Contamination with petroleum and its products is an environmental threat in oil producing countries. Microbes have been used to clean up petroleum contaminated environments, which has been demonstrated to be an appropriate and more practical alternative compared to the mechanical and chemical techniques. In this study, crude oil degrading indigenous bacteria were isolated from soils around the oil exploration sites in Western Uganda and their efficiency of oil biodegradation and presence of the catabolic gene xylE in the isolates to relate with their biodegradation efficiency were determined. The organisms with oil degrading activity were screened by isolating them from crude oil supplemented mineral salts medium (MSM). The isolates were tentatively identified phenotypically and confirmed genotypically by 16S ribosomal ribonucleic acid (rRNA) gene sequencing. Hydrocarbon degradation in the culture fluids was analyzed by a gas chromatography mass spectrometer (GC/MS); and amplification of catabolic gene xylE by polymerase chain reaction (PCR) was done in order to relate with the degradation activity. Forty four indigenous oil degrading bacteria were isolated and categorized into eight groups based on their morphological and biochemical properties; and were identified as belonging to the genera; Corynebacterium, Pseudomonas, Moraxella, Bacillus, Enterobacteriaceae, Nocardia, Serratia and Rhodococcus. Eight isolates that exhibited a relatively higher biodegradation activity in the first five days of incubation were selected for a detailed analysis. Based on 16S rRNA gene sequence analyses, the eight selected isolates were identical to Stenotrophomonas maltophilia, Burkholderia sp., Delftia tsuruhatensis, Pseudomonas aeruginosa, Acinetobacter sp., Curtobacterium sp. and Paenibacillus agaridevorans. The selected isolates; Ngara-T1, Kig5-1, Kig5-T2, Kig3-T3, Kig3-T4, Kas2-T7, Kas2-T5 and Gat-3 degraded the total petroleum hydrocarbons (TPHs) up to: 91.9, 79.9, 89.2, 73.1, 94.2, 83.2, 77.0 and 67.2%, respectively, by the end of 21 days of incubation as compared to 29.7% degradation in the control experiment (without bacteria). The catabolic gene xylE was detected in two of the selected isolates, Ngara T-1 and Kig5-T2. It could be concluded that the oil degrading bacteria identified in this study showed diverse and varying capacities to degrade the crude oil; with some degrading up to 90% and can be exploited for cleaning up hydrocarbon contaminated sites in western Uganda.
Key words: Bacteria, bioremediation, degradation, oil, hydrocarbons, Uganda.