Studies on biodegradation of petroleum hydrocarbons by a soil bacterium

Abstract

The increased generation of petroleum hydrocarbon waste has been stated as one of the most critical environmental problems. Though microbial bioremediation has been widely used for waste treatment but their application in petroleum hydrocarbon waste treatment is limited since they have toxic effects on the microbial cells. newlineIn the present research work, soil samples from the petroleum contaminated sites were screened for petroleum hydrocarbon degrading microbes. Among the thirty two petroleum degrading bacteria, PS11 strain was selected for further work on the basis of highest zone of crude oil utilization. Phenotypic characterization and phylogenetic analysis confirmed strain PS11 to be Geobacillus stearothermophilus. The bacterial strain was able to grow in presence of petroleum hydrocarbons as evidenced by increase in cellular dry biomass after 6 h of incubation. However, PS11 cells exhibited a delayed growth pattern in the presence of crude oil in the growth medium in comparison to those growing in absence of crude oil. The strain was also capable to grow in presence of wide range of other hydrophobic solvents with log P-values between1-4,whereasalcohols having very low log P-value had inhibitory effect on growth. Transmission electron micrograph of PS11 cells grown in the presence of 10% (v/v) crude oil for 24 h showed convoluted cell membrane and accumulation of crude oil in the cytoplasm, indicating the adaptation of the bacterial strain to the petrol. The mechanism of solvent tolerance of PS11 was ascertained by gas chromatography analysis of metabolic transformation products of crude oil and other solvents as well as membrane phospholipids. Results showed that PS11 cells growing in presence of crude oil (10 % v/v) for 15 days could degrade both alkanes and aromatic compounds. It degraded aromatic compounds more readily than alkanes. The membrane phospholipids composition of G. stearothermophilus PS11 was also altered in the presence of crude oil. newline