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The continuous and indiscriminate discharge of crude and/or refined oils during the various processing and transportation of oils leads to the contamination of the environment. This study was aimed at determining the bacterial diversity of contaminated soils around tank farm areas and the changes that occur in the oil hydrocarbon components during the process of biodegradation by the selected bacterial species. Contaminated soil samples were collected around different tank farm areas based on their petroleum contents at the Nigerian National Petroleum Corporation (NNPC) depot, Apata, Ibadan, Oyo State, Nigeria. The total heterotrophic bacterial count ranged from 1.04 × 107 to 2.73 × 107 cfu/ml in the various contaminated soil samples. The hydrocarbon utilizing bacteria count ranged from 1.9 × 103 to 7.3 × 103 cfu/ml in the contaminated soil samples. Among the 28 bacterial isolates capable of utilizing crude oil vapour, two isolates thrived on the highest crude oil concentration employed during screening and were used singly and in a mixed culture for the biodegradation of the contaminated soil samples. The two hydrocarbon-utilizing bacteria isolates were characterized and identified as Pseudomonas species (AG13) and Bacillus species (PM4). The percentage degradation of the aliphatic and aromatic hydrocarbons in the contaminated soil samples after 8 weeks was highest in the Pseudomonas species (AG13) treated sample with 71.51% and 63.30% respectively and this was followed closely by the mixture of both bacteria isolates with 67.14% and 50.69% respectively and Bacillus species (PM4) having the lowest with 31.92% and 19.03% respectively. Therefore, hydrocarbon-utilizing bacteria species can be employed in the removal of oil pollutants from the soil, but a careful selection is required to ensure effectiveness.
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