Isolation, Screening and Characterization of Hydrocarbon-Utilizing Bacteria Isolated from Bitumen-Contaminated Surface Water in Agbabu, Ondo State

Abstract

Surface water samples from contaminated surface water in Agbabu, Odigbo Local government area of Ondo State were analyzed for hydrocarbon-utilizing bacteria. The mean total bacterial count and mean total hydrocarbon- degrading bacterial counts were determined using pour plate technique. The hydrocarbon-utilizing potentials of the isolates were further determined by screening them in minimal salt broth supplemented with 2% crude-oil over a period of 14 days. The growth of the isolates was monitored by measuring the absorbance (OD600 nm) and Total viable count (log10 CFU/ml). The effect of temperature, pH and crude-oil concentration on their degradative potentials was determined. The isolates were identified based on their cultural, morphological and biochemical characteristics according to Bergey’s Manual of Systematic Bacteriology. The Mean Total bacteria count was 7.70 (log10 CFU/ml) ranging from 6.25  to 8.77  (log 10 CFU/ml) while the Mean Total hydrocarbon-utilizing bacteria was 7.14 (log10 CFU/ml) ranging from 4.77 to 7.64   (log10 CFU/ml). Six  bacteria genera isolated from the samples collected include: Staphylococcus, Micrococcus, Pseudomonas, Enterobacter, Bacillus and Alkaligens. Five isolates namely; Pseudomonas aeruginosa, Bacillus cereus, Bacillus lichenformis , Micrococcus luteus and Alkaligens faecalis showed maximum utilization of crude-oil as sole carbon source and were selected for further studies. The result of varying crude-oil concentrations (1.0 -2.5%) on each of the selected hydrocarbon-utilizing bacteria showed that the isolates grew optimally at  2% crude-oil concentrations where two  of the isolates B. cereus and P. aeruginosa had the highest growth rate of 0.77 and  0.75 respectively. However, their growth gradually reduced at increased crude-oil concentration (2.5%).The growths of the isolates were optimal at neutral to alkaline pH (7-9) while their growths were greatly reduced at acidic pH 3. The optimum temperature for the growth of the isolates ranged between 40°C-45°C.The result from this research affirms that an effective utilization of crude-oil would require simultaneous action of several metabolically versatile microorganisms under favorable environmental conditions such as pH, temperature  and availability of nutrient.