Crude oil biodegradation potential of lipase produced by Bacillus subtilis and Pseudomonas aeruginosa isolated from hydrocarbon contaminated soil

Microbial biodegradation of oil pollutants and their derivatives has become the most environmental-friendly method in the developing world. The aim of this study was to evaluate crude oil biodegradation potential of lipase produced by indigenous bacteria from oil contaminated soil. Indigenous bacteria isolates were identified as species of Bacillus subtilis and Pseudomonas aeruginosa, the isolates were able to produce lipase as revealed in their zone of clearance on tween 80 agar plates and the presence of lipase produced by the two bacteria were further confirmed using spectrophotometric analyses. Lipase produced by B. subtilis showed maximal lipase activity at pH 8 and 40$°C$ while the enzyme produced by P. aeruginosa showed maximal lipase activity (U/mL) at pH 8 and 50$°C$ when subjected to various pH and temperature respectively. Lipase produced by B. subtilis recorded 8.11 ± 0.70$\%$ of crude oil degradation in mineral salt medium within 28 days, while that of P. aeruginosa recorded 15.6 ± 0.03$\%$ of crude oil biodegradation. The GC–MS analysis of the crude oil treatment showed complete mineralization of several compounds, and also showed peak reduction which indicates lipase efficiency in the degradation of hydrocarbons. As revealed by GC–MS analysis, out of the 8 hydrocarbons identified in an undegraded oil, 5 were completely degraded by the enzyme activities while 2 (toluene and methyl, cyclopentane) were identified with hydrocarbons treated with lipase. The enzymes produced by B. subtilis and P. aeruginosa can serve as useful product for bioremediation of crude oil contaminated soil.