Abstract
A study was carried out in a screen house to determine the bacterial population dynamics in a crude oil soil undergoing bioremediation. The agricultural soil samples were polluted with different concentrations (5, 8 and 11%) of crude oil. Physiochemical and microbiological analyses were carried out on the polluted and unpolluted soil samples at various intervals beginning from two weeks after the pollution of the soil samples to the fourteenth week. The soil samples were found to be acidic (5.40) and rich in phosphorous (26.52 mg/kg). There were no significant differences in the pH, organic matter, sodium, potassium and magnesium of the unpolluted and the polluted soil samples. The microbial loads of the polluted soil samples were lower than the unpolluted soil samples throughout the study. The highest bacterial loads (27.00d±2.20, 19.40c±1.80, 8.70b±0.50 for 5, 8 and 11% crude oil concentration respectively) were observed, when Ewingella americana (bacterium with known crude oil degrading ability) was inoculated into the polluted soil samples. The bacterial species responsible for the bioremediation from the polluted soil samples were identified using conventional techniques. The bacterial species isolated and identified were Pseudomonas aeruginosa, Bacillus subtilis, Bacillus cereus, Proteus vulgaris and Staphylococcus aureus. Bacillus spp has the highest percentage frequency (Bacillus subtilis = 30.95% and Bacillus cereus = 21.43%). The consistent isolation of these bacteria shows that they could survive the crude oil pollution and possibly utilize the crude oil, thereby making the crude oil less harmful to the environment. Key words: Bacteria, bioremediation, bacterial species, crude oil.
Highlights
Crude oil is the major source of energy for industries and homes
The aim of this study was to inoculate crude oil polluted soil with known bacterium with a high biodegradative ability obtained from previous research work, and monitor the bacterial population dynamics of MATERIALS AND METHODS
The highest values of bacterial loads were observed after broth culture of E. americana with known crude oil degrading ability was inoculated into the polluted soil samples and there was a sharp fall in the microbial load afterwards, which could have resulted from bacterial competition between the indigenous bacteria and the inoculated bacterium for hydrocarbons in the polluted soil samples as source of carbon, for nutrients and energy
Summary
Crude oil is the major source of energy for industries and homes. Crude oil and petroleum products are very complex and consist of mixtures of thousands of individual compounds that exhibit a wide range of physical properties (Leahy and Colwell, 1996). Petroleum may be classified into four major groups based on their different solubility in organic solvents and their chemical composition (Leahy and Colwell, 1996) They are saturated and unsaturated hydrocarbons, which are usually the most abundant constituents in crude oils. Examples of species of aerobic bacteria recognized for their degradative abilities are Pseudomonas, Alicaligenes, Sphingomonas, Rhodococcus and Mycobacterium, Bacillus, Flavobacterium. These microbes have often been reported to degrade pesticides and hydrocarbons, both alkanes and polyaromatic compounds. Other examples of bacteria that have been implicated in crude oil biodegradation include; Alicaligenes, Sphingomonas, Rhodococcus, Mycobacterium and Flavobacterium (April et al, 2000; Okoh and Ezeronye, 2002; Zhang et al., 2006). The aim of this study was to inoculate crude oil polluted soil with known bacterium with a high biodegradative ability obtained from previous research work, and monitor the bacterial population dynamics of
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