Assessment of the Microbial Diversity of Spent-Oil Contaminated Soil in Calabar, Nigeria

This study was designed to assess the total heterotrophic and hydrocarbon oxidizing microbial diversity, determine the physicochemical parameters of oil contaminated soil and evaluate the potentials of microorganisms isolated to utilize spent oil. Three mechanic workshops within Calabar South axis of Cross River State Nigeria were selected and three soil samples were collected from each site. The total heterotrophic bacteria were enumerated on nutrient agar and the hydrocarbon utilizing bacteria on minimal salt medium using the vapor phase method after employing the ten-fold dilutions from 1:10 to 1:100000. The total heterotrophic mean count ranged from 1.28×104 to 3.58×104 cfu/g while mean count of hydrocarbon utilizing bacteria varied from 1.94×104 to 7.34×104 cfu/g. Physicochemical parameters of samples were determined. Such parameters included pH, electrical conductivity and compounds such as nitrate, nitrite, phosphate, calcium, magnesium and potassium. The bacterial isolates evaluated belonged to the genera of Bacillus, Klebsiella, Proteus, Pseudomonas, Enterococcus, Flavobacterium and Micrococcus spp. Klebsiella spp. emerged as the most prevalent heterotrophic bacteria with 29.41% while Bacillus spp, and Enterococcus spp. were the least prevalent with 11.77%. Among the hydrocarbon utilizing bacteria, Pseudomonas flourescens was the most prevalent species with 53.85% while Micrococcus spp. was the least with 15.39%. Amongst the 3 different sites studied, the mechanic workshop at Goldie Street had the highest mean value for both heterotrophic and hydrocarbon utilizing bacteria ranging from 2.52x104 to 3.58 x104 cfu/g for total heterotrophs and 3.27x104 to 7.34x104 cfu/g for hydrocarbon utilizers. The findings reveal that there is a high prevalence of certain populations of active indigenous hydrocarbon oxidizing bacteria which can be monitored and enhanced to bring about bioremediation in the study area.