Microbially mediated cobalt cycling? Cobalt resistance and uptake in comamonas testosteroni, isolated from the Zambian copperbelt

Cobalt (Co) cycling in aquatic sediment is known to be coupled to manganese cycling with manganese reducers also responsible for the Co cycling. No study has documented active cobalt uptake in large concentrations by any known microbes. To identify any possible microbes showing active Co uptake, samples were collected from a wetland created from the seepage through a tailings dam located in the Zambian copperbelt. The microbial community from the sediments was selectively enriched for cobalt resistant microorganisms. A dominant aerobic isolate was identified by 16S rRNA gene sequence analysis as Comamonas testosteroni and was designated C. testosteroni TDKW. C. testosteroni TDKW was found to have improved growth with the addition of up to 500 µM of cobalt, with optimal growth occurring at ca. 80 µM. Cobalt concentrations above 4mM completely inhibited growth. C. testosteroni TDKW was resistant to high concentrations of iron and manganese, with growth up to 4mM and 6mM, respectively. The isolate showed little resistance to copper or nickel. Elemental analysis of C. testosteroni TDKW cells cultivated in 100µM cobalt medium showed evidence of intracellular cobalt accumulation. We propose that this organism may play a role in the in vivo biological cycling of cobalt in these contaminated aquatic systems. This novel microbe could have applications in cobalt bioremediation.