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

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.