Abstract

The discharge of used crankcase oil from vehicles is a major source of oil pollution in Buea. The objectives of this study were to isolate and characterize bacteria capable of effectively degrading and cleaning up waste engine oil in this locality and also to ascertain the influence of some environmental factors on the rates of degradation of these isolates. Seventy-two soil samples collected from lubricating oil dump sites (3 auto-mechanic workshops and 3 petrol filling stations, comprising impacted soils) and uncontaminated plots (non-impacted soils) (controls) were analysed for oil-degrading and heterotrophic bacteria following standard microbiological and biochemical methods. The ability of cultures to degrade lubricating oil was also tested individually and in mixed bacterial consortium at different temperatures and nutrient concentrations. Results were analysed using the chi-squared test. P values of < 0.05 were considered significant. Heterotrophic bacterial counts were significantly higher (P< 0.05) in non-impacted than in impacted soils.  Conversely, the population of oil degraders was significantly lower (P < 0.05) in non-impacted than in impacted soils. Oil degraders isolated included Pseudomonas fluorescens, Bacillus mycoides and Serratia marcescens. Of the pure isolates, Serratia marcescensdegraded the highest amount of oil (36.2%).  However, a mixed culture of the isolates proved to be more effective, degrading 38.1% of oil within 20 days.  All the isolates exhibited highest degradation at 32°C; and degradation rates ofPseudomonas fluorescens and Bacillus mycoides increased with increase in nutrient concentration. This study, the first of its kind in Buea, revealed the presence of oil-degrading bacteria in soils as well as the physico-chemical requirements of these bacteria for optimum degradation. This finding could be exploited in case of oil-spill clean-up campaigns.

Key words: environmental pollution, oil-degrading bacteria, heterotrophic bacteria, physico-chemical factors, bioremediation, Cameroon.