Regulatory Standard and Research Department, Secretariat of Nuclear Regulation Authority (S/NRA/R), 1-9-9, Roppongi, Minato-Ku, Tokyo, 106-8450, Japan.
Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-Ku, Tokyo, Japan.
Microb Ecol. 2024 Oct 22;87(1):132. doi: 10.1007/s00248-024-02451-7.
Deep underground galleries are used to access the deep biosphere in addition to mining and other engineering applications, such as geological disposal of radioactive waste. Fracture networks developed in the excavation damaged zone (EDZ) are concerned with accelerating mass transport, where microbial colonization might be possible due to the availability of space and nutrients. In this study, microbial biofilms at EDZ fractures were investigated by drilling from a 350-m-deep gallery and subsequent borehole logging at the Horonobe Underground Research Laboratory (URL). By using microscopic and spectroscopic techniques, the dense colonization of microbial cells was demonstrated at the surfaces of the EDZ fractures with high hydraulic conductivity. 16S rRNA gene sequence analysis revealed the dominance of gammaproteobacterial lineages, the cultivated members of which are aerobic methanotrophs. The near-complete genomes from Horonobe groundwater, affiliated with the methanotrophic lineages, were fully equipped with genes involved in aerobic methanotrophy. Although the mediation of aerobic methanotrophy remains to be demonstrated, microbial O production was supported by the presence of genes in the near-complete genomes, such as catalase and superoxide dismutase that produce O from reactive oxygen species and a nitric oxide reductase gene with the substitutions of amino acids in motifs. It is concluded that the EDZ fractures provide energetically favorable subsurface habitats for microorganisms.
除了采矿和其他工程应用（如放射性废物的地质处置）外，地下深处的洞穴还被用于进入深层生物圈。在开采破坏区（EDZ）中发育的裂缝网络与加速物质传输有关，由于空间和养分的可用性，微生物可能会在那里定殖。在这项研究中，通过从 350 米深的隧道中钻探，并在幌延地下研究实验室（URL）进行随后的钻孔测井，研究了 EDZ 裂缝中的微生物生物膜。通过使用显微镜和光谱技术，在具有高水力传导率的 EDZ 裂缝表面上证明了微生物细胞的密集定殖。16S rRNA 基因序列分析显示，在有氧甲烷氧化菌占优势的γ变形菌门的培养成员中，有氧甲烷氧化菌的优势明显。与甲烷氧化菌相关的从幌延地下水中获得的近完整基因组，完全具备参与有氧甲烷氧化的基因。尽管有氧甲烷氧化的介导作用仍有待证明，但近完整基因组中存在的基因支持了微生物 O 的产生，例如过氧化氢酶和超氧化物歧化酶，它们可以从活性氧中产生 O，以及具有氨基酸替换的一氧化氮还原酶基因。结论是，EDZ 裂缝为微生物提供了能量有利的地下栖息地。
