[B-CG07] 岩石生命相互作用とその応用

[BCG07-06] Meta-omic Characterizations of Ultra-Deep Biosphere Hosted in Bushveld Complex

*Castillo Hernadez Julio¹、鈴木 庸平²、小笠原 宏³、矢部 康男⁴ (1.Department of Microbiology and Biochemistry, University of the Free State, South Africa、2.東京大学地球惑星科学専攻、3.立命館大学理工学部、4.東北大学大学院理学研究科)

キーワード：Bushveld complex、Serpentinization、SLiMeEs、ICDP-BCDP、Meta-omic Characterizations

The Bushveld complex is a prime target for deep life studies due to the serpentinization reaction (i.e., the reaction of Fe- and Mg-rich olivine and pyroxene with fracture water) that has the potential for abiotic H₂ production fuelling for subsurface lithoautotrophic microbial ecosystems (SLiMeEs). Due to this, some studies have described the planktonic microbial fraction (cells living in the water fracture) that inhabit the Bushveld fracture water. However, these studies overlooked a significant proportion—potentially up to 80%—of sessile or attached microorganisms residing in the rock, obviously due to the inaccessibility to the heart of the Bushveld complex. Fortunately, the International Continental Scientific Drilling Program (ICDP) Bushveld Complex Drilling Project (BCDP) aims to develop nearly continuous reference sections through the ~8 km-thick Bushveld Complex, offering a unique opportunity to explore its deep biosphere. In this intricate subsurface ecosystem, sessile or attached microorganisms to the rocks are believed to exhibit heightened metabolic activity compared to their planktonic counterparts. The occurrence of microbiofilms in the core fractures might also facilitate diverse microbial interactions, such as intercellular communication via quorum sensing, horizontal gene transfer, viral interactions, competition, cooperation, and resistance to metal toxicity. The chromitite layers of ultramafic rocks in the Bushveld are enriched in toxic metals, also leading to the selection of metal-resistant microorganisms. Thus, established microbial ecosystems might be distinct from those hosted in deep ultramafic rocks poor in heavy metals. Therefore, it is imperative to bioprospect the cores from the deep sections of the Bushveld complex to provide a better resolution of their microbial dark matter, survival mechanism subjected to the serpentinization process and metal toxicity, and evolutive process within an isolated system. The discovery of unknown biological metabolisms (with biotechnological potential) or primordial microorganisms through joint research (Japan and South Africa) under this project would significantly impact the academic world and economic society.