Microbial reduction of (Co(III)-EDTA) − by Bacillus licheniformis SPB-2 strain isolated from a solar salt pan

Abstract Naturally stressed habitats are known to be repositories for novel microorganisms with potential bioremediation applications. In this study, we isolated a [Co(III)–EDTA] − reducing bacterium Bacillus licheniformis SPB-2 from a solar salt pan that is exposed to constant cycles of hydration and desiccation in nature. [Co(III)–EDTA] − generated during nuclear waste management process is difficult to remove from the waste due to its high stability and solubility. It is reduced form i.e. [Co(II)–EDTA] 2− is less stable though it is toxic. This study showed that B. licheniformis SPB-2 reduced 1 mM [Co(III)–EDTA] − in 14 days when grown in a batch mode. However, subsequent cycles showed an increase in the reduction activity, which was observed up to four cycles. Interestingly, the present study also showed that [Co(III)–EDTA] − acted as an inducer for B. licheniformis SPB-2 spore germination. Vegetative cells germinated from the spores were found to be involved in [Co(III)–EDTA] − reduction. More detailed investigations showed that after [Co(III)–EDTA] − reduction, i.e. [Co(II)–EDTA] 2− complex was removed by B. licheniformis SPB-2 from the bulk liquid by adsorption phenomenon. The bacterium showed a D 10 value (radiation dose required to kill 90% cells) of ∼250 Gray (Gy), which signifies the potential use of B. licheniformis SPB-2 for bioremediation of moderately active nuclear waste.