Rhizosphere Associated Bacteria in Bioremediation of Crude Oil Polluted Aquatic Environment

Aim: This study was conducted to examine the biodegradation of crude oil by microorganisms isolated from rhizosphere soil of plants found in an oil polluted aquatic environment. Study Design: Laboratory scale broth microcosms was adopted. Place and Duration of Study: Study was done in Department of Environmental Management and Toxicology, Federal University of Petroleum Resources, Effurun/six months. Methodology: Hydrocarbon utilizing bacterial species were isolated from the rhizosphere soil of plants from a crude oil polluted soil. They were screened for hydrocarbon degradative abilities and identified. Isolates with the best degradative capabilities were used for the bioremediation studies. Microcosms contained 5mls of crude oil (5% volume per volume (V/V)), 100mls of mineral salt and 10mls of isolates (10% V/V). Degradation was evaluated by changes in pH, microbial counts, residual oil and grease. Results: Ten bacterial isolates were isolated and identified as Pseudomonas, Bacillus, Proteus, Enterobacter, Escherichia and Staphylococcus. Pseudomonas, Bacillus, Proteus were used for the biodegradation experiment. Residual oil and grease values were 1.308mg/l, 2.344mg/l and 2.578mg/l for Pseudomonas, Proteus and Bacillus in set-up; suggesting they could degrade crude oil using it as carbon source. Pseudomonas species performed the most while the control had a value of 3.533mg/l at the end of study. Hydrocarbon utilizing bacterial counts during the assay increased. The bacterial counts were in the increasing sequence; control (3.5×105 CFU/ml), Bacillus (2.05×106 CFU/ml), Proteus (2.28×106 CFU/ml) and Pseudomonas (2.85×106 CFU/ml). Conclusion: Results indicated that rhizosphere soil of plants in an oil polluted environment could be a ready source of hydrocarbon utilizing bacteria. Microbial communities exposed to hydrocarbons become adapted, exhibiting selective enrichment and genetic changes, resulting in increased proportions of heterotrophic hydrocarbon-degrading bacteria.