Biosurfactants are surface active molecules or chemical compounds synthesized by micro-organisms. These are amphiphilic compounds having both hydrophobic and hydrophilic domains. Biosurfactants are usually either anionic or neutral.
- The hydrophilic moiety can be a carbohydrate amino acid, or a phosphate group or some other compounds.
- The hydrophobic moiety is mostly long carbon chain fatty acid.
- Amphiphilic compounds are produced on living surfaces, mostly on microbial cell surfaces, or excreted extracellularly.
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| Emulsification of Biosurfactants molecules |
- The amphiphilic molecules confer the ability to accumulate between fluid phases, thus reducing surface and interfacial tensions at the surface and interface respectively. It Reduce surface and interfacial tensions in both aqueous solutions and hydrocarbon mixtures.
- This property of biosurfactants make them potential candidates for enhancing oil recovery.
Producers of Biosurfactants
A lot of microorganisms produce several classes of biosurfactants such as glycolipids, lipopeptides, phospholipids, neutral lipids or fatty acid and polymeric biosurfactants.- Several microorganisms are known to produce biosurfactants that can vary in structure and chemical composition. These variations depend on the producing microorganism and raw materials used.
- Biosurfactants are Produced during the growth of microorganisms on water soluble and water insoluble substrates.
- Micro organisms utilise a variety of organic compounds as the source of carbon and energy.
- When carbon source is an insoluble substrate like a hydrocarbon, microorganisms facilitate their diffusion in to the cell by producing a variety of biosurfactants.
- Some bacteria and yeasts excrete ionic surfactants which emulsify the CnHn substrates in the growth medium. Eg : rhamnolipids produced by different pseudomonas sp.
- Some other microorganisms are capable of changing the structure of their cell wall, which they achieve by synthesizing liposaccharides or non-ionic surfactants in their cell wall. Eg; Candida lipolytica and Candida tropicalis
Other effective biosurfactants are:
- Mycolates and Corynomycolates produced by Rhodococcus sp.,Corynebacteria sp., Mycobacteria sp., Nocardia sp.
- Ornithinlipids produced by Pseudomonas rubescene, Gluconobacter cerinus and Thiobacillus ferroxidans
Types of Biosurfactants
Biosurfactants are Categorised mainly by their chemical composition and microbial origin :
a) Low-molecular mass molecules
- Glycolipids
- Lipoproteins
- Phospholipids
- Polyanionic heteropolysaccharide.
a] Low-molecular mass molecules
This molecule has Efficiently low surface and interfacial tension.1).Glycolipids
- These are the most common biosurfactants.
- Glycolipids are conjugates of carbohydrates and fatty acids.
- Linkage is by means of either ether or an ester group.
- Eg. Rhamnolipids, Trechalolipids etc.
2).Lipopeptides and lipoproteins
- Lipopeptides and Lipoproteins Consists of a lipid attached to a polypeptide chain.
I). Surfactin
- Surfactin have superior surface activity and belongs to a group of cyclic lipoheptapeptides containing B-hydroxyl fatty acids and amino acid residues
- Produced by Bacillus sp.
- Bacillus licheniformis produces several biosurfactants which act synergistically and exhibit excellent temperature and pH and salt stability.
- Capable of lowering surface tension of water.
3). Fatty acid, phospholipids and neutral lipids
- Several bacteria and yeast produce large quantities of fatty acids and phospholipid surfactants during growth on n-alkanes.
- The amphiphilic balance id directly related to the length of the hydrocarbon chain in their structure.
b]. High-molecular mass molecule
These are the more effective emulsion stabilizing agents 1).Polymeric biosurfactants
- These are high molecular weight compounds
- Best studied polymeric biosurfactants are emulson, liposon, alasun, lipomannan and other polysaccharide-protein complexes.
- It is a complex extracellular acylated polysaccharide synthesized by the gram negative bacterium Acinetobacter calcoacetius
- An effective emulsifying agent for hydrocarbons in water.
Particulate Biosurfactants
These are of two types:1). Extracellular vesicles uptake -
- These partition hydrocarbons to form microemulsions which play an important role in hydrocarbon uptake by microbial cells.
- Whole bacterial cell act as surfactant.
Advantages of Biosurfactants
1. Biodegradability
- Biosurfactants are biodegradable in nature.
- Biosurfactants are able to broken down into more simple compounds by microbes through natural processes.
- Biosurfactants are environment friendly way and suited for bioremediation.
2. Low toxicity
- Biosurfactants are don't caue serious damage/harm of the biotic ecosystem since their toxicity level is low.
- They are non-toxic and on-mutagenic.
3. Biocompatibility and Digestibility
- Biosurfactants are well tolerated by living organisms.
- These when interact with living organisms do not change bioactivity of the organisms.
4. Availability of raw materials
- Biosurfactants can be produced from cheap raw materials like rapeseed oil, potato process effluent, oil refinery waste, cassava flour waste water, curd whey and distiller waste, sunflower oil etc. Which are available in large quantities.
- The carbon source may come from hydrocarbons, carbohydrates and /or lipids, which may be used separately or in combination with each other.
5. Acceptable production economics
- Depending on the application, biosurfactants can also be produced from industrial wastes and byproducts.
- This would be of particular interest for bulk production of biosurfactants which is economically acceptable.
6. Use in environmental control
- Biosurfactants are efficiently used in handling industrial emulsions, control of oil spills, biodegradation and detoxification of industrial effluents and in bioremediation of contaminated soil.
7. Specificity
- Being complex organic molecules with specific functional groups, are often specific in their action.
- This property used in detoxification of specific pollutants, de-emulsification of industrial emulsions, specific cosmetic pharmaceutical and food applications.
Disadvantages of Biosurfactants
- It is not produce at Large scale and as well as the products is very costly.
- Large quantities are particularly needed in petroleum and environmental applications, which, due to the bulk use may be expensive.
- Lack of obtaining pure substances which is of particular importance in pharmaceutical, food, and cosmetic applications.
Applications of Biosurfactants
1. Anti-adhesive agent
- Biosurfactants act as an anti adhesive agents.
- eg. surfactants from Streptococcus thermophilus, Pseudomonas fluorescens.
2. In food formulations
- In controlling agglomeration of fat globules, stabilization of aerated systems, improving texture and shelf life of starch containing products and improve consistency and texture of fat based products.
- Also used in bakery and ice-cream formulations where they act by controlling consistency, retarding staling and solubilizing flavor oils. Eg. rhamnolipids surfactants
3. Therapeutic and biomedical applications
- Antimicrobial activity - Eg: Pseudomonas aeruginosa Bacillus subtilis, Bacillus licheniformis, Candida antartica
- Anticancer activity - Eg: mannosylerythrintol, rhamnolipid, Sophorose lipid
- Anti-HIV and sperm -immobilising activity - Eg: sporolipid produced by Candid bombicola
4. Oil storage tank cleaning
- Biosurfactants used for reducing the viscosity of heavy oils, thereby facilitating recovers, transportation and pipelining.
- Eg: glycolipid
5. Biosurfactant used in mining
- Used for the dispersion of inorganic minerals in mining and manufacturing processes.
- Eg: biodispersan produced by Acinetobacter caleoaceticus.
6. Biosurfactants for agricultural use
- Maintaining soil health and protecting crops from various diseases.
- Low toxicity and biodegradability of biosurfactants have made these compounds superior to synthetic ones.
- They are used as biocontrol agents too.
- Needed for the hydrophilization of heavy soils to obtain good wettability and also to achieve equal distribution of fertilizers and pesticides in soils.
- Also used for formulating the poorly soluble organophosphorus pesticides.
- Biosurfactants used for the biodegradation of chlorinated pesticide and β endosulfan by 30%-40%.
- Eg: Bacillus subtilis
- Also mobilized the residual endosulfan isomers towards biodegradation.
Biosurfactants and Bioremediation
Bioremediation aims at providing cost effective, contaminant specific treatments to reduce or removal of the concentration of individual or mixed environmental contaminants.- The process of bioremediation can be carried out by utilizing plants microbes and or microbial products.
- Biosurfactants are used for the purpose of bioremediation.
- Biosurfactants in comparison to chemical surfactants have lower possible toxicity and shorter persistence in the environment. Eg: pseudomonas aeruginosa degrade polycyclic aromatic compounds.
Microbial Interaction with Pollutants
There is this three step mechanism for the uptake of pollutants by microbes- Uptake of pollutants dissolved in water
- Direct uptake of the pollutant from the liquid-liquid interface.
- Uptake of pseudosolubilized compounds.
Role of Biosurfactants in Bioremediation (How Biosurfactants are works?)
Two mechanisms through which microbial surfactants can enhance bioremediation are:- The increase of the substrate availability for microorganisms.
- Interaction with the cell surface to increase the hydrophobicity.
- Biosurfactants have the potential to promote the growth of bacteria on hydrocarbons.
- They do this by increasing the surface area between oil and water by emulsification, and by increasing pseudosolubility of hydrocarbons.
- Organic contaminants in soil have the tendency to be strongly adsorbed to soil particles. This can lead to extended remediation time.
- This time can be overcome through the application of biosurfactants. This relates to the process of mobilization
- The process of mobilization occurs at concentration below the CMC.
- At this concentration, biosurfactants reduce the surface and interfacial tension, thus increase the contact of biosurfactant with soil, oil systems.
- Solubilization occurs at concentration above CMC.
- At above CMC concentration the hydrophobic tails of microbial surfactants connect together inside the micelle, while the hydrophilic heads are directed towards the aqueous phase.
- They are also able to increase the hydrophobicity of degrading micro organisms, thereby facilitating cells to access hydrophobic substrates more easily. It will allow microorganisms to directly contact oil drops and solid hydrocarbons.
- Another aspect is the enhanced bioremediation of heavy metal contaminated sites.
- Heavy metals are nonbiodegradable and they can only be transferred from one chemical form to another, which will be less toxic or biodegradable.
- Biosurfactants form complexes with heavy metals. These complexes can be removed by washing process.
- Biosurfactants are efficient in the biodegradation of aliphatic and aromatic hydrocarbons.
