海底熱水系の有機物からみた地下生命圏分布 : 水曜海山におけるアミノ酸と酵素活性の特徴(地質, <特集>海底熱水系における生物・地質の相互作用)  [in Japanese] Characterization of Biogenic Amino Acids and Enzymatic Activities in Deep-sea Hydrothermal Systems at Suiyo Seamount, Izu-Bonin Arc, Pacific Ocean(Geology)  [in Japanese]

海底設置型掘削装置を用いて, マグマからの発散物に支えられた島弧型海底火山カルデラ(水曜海山)の掘削調査を行なった。全有機炭素(TOC), 全有機窒素(TON)の分析から海底下にある有機物の鉛直分布を研究し, 全加水分解アミノ酸(THAA)と光学異性体比(D/L比)からサブベント(熱水噴出孔下)を支配する有機物の起源を考察した。アミノ酸のモル分率(mol%)とD/L比の傾向から, サブベントのアミノ酸は, 生物起源であることが判明した。TOCとTHAAは, 正の相関にあり, 有機炭素の濃集部分には, アミノ酸も濃集していることが明らかになった。表層の微生物活動と独立した地下生命圏を検証するため, 同試料について熱的に安定な酵素であるホスファターゼの酵素活性を解析したところ, 有意な活性値を得た。試料の酵素活性値である酸性ホスファターゼ酵素とアルカリホスファターゼ酵素の活性値の鉛直分布は, よく類似しており, 地下生物圏の存在を示す証拠とみなせる。

Deep-sea hydrothermal systems are natural laboratories for the study of organic geochemistry and microbial habitats in extreme environments. A high-temperature deep-sea hydrothermal system related to dacitic arc-volcanism was drilled using a tethered, submarine rock-drill system as part of the Archaean Park Project. The benthic multi-coring system (BMS) employed allowed for direct sampling of microorganisms, rocks and fluids beneath hydrothermal vents. Based on the vertical distribution of organic compounds derived from this vigorous sub-vent environment, a description of deep-sea subterranean chemistry and biology was determined detailing optimal microbial activities. Deep-sea hydrothermal sub-vent core samples of dacitic arc-volcanism obtained at the Suiyo Seamount, Izu-Bonin Arc, in the Western Pacific Ocean were analyzed for total organic carbon (TOC), total organic nitrogen (TON), hydrolyzed amino acids including their D/L ratios, and enzymatic activities such as alkaline and acid phosphatases. Amino acid distributions and their D/L ratios indicated that sub-vent organic matter was influenced by biogenic activity rather than by abiotic chemical synthesis. Useful biomarkers of acid phosphatase (ACP) and alkaline phosphatase (ALP) enzymatic activities were positively correlated with each other and were greatest at the partial middle core sequences; ACP and ALP activities were determined to be as high as 5.1 nmol min^<-1> g-rock^<-1> and 6.8 nmol min^<-1> g-rock^<-1>, respectively. Biochemical indicators of ACP and ALP were consistent with the origin of total hydrolyzed amino acids (THAA) and the chiral ratio of D- and L-amino acid forms. The significant enzymatic activities demonstrated in this study provide crucial evidence that sub-vent regions represent an extreme-environment biosphere, extending the known subterranean habitable spaces of, for example, extremophilic microbes.