relevance of rhamnolipids have been published in combating various phytopathogenic fungi. Devode et al. [79] discovered that the Pseudomonas species helps inhibit the viability of Verticillium microsclerotia. Piljac et al. [80] expected the collapse of Pythium hyphae incubation in a liquid medium containing both phenazine and P. aeruginosa PNA1-produced rhamnolipids. Both metabolites were shown to be crucial in the inhibition of Pythium species. The causative soil-borne diseases act synergistically.
A biosurfactant produced from rhamnolipids was discovered to have a direct antimicrobial effect, which suppressed Bacillus subtilis spore germination and mycelial growth. In addition, Ca2+ influx, the activation of mitogen-activated protein kinases, and the generation of reactive oxygen species were identified as early events in the grapevine response to the disease. The induction of plant defenses, accompanied by the production of various defense genes and hypersensitivity responses, has explained some of the mechanisms behind plant tolerance. Furthermore, rhamnolipid enhanced the defensive responses elicited by chitosan triggers and her B culture filtrate. Cinerea shows that a combination of rhamnolipids and additional effectors helps grapes resist botrytis [81].
Cyclic lipopeptides, like rhamnolipids, are another type of biosurfactant with antifungal activity against plant pathogens. Non-ribosomal peptide synthetases are guided by cyclic lipopeptide production, which is encoded by a vast gene cluster and consists of one module for each amino acid required for the oligopeptide. Each module is composed of several conserved domains, which involve the recognition, activation, transport, and binding of amino acids to peptide chains. The thioesterase domain governs peptide cyclization and release in the final module. This novel biosynthetic approach enables the incorporation of rare amino acids [82].
The structure, genes, biosynthesis, and control of known cyclic lipopeptides generated by numerous bacterial taxa have been disclosed by genome sequencing. Bacillus amyloliquefaciens GA1 genome has been sequenced, and four gene clusters promoting the synthesis of the cyclic lipopeptides surfactin, iturin A, and fengycin have been found (Arguelles-Arias et al. 2009). Current research has shown the presence of biosynthetic gene clusters that create secondary metabolites, including lipopeptides (surfactin, iturin, fengycin), which are involved in Bacillus' bioregulatory functions [83, 84].
Pseudomonas species are another major category of plant-associated bacteria with biological control capabilities via cyclic lipopeptide synthesis. Numerous research works focus on glycolipid-type biosurfactants and fungus interaction, and the zoospore-killing capacity of cyclic lipopeptides has also been found [82, 85], indicating their potential application as biocontrol agents.
Nanotechnology
and biosurfactants are advancing. Using a water-in-oil microemulsion, we created NiO nanorods [86]. A biosurfactant was added to heptane. The nickel chloride solution was then mixed into the biosurfactant/heptane mixture to create two different microemulsions, and adding ammonium hydroxide to the same hydrocarbon mixture created other microemulsions. To remove biosurfactants and heptanes, the microemulsions were pooled, and centrifuged, and the precipitate was washed with ethanol. The nanorods were 22 nm in diameter and 150-250 nm in length (pH 9.6). The form of the particles was affected by pH. This might be related to pH's influence on biosurfactants' morphology. Biosurfactants are a more ecologically friendly option.
In a study by Reddy et al., surfactin was shown to stabilize the formation of silver nanoparticles [87]. Sodium borohydrate was combined with silver nitrate. Surfactin was added to HAuCl4, followed by a dropwise addition of sodium borohydrate mixture. These nanoparticles exhibit various physical, chemical, magnetic, and structural characteristics. Various pH and temperature settings were tried. Surfactin was utilized to stabilize the nanoparticles for two months. Surfactin is a low-toxicity, renewable, and biodegradable stabilizer, and an ecologically beneficial ingredient.
Rhamnolipids have been examined for their influence on zirconia nanoparticles' electrokinetic and rheological behavior [88]. As indicated by zeta potential studies, the biosurfactant adsorbed zirconia particles with increasing concentration and could scatter the zirconia particles above pH 7.
Biosurfactants have a variety of roles, including hydrophobic water insoluble substrate bioavailability, increased surface area, metal-binding property, quorum sensing, bacterial pathogenicity, biofilm destruction, and so on. This diverse behavior of biosurfactants, diverse chemical groups, and diverse structures have opened the gate to many fields. In the medical field, they are popular due to their broad range of structures, and antimicrobial properties, antibacterial properties. Some act as drug delivery agents, and interact with pathogens. In comparison, biocompatibility and digestibility allow them to play a crucial role in the cosmetics and food industries [89]. Surfactants are synthetic/ chemically available, but nowadays, biosurfactants are replacing them. Chemically synthesized surfactants are non-biodegradable and toxic to human health as well as to the environment; therefore, this chapter discusses the surfactants of microbial origin and their applications in healthcare.
Many yeasts and bacteria grow on n-alkanes, contributing to fatty acids, phospholipids, and neural lipids. Lipopeptides and lipoproteins involve gramicidin as lipopeptides and polymyxins as lipopeptide antibiotics. Polymeric biosurfactants, such as emulsan, liposan, mannoprotein, and polymeric protein complex, are also available. Microemulsions are formed by particulate biosurfactants, which are crucial for alkane uptake by microbial cells [90, 91].
Biosurfactants show different biological activities, such as the inhibition of bacterial growth, toxic effects on harmful cells, tumor growth inhibitors, antibiotics, cell lysis, fungicidal properties, food digestion, anticancer agents, antibiofilm agents, antiadhesive agents, etc. Some of these activities, along with microorganisms, are mentioned in Table 2.
Biosurfactants as Antimicrobial Agents
Literature reports much experimental evidence, i.e., research and reviews of the antimicrobial activities of various biosurfactants. It is ubiquitous to use antimicrobial agents to cure bacterial infections, but the constant use of these different kinds of antibiotics has created resistance in the microbial community. Resistance organisms generate antimicrobial-resistant strains or bacterial resistance strains by natural processes such as conjugation, transformation, or transduction. These medicines work by inhibiting the cell wall, and nucleic acid or protein, interfering with metabolic pathways, or damaging the bacterial membrane. While resistant bacteria defend themselves against antimicrobial compounds by diverse mechanisms such as enzymatic degradation, target modification, inactivation, or change of antimicrobial substances [105, 106]. Biosurfactants, such as Lactococcus lactis 53 and Streptococcus thermophilus A, have recently been widely employed as antimicrobial agents, even in low concentrations against the yeast Candida tropicalis GB9/9, which is responsible for prosthesis failure. When these were tested in high concentrations, both were highly active against different bacterial and yeast cells [107].
In another study, it was found that biosurfactants-producing lactobacilli which are probiotically active help in maintaining a healthy gut or intestinal tract as well as protect against pathogens [108]. In vivo investigations have demonstrated that lactobacillus plantarum 299v and lactobacillus rhamnosus GG (both probiotic strains) may prevent E. coli adherence to intestinal epithelial cells by expressing mucin, implying that they do so through creating biosurfactant [13
