[B-CG06] 地球惑星科学　生命圏フロンティアセッション

[BCG06-P05] Did life emerge in a deep-sea metal sulfide chimney? New insights from an archaeal genome and a nanoscale microbe-silicate assemblage

*高宮 日南子¹、向井 広樹²、幸塚 麻里子¹、加藤 真悟⁴、伊藤 元雄³、鈴木 庸平¹ (1.東京大学大学院理学系研究科地球惑星科学専攻、2.産業技術総合研究所、3.海洋研究開発機構　高知コア研究所、4.国立研究開発法人理化学研究所)

キーワード：熱水噴出孔、メタゲノム解析、極限環境生物の生態系、生命の起源、微生物の炭素代謝、岩石生命検出

Deep-sea hydrothermal activities have continued for 3.8 billion years on Earth. After the formation of metal sulfide chimneys from high-temperature fluid, their low-temperature interactions with ambient seawater potentially provide the cold, stable habitat for microbial life. In such a challenging habitat with metal toxicity, 16S rRNA gene sequences formerly affiliated within Deep-Sea Hydrothermal Vent Euryarchaeota Subtype 6 (DHVE6) and recently reclassified as Pacearchaeota are dominantly detected by 16S rRNA gene sequence analysis. However, the distribution and metabolic activities of Pacearchaeota in metal sulfide chimneys are largely unknown. In this study, a metal sulfide chimney collected from a deep-sea hydrothermal field in South Mariana Trough was subjected to genome-resolved metagenomics analysis. It was revealed that a near-complete Pacearchaeota genome has carbon metabolism genes involved in glycolysis and pentose phosphate pathway linked to nucleotide salvage pathway with light-independent CO₂incorporating ribulose bisphosphate carboxylase/oxygenase (RubisCO). By comparative analysis of Pacearchaeota genomes from deep-sea metal sulfide deposits and terrestrial subsurface aquifers, the carbon metabolism was commonly found with genes annotated for Cu detoxification. Based on the NanoSIMS ion imaging analysis, we found an evidence of a dense microbial colonization inside the chimney where the surface of chalcopyrite (CuFeS₂) was overlayered with a silica-bearing material enriched in CN, S and P. Our results explain the geographically and physicochemically diverse distributions of Pacearchaeota indicated by 16S rRNA gene sequence analysis as well as the predominance of Pacearchaeota in the metal sulfide chimney where energy sources from photosynthesis and hydrothermal fluid are limited. The carbon metabolism operated by Pacearchaeota in one of candidate environments for the origin of life could be relevant to that operated by primitive life on early Earth.