Identification of novel bacteria capable of accumulating 137Cs under K+ from anaerobic digested sludge for decontamination of 137Cs-contaminated biomass

Abstract

Environmental purification using microorganisms has drawn attention for the decontamination of 137Cs released during a nuclear accident; however, Cs absorption by microorganisms is inhibited by the coexistence of potassium. In this study, we aimed to identify Cs-absorbing bacteria resistant to the inhibition of Cs absorption in the coexistence of potassium for the purpose of decontaminating 137Cs-contaminated biomass. When anaerobic sludge was cultured with the addition of CsCl, Cs accumulated in the microorganisms. This may be because Cs administration promoted the growth of specific Cs-absorbing bacteria. Metagenomics analysis of flora showed that the Tepidibacter genus dominated in the presence of Cs. In addition, Tepidibacter mesophilus accumulated 61.8 kBq/g dry weight of 137Cs in the presence of 4 mM K+, and presented high 137Cs-absorption ability, even in the presence of K+. Moreover, 74% of 137Cs absorption by anaerobic sludge was estimated to be due to bacteria of the Tepidibacter genus. It is assumed that 137Cs in the surface soil layer can be absorbed by surrounding microorganisms along with microbial decomposition of biomass containing a large amount of K+. Therefore, anaerobic sludge containing Tepidibacter genus may be used in the decontamination process of Cs released into environment as a useful Cs-accumulating flora.