Characterization of a corrosive methanogen isolated from the subsurface environment

Hirano, Shinichi*; Nagaoka, Toru*; Kosaba, Takumi*; Amano, Yuki   ; Mochizuki, Akihito  

The effects of microbial corrosion induced by microorganisms have been reported for rapid corrosion and localized corrosion that occurs in environments that are not susceptible to chemical corrosion. In geological disposal projects where radioactive waste is buried deep underground, it is considered that radioactive waste should be encapsulated in an engineered barrier (overpack (metal disposal container), buffer material) and buried underground to ensure the confinement of the radioactive waste. Since a variety of microorganisms exist in the deep subsurface, it is necessary to consider the corrosive effects of microorganisms on the metal disposal container when evaluating the confinement performance of the engineered barriers. However, there have been limited studies on corrosion by microorganisms in the subsurface. Therefore, the objective of this study was to search for the presence of microorganisms causing iron corrosion in deep groundwater at the Horonobe Underground Research Laboratory and to evaluate their corrosion activity. Microorganisms in the groundwater collected from the Horonobe Underground Research Laboratory were cultured under anaerobic conditions with carbon steel coupons. As a result, methane gas was detected in some of the groundwater culture solutions, and a prefectural weight loss and localized surface thinning of the carbon steel specimens were observed. Analysis of the microbiota in the groundwater after incubation revealed an increase in the proportion of Methanobacterium spp. in the samples with corrosive activity, so further accumulation culture was conducted using iron granules to obtain Methanobacterium isolates. Based on the results of 16S rRNA gene sequence analysis of the isolate, we designated it as Methanobacterium sp. strain H04.