Bio-surfactants are a chemically unique class of compounds produced by many bacteria and fungi and are used in bioremediation.
In terms of chemical structure, bio-surfactants can be divided into several broad groups – glycolipids, lipopeptides, lipopolysaccharides, phospholipids and neutral lipids/ fatty acids.
Generally their molecular weights range from about 500-1500, although so many have molecular weight up to 14300. Few bio-surfactants have been well studied with respect to remediation.
The best – studied bio-surfactant is rhamnoUpid produced by Pseudomonas spp. Some information is also available regarding Bacillus- surfaction, Rhodococcus – trehalose lipid, and Candida- sophrorose lipid systems. Procedures for testing the effect of any surfactant (either synthetic or biological) on solubilization and biodegradation of model hydrocarbons have been described (Miller and Zhag, 1997).
Bio-surfactants are not yet available commercially and therefore must be produced in the laboratory. For example, rhamnolipids can be produced and recovered from many Pseudomonas aeruginosa strains. Protocols for production, purification and use of a number of bio-surfactants have been developed.
Hydrocarbon biodegradation can be determined by measurement of hydrocarbon mineralization or by measurement of protein increase as an indication of cell growth. The solubilization of hydrocarbons by surfactants is markedly affected by environmental conditions. One common way to measure biodegradation is to measure substrate disappearance.
Surfactants do not confer degradative ability; instead, they aid in increasing mass transfer of hydrocarbons into the aqueous phase and they may possibly aid in delivery of hydrocarbons to cells. However, the behaviour of surfactants in soil systems needs to be investigated further. In this case, the effect of bio-surfactant sorption by soil must be considered because sorption can significantly reduce the effective amount of bio-surfactant available in solution. Thus, much higher bio-surfactant concentrations may be required in such cases.