Biosurfactants (microbial surfactants) are surface-active substances that are biosynthesized by living cells including animals and microorganisms. They are surfactants synthesized by microbes especially bacteria, yeasts and moulds. Biosurfactants-producing bacteria are widely distributed in natures especially in undisturbed and contaminated soils. Biosurfactants are important biological molecules that have applications in a wide variety of commercial sectors including but not limited to agriculture, medicine, food industry, waste control/management, environmental pollution control, and production of cosmetics, oil-recovery systems/oil industry, bioremediation and other industrial applications. Some microbial surfactants possess antimicrobial activity, and thus could be used as antimicrobial agents. Biosurfactants also play significant roles in the growth and survival of the microorganisms that secrete or produce them. Like surfactants, biosurfactants also possess a hydrophilic head (water-loving group) and a hydrophobic tail (water-hating tail) – which act in consortium to reduce the surface tension and interfacial tensions that exist between individual molecules at the surface and interface respectively. A large variety of microorganisms including yeasts, moulds and bacteria produces biosurfactants, and these potent surface-active agents vary in their chemical properties and molecular size. The low molecular weight surfactants are often glycolipids while the high molecular weight surfactants are generally either poly-anionic hetero-polysaccharides containing covalently-linked hydrophobic side chains or complexes containing both polysaccharides and proteins.
The surface active agents synthesized by microbes are mainly composed of glycolipids, peptides, lipoproteins, fatty acids, glycopeptides and phospholipids. Several factors affect the production of microbial surfactants by microbes. Biosurfactant production solely depends on the type of carbon source present in the organism’s environment and also on the types and amounts of other growth nutrients available. In order words, the yield of the biosurfactant greatly depends on the nutritional environment of the growing organism. The nutrients available to the biosurfactant-producing microbe will determine whether or not the biosurfactant is produced; and when finally produced, it will also influence the composition of the surface-active agent produced. Though the type and amount of the microbial surfactants produced depend primarily on the producer organism and its carbon source, factors like nitrogen, trace elements, temperature, and aeration also affect microbial surfactant production by the organism. Biosurfactants offer many advantages over the chemically synthesized surfactants. Biosurfactants are less-toxic than surfactants. They have good biodegradability and biosurfactants are more eco-friendly than the chemically synthesized surfactants.
Biosurfactants can withstand extreme or harsh environmental conditions and they can be produced in large scale by microbes. They enhance the emulsification of hydrocarbons, and thus have the potential to solubilize hydrocarbon contaminants in the soil and increase their availability for further microbial degradation. Microorganisms that produce microbial surfactants (biosurfactants) play an important role in the accelerated bioremediation of hydrocarbon-contaminated sites or soils especially during oil spillage. And the use of biosurfactants to clean up oil-contaminated sites is more eco-friendly than the use of chemically synthesized surfactants. The use of chemicals for the treatment of a hydrocarbon polluted site or soil may contaminate the environment with their by-products. But this is not the case for microbial surfactants – in which biological treatment efficiently destroy the pollutants, while being biodegradable in the process. Several microorganisms including bacteria, yeasts and moulds are known to synthesize microbial surfactants; and when provided with the necessary growth medium or environment, these microbes can synthesize a wide range of microbial surfactants that has applications in many commercial sectors (Table 1).
Table 1: Microorganisms that produce biosurfactants
Thiobacillus sp, Mycobacterium sp, Nocardia sp, Arthrobacter sp, Corynebacterium sp, Micrococcus sp, Penicillium sp and Aspergillus sp are other examples of microbes that produce biosurfactants. Glycolipids are the most widely used class of biosurfactants.
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