Biosurfactant

Biosurfactant usually refers to surfactants of microbial origin.^[1][2] Most of the biosurfactants produced by microbes are synthesized extracellularly and many microbes are known to produce biosurfactants in large relative quantities.^[3] Some are of commercial interest.^[4] As a secondary metabolite of microorganisms, biosurfactants can be processed by the cultivation of biosurfactant producing microorganisms in the stationary phase on many sorts of low-priced substrates like biochar, plant oils, carbohydrates, wastes, etc. High-level production of biosurfactants can be controlled by regulation of environmental factors and growth circumstances.^[5]

Classification

Biosurfactants are usually categorized by their molecular structure. Like synthetic surfactants, they are composed of a hydrophilic moiety made up of amino acids, peptides, (poly)saccharides, or sugar alcohols and a hydrophobic moiety consisting of fatty acids. Correspondingly, the significant classes of biosurfactants include glycolipids, lipopeptides and lipoproteins, and polymeric surfactants as well as particulate surfactants.^[6]

Examples

Phosphatidylcholine, also known as lecithin, is a pervasive biological surfactant. Shown in red – choline and phosphate group; black – glycerol; green – monounsaturated fatty acid; blue – saturated fatty acid.

Common biosurfactants include:

• Bile salts are mixtures of micelle-forming compounds that encapsulate food, enabling absorption through the small intestine.^[7]
• Lecithin, which can be obtained either from soybean or from egg yolk, is a common food ingredient.
• Rhamnolipids, which can be produced by some species of Pseudomonas, e.g., Pseudomonas aeruginosa.^[8]
• Sophorolipids are produced by various nonpathogenic yeasts.
• Emulsan produced by Acinetobacter calcoaceticus.^[4]
• Surfactin is a non-ribosomal lipopeptide produced by Bacillus subtilis

Microbial biosurfactants are obtained by including immiscible liquids in the growth medium.^[9]

Applications

Potential applications include herbicides and pesticides formulations, detergents, healthcare and cosmetics, pulp and paper, coal, textiles, ceramic processing and food industries, uranium ore-processing, and mechanical dewatering of peat.^[9][2][3]

Oil spill remediation

Biosurfactants enhance the emulsification of hydrocarbons, thus they have the potential to solubilise hydrocarbon contaminants and increase their availability for microbial degradation.^[10][11] In addition, biosurfactants can modify the cell surface of bacteria that biodegrade hydrocarbons, which can also increase the biodegradability of these pollutants to cells.^[12] These compounds can also be used in enhanced oil recovery and may be considered for other potential applications in environmental protection.^[13]