The Enhanced Biodegradation of Petroleum Lubricant by Bacterial Strains Harvested From Oil Contaminated Soil

Up to now, little information has been available on biodegradation of petroleum lubricant oils by microbial inoculation. Understanding the abilities of microorganisms in biodegrading petroleum lubricants is imperative for optimum use of bacteria in bioremediation of lubricant-contaminated environments. In the study, three bacterial strains of genera Pseudomonas sp., Ochrobactrum tritici, and Bordetella petrii, which were previously isolated from oil-contaminated soils, were inoculated into a lubricating oil culture medium. The abilities for the three bacterial strains to biodegrade a petroleum lubricating oil were evaluated by determining the chemical oxygen demand (COD) of the inoculated oil culture mediums. Effect of pH on degrading abilities of the bacterial isolates and impact of temperature on microbial growth were also explored. Results showed that the CODs of the inoculated lubricating oil culture mediums were much lower than that of the oil medium without bacterial inoculum, indicating that the three bacterial strains effectively enhanced biodegradation of the mineral lubricating oil, of which the member of genus Ochrobactrum was the most excellent enhancer. Furthermore, the abilities for the strains to biodegrade lubricating oil were different at different pH values. They provided excellent oil-degrading ability in the pH range from 6.0 to 7.8. On the other hand, the microbial populations of the bacterial strains markedly increased with increasing incubation durations in an exponential phase at the temperatures ranging from 28 degrees C to 35 degrees C.