Selective Isolation and Phenotypic Characterization of Bacteria and Actinomycetes from Oil-contaminated Soils

Large numbers of bacteria and actinomycete strains were isolated from two contaminated soils with high total petroleum hydrocarbons (TPH) content. From five selective media formulations used, nutrient agar and glucose yeast extract agar showed the best results. Bacterial colony forming units per dry gram soil (ufc/g) ranged from 5.14x10³ to 4.20x10¹¹, whereas for actinomycetes was from 8.99x10⁴ to 9.2x10⁷ ufc/g. Seventy-three bacteria and ninety-three actinomycete isolates were recovered from the two soils. Numerical taxonomy analysis of phenotypic data shows that at 90% similarity, the bacteria could be divided into sixteen multimembered and fifteen single-membered phenetic-groups, while the actinomycetes were separated in twenty multimembered and four single-membered phenetic-groups. Out of the one hundred and sixty-six strains, only ten were unable to use gasoline or oil as sole carbon and nitrogen sources. Most of the isolates could degrade both hydrocarbons. The results of this study show that bacteria and actinomycetes are present in large numbers in high TPH contaminated soils, with an extraordinary degree of diversity and that they can use oil or its derivatives as nutrients.