[U-11] Biogeochemistry of CO world

[U11-P13] Electrochemical survey in deep-sea hydrothermal fields viewing the quest for primordial or extraterrestrial electro-ecosystems

*Masahiro Yamamoto¹, Yoshifumi Kawada¹, Yoshihiro Takaki¹, Runa Kobayashi^1,2, Kosuke Shimoniida^1,2, Mariko Shitara^1,2, Akiko Tanizaki¹, Hiroyuki Kashima¹, Miho Hirai¹, Yutaro Takaya³, Tatsuo Nozaki^1,4,3, Takafumi Kasaya¹, Ken Takai¹ (1.JAMSTEC, 2.Yokohama City University, 3.The University of Tokyo, 4.Kobe University)

Keywords:electrochemical survey, electrosynthesis, deep-sea hydrothermal field

The “electrochemical evolution theory”, in which electricity generated from deep-sea hydrothermal field drove the prebiotic anabolic metabolisms, has been proposed and the study is progressing to prove the theory. Even after the “origin of life” event based on the electricity, the early “life” could have chosen electricity as the energy source for the activity, growth, and maintenance. In fact, there are electrosynthetic microorganisms that grow using electricity as the energy source even on the modern Earth, raising the next questions. Do electrosynthetic microorganisms habitat in modern deep-sea hydrothermal field? Do electrosynthetic ecosystem supported by electricity from hydrothermal field actually exist? Answering the questions will provide important suggestions for the functions and mechanisms of ecosystem on the early Earth or other planets.
In this presentation, we introduce the exploration of electroactive microbial ecosystems using electrochemical survey in deep-sea hydrothermal fields.
We measured electric fields on seafloor on deep-sea hydrothermal fields, and collected rock samples. Several properties about the rock samples, such as electrical conductivity, constituent minerals, elemental compositions, microbial compositions, were analyzed. Multivariate analysis using the data found that the abundance of several microbial species related to electroactive microorganisms increased on the rock samples with high electric field and high conductivity. In particular, one of the species was suggested to be an electrosynthetic microorganism.
This result suggests that electrosynthetic microbial ecosystem can be formed in addition to chemosynthetic ecosystems in deep-sea hydrothermal fields. Within a deep-sea hydrothermal field, there are both locations where chemosynthesis-favorable and electrosynthesis-favorable, depending on the environmental conditions. It means that not only the habitable zone was expanded, but also the robustness of the system was increased due to the diversity of energy strategy. Considering the existence of electricity is necessary for exploration of environments for the primordial and/or extraterrestrial ecosystems, and electrochemical survey can be a powerful tool.