Bacteria from spent engine-oil-contaminated soils possess dual tolerance to hydrocarbon and heavy metals, and degrade spent oil in the presence of copper, lead, zinc and combinations thereof

Abstract

We studied the behaviour of 12 metal-resistant bacteria isolated from spent engine oil (SEO)-contaminated soil in Ibadan, Nigeria, during their growth on SEO in mineral salts medium amended singly or in combination with varying concentrations of Cu, Zn and Pb. Kocuria varians PbB3, Kocuria varians MB2 and Achromobacter xylosoxidans CuE2 showed no appreciable growth on SEO even in the absence of metals. Achromobacter xylosoxidans MC1, Achromobacter xylosoxidans CuC3 and Arthrobacter sp. ZnC1 were inhibited by the tested metals in a dose-dependent manner. However, while Acinetobacter sp. ZnB2 and Acinetobacter sp. ZnE3 were similarly inhibited, both degraded appreciable quantities of SEO in the presence of toxic concentrations of Zn2+. Cu2+ at 100 μg mL−1 has no significant effect on the growth of Acinetobacter calcoaceticus CuD2, which degraded 34.7 % and 33.0 % spent oil, respectively, at 0 and 100 μg mL−1 Cu2+. SEO degradation by Pseudomonas sp. PbC4 and Burkholderia cepacia MD1 reduced by 34.8 % and 19.8 %, respectively, at the lowest concentration of Pb2+ (200 μg mL−1) and metal combination (25 μg mL−1) tested. While the activity of strain PbC4 was inhibited at 600 μg mL−1 Pb2+, there was no significant difference (P < 0.05) in the quantity of SEO degraded by isolate MD1 at all concentrations of the combined metals tested. Our results revealed these bacterial strains to be potential candidates for bioremediation of sites co-contaminated with metals and hydrocarbons and, more importantly, provided evidence that some patterns of metal inhibition previously attributed to community effects may also be linked to the physiology of individual degrading bacterial strains.