In this work, the degradative abilities of some bacteria isolated from the soil were studied. Five distinct isolates were subjected to substrate susceptibility test to determine their potential degradative abilities in the presence of different hydrocarbons. The best three crude oil degraders were selected and their identities were further established using API technique. Furthermore, the extent of each degradative ability of the three bacteria was determined using gas chromatography (GC) technique to analyze the residual crude oil after 21 days. The pH and total viable counts (TVC) were also monitored every three days for the period of the study. The three isolates were later subjected to plasmid extraction and the cured isolates were again exposed to crude oil. The initial bacteria isolated were; Pseudomonas cepacia (B1), Micrococcus luetus (B3) Bacillus coagulans (B4), Citrobacter koseri (B2) and Serratia ficaria (B5). C. koseri, S. ficaria and B. coagulans had strong growth in crude oil. B. coagulans was able to degrade 95% of the crude oil; S. ficaria degraded 92% of the crude oil, and C. koseri degraded 91% of the crude oil using it as the sole carbon source. The pH was relatively the same throughout the period and the TVC that were initially low for the three bacteria, later increased. Degradative abilities of B. coagulans and C. koseri were chromosomal mediated while S. ficaria was plasmid mediated. The biological/genetic basis of their degradative activities can be used improve their degradative abilities.

Laboratory studies were developed to compare the effectiveness of inoculated bacteria consortia and indigenous microorganisms on diesel-polluted soil for 18 days. Bacteria isolated from the unpolluted soil sample were: Pseudomonas spp. (LBI), Pseudomonas cepacia (LB5), Micrococcus luetus (LB2), Bacillus subtilis (LB3) and Bacillus cereus (LB4). Their ability to degrade different substrates were first studied by the presence of growth in minimal salt broth. All the isotates were unable to grow in hexane. LB1 and LB2 had a strong growth in n-dodecane and n-hexadecane. Only LB1, LB4 and LB5 were able to grow in paraffin. LB1 and LB5 had poor growth on xylene. LB1 and LB3 had moderate growth in phenol. All the isolates had little growth in kerosene and only LB3 and LB4 grow in diesel. The three most promising of the isolates, with moderate to strong growth (LB2, LB4 and LB5) on crude oil were further used for diesel bioremediation. The bacterial population in the augmented diesel-contaminated soil showed a reduction in the population density from days 15 to 18, an indication of nutrients (diesel oil) exhaustion. While the un-augmented diesel-polluted soil samples showed potential of more days of increased bacterial population after the 18th day of observation, a pointer of more diesel in the soil samples that can be metabolized/utilized by the microorganisms present in soil samples. The consortia of Bacillus coagulans, Citrobacter koseri and Serratia ficaria was effective in the removal of 73.8% diesel oil from the diesel-polluted soil sample while natural attenuation resulted in 41.0% diesel oil removal and 35.8% in the control.

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