Bioremediation of Crude Oil-Contaminated Soil Using Indigenous Hydrocarbon-Degrading Bacteria from Imo State

Crude oil spills from pipeline vandalism and operational discharges in Imo State, South East Nigeria, have degraded agricultural land and ecosystems in oil-producing communities. This study evaluates the bioremediation potential of hydrocarbon-degrading bacteria isolated from chronically contaminated soils in Ohaji-Egbema Local Government Area for treating fresh crude oil contamination. Indigenous bacteria were isolated, screened for hydrocarbon utilisation on mineral salt agar with crude oil as the sole carbon source, and identified by 16S rRNA gene sequencing. Three selected isolates, identified as Pseudomonas putida, Bacillus subtilis, and Alcaligenes faecalis, were evaluated for bioremediation of crude oil-spiked soil at 50,000 mg/kg total petroleum hydrocarbons in microcosm experiments over 60 days, individually and as a consortium, with and without NPK nutrient amendment. Total petroleum hydrocarbon reduction was determined by Soxhlet extraction and gravimetric analysis at 15-day intervals. The bacterial consortium with nutrient amendment achieved the highest total petroleum hydrocarbon reduction of 78.4% at 60 days, compared to 43.2% in the unamended consortium treatment and 8.1% in the unaugmented control. Soil enzymatic activities increased progressively in augmented treatments, indicating microbial metabolic recovery. The findings establish a locally sourced, low-cost bioremediation strategy for crude oil-impacted soils in South East Nigeria. Keywords: bioremediation, crude oil, hydrocarbon-degrading bacteria, Imo State, soil contamination