Exploring the bioremediation capacity of Bacillus and Pseudomonas species isolated from mechanic workshop soil

Spent engine oil contamination resulting from mechanical workshop activity poses a significant environmental challenge due to the undegraded petroleum hydrocarbon, toxic additives and heavy metal in the environment. This study evaluated the biodegradation potential of indigenous Pseudomonas and Bacillus species isolated from spent engine oil contaminated mechanical workshop soils in Abakaliki. Ebonyi State, Nigeria. A total of 88 (100%) bacterial isolates were recovered from the contaminated soil, from which 16 (18.18%) hydrocarbon-utilizing isolates were selected following turbidity/growth screening for biodegradation studies. The isolates were characterized using standard morphological and biochemical methods and was evaluated for their ability to degrade spent engine oil in Mineral Salt Medium over a 21-day incubation period. Biodegradation efficiency was determined gravimetrically. While Gas Chromatography - Mass Spectrometry (GC-MS) was employed to evaluate changes in hydrocarbons composition. After a period of 21 days, Pseudomonas SA/B81 and Pseudomonas SA/A51 achieved about 78% and 75% degradation respectively while Pseudomonas SB/A83 only achieved a 3% degradation. Among the Bacillus species Bacillus isolate SA/B75, SA/B62 and SB/B74 achieved degradation efficiencies of 54%, 46% and 40% respectively. GC-MS analysis revealed a reduction in hydrocarbon compound from eighteen in the untreated spent engine oil to eight after biodegradation by Pseudomonas SA/B81. Several hydrocarbon constituents (Eicosanoic acid, tetratriacontane, 1, 2,3-trimethylbenzene) were completely eliminated, while the remaining compounds (Octadecanoic acid, octadec-9-enoic acid) were detected at reduced level, indicating extensive microbial transformation, few of the persistent residual compounds suggest the presence of recalcitrant hydrocarbon fractions or intermediates biodegradation requiring further investigation. These findings demonstrate that indigenous Pseudomonas SA/B81 possesses promising potential for bioremediation of spent engine oil and maybe beneficial for bioremediation of polluted environment. Further study should incorporate molecular identification and field-scale validation. Indigenous Bacillus and Pseudomonas species were isolated from contaminated mechanical workshop soils. Sixteen bacterial isolates were screened for spent engine oil biodegradation. Pseudomonas isolate SA/B81 achieved the highest degradation efficiency of 78% after a period of 21 days. GC-MS analysis confirmed substantial reduction in hydrocarbon constituents following biodegradation.