ISOLATION OF BIOSURFACTANT-PRODUCING BACTERIA FROM OIL-SPILLED SOIL AND CHARACTERIZATION OF THEIR SECRETED BIOSURFACTANTS IN PATHOGEN-INHIBITION AND OIL-EMULSIFICATION

Microbial biosurfactants are surface-active amphiphilic molecules produced by bacteria, yeast and fungi. Biosurfactant-producing bacteria, often recovered from oil-polluted sites, have significant role in microbial enhanced oil recovery (MEOR), environmental sustainability and pharmaceutical applications. The objective of the present study includes isolation, screening and selection of biosurfactant-producing bacteria from oil polluted sites and characterization of their secreted biosurfactant. To this end, nine bacterial strains were isolated from oil spilled soil in a motor garage and subjected to blood hemolysis test as the preliminary screening for biosurfactant-producing strains wherein six isolates tested positive. Upon subsequent analysis by the oil spreading assay and emulsification index, two potent biosurfactant-producing strains were selected for further characterization. An extensive biochemical, cultural and morphological investigations identified the biosurfactant producing isolates as Bacillus species strain JR3 and Acinetobacter sp. strain JR7. Culture conditions of the two strains were optimized for maximum biosurfactant production. Their secreted biosurfactants were extracted from cell-free culture supernatant using chloroform-methanol precipitation, and characterized by thin layer chromatography which indicated that the biosurfactants were of lipopeptide in nature. The biosurfactants exhibited antimicrobial activity against both Gram positive and negative bacteria. Kerosene appeared to be the most suitable substrate for emulsification of the biosurfactants followed by diesel, soya bean, and octane. The thermal and pH stability of the extracted biosurfactants was assessed as a function of their emulsification index which indicated their stability under high temperature and a broad range of pH, suggesting their potential values in medicine, pharmaceutical and bioremediation under wide environmental conditions.