The degradation potentials of bacteria and actinomycetes of spent motorcycle lubricating oil were investigated using standard microbiological procedures. Ten composite soil samples were collected from ten different motorcycle mechanic workshops in Benin City. The mean heterotrophic count for bacteria and actinomycetes ranged from 68 x 104 cfu/g to 155 x 104 cfu/g and 43 x 104 cfu/g to 85 x 104 cfu/g respectively. The mean hydrocarbon degrading bacteria counted ranged from 47 x 104 cfu/g to 89 x 104 cfu/g, while that of actinomycetes ranged from 18 x 104 cfu/g to 46 x 104 cfu/g, indicating that the bacteria was greater numerically than the actinomycetes. The preliminary screening test carried out showed that the predominant hydrocarbon degrading bacteria belonged to Micrococcus and Sporosarcina species while that of actinomycetes were Nocardia sp , Gordonia sp , Micromonospora sp and Rhodococcus sp. Biodegradation test conducted revealed a range of 2.5% to 6.6% degradation and 1.035% to 7.53% degradation of the spent lubricating oil in bacteria and actinomycetes respectively, indicating a higher degradation of the spent oil by the actinomycetes.
