Selective metal accumulation by metal-resistant bacteria growing on spent engine oil in single and ternary metal mixtures

Abstract

Three metal-resistant bacteria species, identified as Pseudomonas alcaligenes B101, Pseudomonas fluorescens C101 and Stenotrophomonas maltophilia E103, isolated from spent engine oil-contaminated tropical soils utilised spent engine oil (SEO) as a source of nutrient for growth in the presence of Pb2+ (500 µg/ml), Cu2+ (400 µg/ml) and Zn2+ (400 µg/ml) with concomitant cellular accumulation of the metals in single and ternary mixtures. Degradation of SEO in the presence of the metals and their mixture within a 21 days experimental period ranged between 27.8 and 57.8% compared to 52.2% and 66.7% in metal free controls with extensive modification (up to 92.7%) of the aromatic fractions of the spent oil. Cellular accumulation of the metals during SEO degradation ranged between 0.13 and 30.76%, and 3.77% and 33.43%, respectively, in growth media supplemented with single metal ions and their mixtures. Stenotrophomonas maltophilia E103 showed the best potential for metal uptake, accumulating the highest concentration of Pb2+ (29.0%) and Zn2+ (30.8%) in systems supplemented with single metals, while P. alcaligenes B101 and P. fluorescens C101 showed preference for the accumulation of Pb2+ (15.1%) and Cu2+ (23.8%), respectively. Although metal uptake decreased significantly in ternary metal systems, strains B101 and E103 maintained their preferences for Pb2+ in the ternary systems. The ability of these bacteria to metabolise spent engine oil with concurrent intracellular metal accumulation in the presence of high concentrations of Pb2+, Cu2+ and Zn2+ and their mixtures highlighted their potentials for use in the remediation of sites exposed to hydrocarbon-metal co-contamination.