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P-162:
Identifying methanogenic microbial community members obtained from 2-km deep subseafloor coalbed
○田角 栄二, Tzu-Hsuan Tu, Akira Ijiri, Yuki Morono, Shun'ichi Ishii, Ken Takai, Fumio Inagaki, Hiroyuki Imachi Japan Agency for Marine Science and Technology (JAMSTEC)
During the Integrated Ocean Drilling Program (IODP) Expedition 337, we successfully enriched a methanogenic microbial community from 2 km-deep lignite coalbed samples using a down-flow hanging sponge (DHS) reactor. During the DHS reactor operation for 932 days at near the in-situ temperature of 40°C, we observed a continuous methane production since the 7th day, even without adding any organic substrates in the seawater-based medium after 721 days. The carbon isotopic composition of methane gradually decreased with the operational time from -42.9‰ to -94.0‰, suggesting the significant contribution of microbial methanogenesis. Interestingly, the effluent contained acetate (up to 0.6 mM), which is most likely a major end-product of the heterotrophic microbial activity. Electron microscopic observation of the lignite particles showed that remarkably abundant and morphologically diverse microbial cells tightly attached to the particles. 16S rRNA gene-tag sequence analysis revealed that archaeal community was consisted mainly of a hydrogenotrophic CO2-reducing methanogen related to Methanobacterium. Bacterial community was predominated by the members within Actinobacteria, Bacteroidetes, Firmicutes, Chloroflexi and Gammaproteobacteria. Using the reactor enrichment as inoculum, subsequent batch-type cultivation led to the successful isolation of several anaerobic microorganisms, including the hydrogenotrophic methanogen. These data suggest that the enriched microbial community represents a heterotrophic microbial ecosystem that largely relies on coaly organic matter, and its activity produces both acetate and methane via the degradation of lignite.
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