Hydrocarbons Degrading Potential of Stimulated Cultures of Bacteria Isolated from Humic Fresh Water Sediment of Eniong River in the Niger Delta of Nigeria

Abstract

The Hydrocarbons degrading potential of stimulated cultures of bacteria isolated from humic fresh water sediment of Eniong River in the Niger Delta of Nigeria was studied. Preliminary screening of the humic hydrocarbonoclastic bacterial isolates revealed that among the 5 bacterial isolates (HSC1, HSC2, HSC3, HSC4 and HSC5), isolate HSC1 exhibited the strongest ability to utilize crude oil and was characterized to be Bacillus subtilis. In-vitro analysis of crude oil utilization of Bacillus subtilis- HSC1 when energized with various concentrations of sugar (glucose and sucrose) revealed variable levels of hydrocarbons utilization by monoculture of B. subtilis and enhanced degradation with biostimulation. The results of indirect assessment using the total viable cells revealed that the microbial biomass increased over time during degradation. The rate of increase was apparently higher in cultures stimulated with various concentrations of sugar (glucose and sucrose) than in the control and best growth were recorded on the 12th day when treated with 10% of glucose. Analysis of the optical density of the Bacillus subtilis during the degradation process revealed that the optical density increased with time. The pH of the test substrates decreased over time indicating a higher catabolic activity. The increase in acidity was higher in 15% and 20% glucose supplemented medium. The nutrient addition increased the bacterial cell numbers, optical density as well as the acidity (high decrease in the pH) of the test media between days 9 and 15 when compared with the rate derived from the test medium. In vitro degradation study carried out for the 15 days showed that, the degradation of crude oil and its component by B. subtilis was faster when stimulated with the different concentrations of sugar than when un-stimulated. The result showed a remarkable reduction in the total petroleum content of the test substrates treated with glucose and sucrose. The best results were obtained by treatment with 1 and 5% levels of the stimulants. At this level, the TPH content was reduced from 15.81 mg/kg observed for the control to 10.19 mg/kg (49.92% degradation) and 8.03 mg/kg (60.52% degradation) obtained from substrates stimulated with 5% glucose and 1% sucrose respectively. The high hydrocarbon degradation by stimulated culture of Bacillus subtilis- HSC1 implies that biostimulation can be harnessed for bioremediation purposes.