地下熱水系における微生物地球化学 : 菱刈金山地下熱水系の研究例(<特集>有機物・微生物・生態系の地球化学)
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This paper reviews biogeochemistry of subsurface geothermal water stream in the Hishikari gold mine, Japan. The stream, which is derived from a subsurface anaerobic aquifer containing plentiful CO_2, CH_4, H_2, and NH_4^+, emerges in a mine tunnel 320 m below the ground level, providing nutrients for a lush microbial community that extends to a distance of approximately 7 m in the absence of sunlight-irradiation. Based on the analysis of 16S rRNA genes amplified from environmental DNA, change of microbial community along the stream was detected. In the hot upper stream (69°C), the dominant bacterial phylotypes were methane-oxidizing γ-Proteobacteria, and hydrogen- and sulfur-oxidizing Sulfurihydrogenibium sp. In contrast, the dominant bacterial phylotypes in the middle and lower stream (62 and 55°C) were closely related to ammonia-oxidizing Nitrosomonas and nitrite-oxidizing Nitrospira spp. Changes in the microbial metabolic potential estimated by quantitative PCR analysis of functional genes encoding the particulate methane monooxygenase (pmoA), ammonia monooxygenase (amoA), and putative nitrite oxidoreductase (nxrB), supported the community shift suggested by the 16S rRNA gene analysis. Decreasing CH_4, H_2 and NH_4^+ contents and increasing NO_2^- and NO_3^- contents in the mat-interstitial water along the stream were consistent with the observed transition of the bacterial community structure in the stream.
- 2010-12-25