INFLUENCE OF PLASMIDS ON MICROBIAL DEGRADATION OF CRUDE OIL IN CONTROLLED GROWTH SYSTEMS

This study evaluated the role of plasmid-mediated biodegradation of crude oil by indigenous soil bacteria under optimized growth conditions. Standard microbiological techniques including enrichment culture, turbidometric assay, antimicrobial susceptibility testing, plasmid curing, and biodegradation optimization were employed. Out of the isolates examined, 22 demonstrated significant crude oil-degrading potential, indicated by absorbance values (A₆₀₀nm > 0.3), confirming their ability to utilize crude oil as a sole carbon source. Plasmid curing tests revealed that isolates C1, D1, L2, and J3 retained partial growth after plasmid removal, whereas isolates G2, H4, K4, and I6 lost the ability to grow, suggesting plasmid dependency for crude oil degradation. Antimicrobial susceptibility patterns further showed that plasmid-bearing isolates were resistant to multiple antibiotics before curing but exhibited approximately 95% sensitivity post-curing. The crude oil-degrading bacteria were identified as members of the genera Bacillus, Pseudomonas, Ochrobactrum, and Enterobacter. Optimal biodegradation occurred under conditions of neutral pH, 35 °C temperature, and 3% crude oil concentration. These findings highlight the importance of plasmid-encoded traits in hydrocarbon degradation and antibiotic resistance, and suggest that such bacteria hold significant promise for bioaugmentation and the bioremediation of crude oil-contaminated environments.