Biosurfactants: Microbial Origin

The water-soluble compounds are preferred source of nutrition for microbial growth. The nonaqueous phase soluble hydrocarbons, although are rich source of carbon and energy for microbial growth, are not readily bioavailable to microorganisms. Some of the microbial populations present in such ecosystem produce surfaceactive compounds which help in emulsification of these nonaqueous phase hydrocarbons to aqueous phase. The microemulsions of hydrocarbons thus formed increase their availability to microbes which can use them as growth substrates. This ability of these microorganisms provides them a competitive edge over nonbiosurfactant-producing microbes to thrive in oligotrophic environment. The microorganisms belonging mainly to Pseudomonas spp., Rhodococcus spp., Arthrobacter spp., Bacillus spp., etc. are being explored for production of surface-active molecules for diverse applications.

Classification and Chemical Composition

Biosurfactants are natural surface-active secondary metabolites of microbial origin which are known for their diverse chemical structures (Fig. 18.1). The surfaceactive compounds of microbial origin are primarily classified into two major classes: biosurfactants (low-molecular-weight compounds) and bioemulsifiers (highmolecular-weight compounds). Microbial surfactants are amphipathic biomolecules having both hydrophobic and hydrophilic domains. The hydrophilic domain can be a carbohydrate, phosphate, cyclic peptide, amino acid, carboxylic acid, or alcohol. Most of the biosurfactants are either anionic or neutral while some are cationic, having amine groups. The hydrophobic moiety is frequently a hydrocarbon chain comprised of a long-chain fatty acids, hydroxy fatty acids, or α-alkyl-β-hydroxy fatty acids. These wide ranges of structural variations in biosurfactants provide them characteristic surface-active properties, ranging from emulsifiers to biosurfactants, which could be exploited for multifarious applications. The broad grouping of structurally diverse biosurfactants and their microbial origin are summarized in Table 18.1.

Fig. 18.1 Structural variations in different types of microbial surfactants

Comparative Account of Biosafety and Surface-Active Properties of Biosurfactants and Synthetic Surfactants

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