Potential petroleum degrading bacteria, Pseudomonas aerogenosa and Micrococcus sp. was isolated from petroleum contaminated soil in petroleum microbiology laboratory, Department of Microbiology University of Nigeria, Nsukka. Hydrocarbon utilization in liquid media was assessed through time – course optical density measurement. Concentrations of the heavy metals ranging from 50 to 200 mg/L were introduced into 100 ml of mineral salt medium containing 10 ml of kerosene inoculated with P. aeruginosa or Micrococcus sp. and incubated at room temperature (25-30°C) for 384 h. Control samples contained kerosene but no heavy metals. At low concentrations the heavy metals significantly (p <0.05) improved the growth of the isolates as indicated by the highest OD600 obtained with 50 mg/L of the metals which was the lowest concentrations. This was confirmed by the bacterial cell number extrapolated from an OD standard curve. At higher concentrations of the heavy metals (150 to 200 mg/L) there was a decline in the growth rates of the isolates. The effects of the heavy metals on the hydrocarbonoclastic efficacy of the isolates were dose-dependent and their growth rates in the presence of the metals were in the following order: Lead > Cadmium > Mercury.
Key words: Heavy metals, kerosene, bioremediation, bacteria.
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