Isolation, screening and molecular characterization of biosurfactant producing bacteria from soil samples of auto repair shops.

A total of 107 bacterial strains were isolated from used motor oil contaminated soil samples from auto-repair shops. The isolates were evaluated for their biosurfactant production abilities by employing a series of screening techniques, including hemolytic assay, oil displacement assay, drop-collapse assay, and parafilm M test. The potential biosurfactant producers were characterized by 16S rDNA-based molecular tools and were identified as Proteus mirabilis, Klebsiella pneumoniae, Enterobacter cloacae, Micrococcus sp., Citrobacter sp., and Bacillus sp. The widest clearing zone with a diameter of 6.5 cm was observed upon the addition of cell-free supernatant (CFS) from P. mirabilis SLM-B52 as assayed by the oil displacement test. Remarkable emulsification indexes, equivalent to 42% (against kerosene), 53% (against xylenes), and 50% (against benzene and toluene), were recorded by the CFSs of Micrococcus sp. SLM-B28, P. mirabilis SLM-B85, and K. pneumoniae SLM-B46, respectively. Du Noüy tensiometer analysis showed that biosurfactant produced by P. mirabilis SLM-B52 has the highest surface tension reduction capacity with a value of 30.5 mN m. The emulsifying activity of a CFS from P. mirabilis was also described in this study for the first time. Taking together, biosurfactants from promising bacterial strains have potential application in microorganism-based biodegradation processes of hydrocarbons which cause detrimental effects on the environment.