Abstract

A. Sebiomo*, S. A. Bankole and A. O. Awosanya

Ten bacteria and five fungi capable of utilising lubricating oil as carbon source were isolated from mechanic soil. The growth profiles were determined by monitoring the optical density, total viable counts, dry weights and pH of the culture utilizing lubricating oil as sole carbon and energy source. The total viable counts increased significantly with optical density and dry weights of fungi as the days of incubation progressed until the 14th day (P < 0.001). There was significant decrease in pH (P < 0.001) as fungal cells metabolised lubricating oil, Pseudomonas aeruginosa produced the highest optical density and viable count values of 0.441 and 8.31 to the end of 14th day of incubation among all bacterial isolates used in this study. P. aeruginosa also presented lowest pH value of 6.53 after 14 days of incubation between all bacterial isolates. Bacillus licheniformis and Enterobacter aerogenes recorded the lowest optical density and viable count values of 0.19 and 8.1 of all bacterial isolates after 14th day of incubation, Enterobacter aerogenes had the highest pH value of 6.8. Of all the fungal isolates used in this study Aspergillus niger and Aspergillus terreus recorded the highest dry weight and viable count values of 19.3 and 6.41. Trichoderma sp. had the lowest pH, dry weight and viable count values of 5.1, 17 and 6.3, respectively, Aspergillus flavus had the highest pH of 5.6. Correlation analysis indicated negative correlation between optical density and pH (correlation coefficient = ï?«0.174) and between viable counts and pH (correlation coefficient = ï?«0.159), there was positive correlation between viable counts and optical density (correlation coefficient = 0.735). For the fungal isolates there was negative correlation between dry weights and pH (correlation coefficient = ï?«0.958) and between viable counts and pH (correlation coefficient = -0.830). The correlation analysis between fungal dry weights and viable counts showed positive correlation (0.786). The utilization of hydrocarbon in lubricating oil resulted in gradual reduction in the oil layer and complete disappearance of the oil with prolonged incubation. This study has shown that the microorganisms isolated from mechanic soils have potential application in the bioremediation of sites polluted with lubricating oil.