Screening for Biodegradative Activity of Diesel Oil by Microorganisms Isolated from Petroleum Polluted Soil of a Mechanic Workshop at AKAD Community, Akure, Nigeria

This study was carried out to determine the bacterial and fungal flora of soils contaminated with used automobile engine oil at a mechanic workshop at AKAD community, Akure, Ondo State, Nigeria, with the aim of testing their ability to degrade diesel oil. Isolation and identification of microbes were done using standard microbiological techniques. Oil degrading activity of the isolates were assayed for using Bushnell Haas broth (BHB) supplemented with 1% diesel oil. The growths and activities of the bacterial isolates in the Bushnell-Haas broth (BHB) were monitored for seven days by taking the optical density, pH changes, and free CO2 produced in the broth by the microbes. The bacterial species isolated and identified were Staphylococcus aureus, Micrococcus luteus, Bacillus subtilis, Proteus mirabilis, and Pseudomonas aeruginosa. All of the isolates showed degradative activity with the increase in optical density and free carbon dioxide (CO2) produced in the broth. However, the most effective diesel degrader with respect to free CO2 produced was Proteus mirabilis, while Pseudomonas aeruginosa was most effective with respect to optical density of the broth. The fungal species isolated and identified were Aspergillus terreus, Candida species, and Aspergillus niger. The most effective diesel degrader with respect to free CO2 produced is Aspergillus terreus, while Candida species was most effective with respect to optical density of the broth. Also, the growth of all bacterial and fungal isolates increased with decreasing pH. Overall, the bacterial isolates had higher degrading activities over fungal isolates throughout the incubation period. The results of this investigation revealed that hydrocarbon polluted soils harbour beneficial microorganisms, which can have obvious environmental implications because they carry out activities such as the biodegradation of diesel oil. Thus, further investigations can be carried out to validate their ability to remove hydrocarbon from the polluted environment.