Biosurfactants
Microorganisms synthesize a wide variety of high- and low-molecular-mass bioemulsifiers. The low-molecular-mass bioemulsifiers are generally glycolipids, such as trehalose lipids, sophorolipids, and rhamnolipids, or lipopeptides, such as surfactin, gramic
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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 Chemical and Surface Properties of Biosurfactants . . . . . . . 282 Glycolipids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 Lipopeptides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 Fatty Acids and Phospholipids . . . . . . . . . . . . . . . . . . . . . . . . . . 285 High-Molecular-Weight Biosurfactants . . . . . . . . . . . . . . . . . 285 Other High-Molecular-Mass Biosurfactants . . . . . . . . . . . . 286 Genetics and Regulation of Bioemulsifier Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 Lipopeptides of Gram-Positive Bacilli . . . . . . . . . . . . . . . . . . . 287 Rhamnolipids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 Polymeric Bioemulsifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 Natural Roles of Biosurfactants . . . . . . . . . . . . . . . . . . . . . . . . . 289 Increasing the Surface Area of Hydrophobic Water-Insoluble Substrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 Increasing the Bioavailability of Hydrophobic Water-Insoluble Substrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 Regulating the Attachment-Detachment of Microorganisms to and from Surfaces . . . . . . . . . . . . . . . . . . 289 Potential Commercial Applications . . . . . . . . . . . . . . . . . . . . . 290
Abstract Microorganisms synthesize a wide variety of high- and lowmolecular-mass bioemulsifiers. The low-molecular-mass bioemulsifiers are generally glycolipids, such as trehalose lipids, sophorolipids, and rhamnolipids, or lipopeptides, such as surfactin, gramicidin S, and polymyxin. The high-molecularmass bioemulsifiers are amphipathic polysaccharides, proteins, lipopolysaccharides, lipoproteins, or complex mixtures of these biopolymers. The low-molecular-mass bioemulsifiers lower surface and interfacial tensions, whereas the higher-molecular-mass bioemulsifiers are more effective at stabilizing oil-in-water emulsions. Three natural roles for bioemulsifiers have been proposed: (1) increasing the surface area of hydrophobic water-insoluble growth substrates, (2) increasing the bioavailability of hydrophobic substrates by increasing their apparent solubility or desorbing them from surfaces, and (3) regulating the attachment and detachment of microorganisms to and from surfaces. Bioemulsifiers have several important advantages over chemical surfactants, which should allow them to become prominent in industrial and environmental applications. The potential commercial applications of bioemulsifiers include bioremediation of oil-polluted soil and water; enhanced oil recovery; replacement of chlorinated solvents used in cleaning-up
oil-contaminated pipes, vessels, and machinery; use in the detergent industry; formulations of herbicides and pe
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