[M-IS19] Biogeosciences of cold seeps, mud volcanoes, and hydrothermal vents

[MIS19-01] Electricity generation and electrosynthetic microbial ecosystem synchronized to tidal cycles in a deep-sea hydrothermal field

★Invited Papers

*Masahiro Yamamoto^1,2, Yoshihiro Takaki¹, Runa Kobayashi^1,2, Hiroyuki Kashima¹, Miwako Tsuda¹, Akiko Tanizaki¹, Ryuhei Nakamura³, Ken Takai¹ (1.JAMSTEC, 2.Yokohama-City Univ., 3.RIKEN)

Keywords:Deep-sea hydrothermal vent, Power generation, Electrosynthetic ecosystem

Deep-sea hydrothermal vent spontaneously generates electricity via conductive sulfide minerals with redox electron motive force between hydrothermal fluid and seawater. In this case, hydrogen sulfide in hydrothermal fluid and oxygen in seawater function as the main reducing and oxidizing argents, respectively. We installed a fuel cell system using hydrothermal fluid and seawater as the fuels on a deep-sea hydrothermal vent to record the power output and perform electrochemical microbial cultivation using the electricity generated by the fuel cell. After 12 days installation, we collected the fuel cell and observed voltage and current recorded by a voltmeter and an ammeter. Gradual increase of voltage and current was observed after 4 days from the start, and the voltage was stable at approximately 0.6 V after 8 days. This voltage value corresponded to the difference of the redox potentials between hydrothermal fluid and seawater, indicating that the maximum electron motive force was output. In addition, drops of voltage and current were observed in the half-day cycle linking to the time of high tide. It is reported that tide current velocity slowed down at high tide in this sea area, therefore it is considered that supply shortage of oxygen dissolved in seawater to the cathode surface of the fuel cell caused power output drops. Microbial composition analysis showed that one bacterial species was dominant on the cathode, and the metagenomic analysis indicated that the species possesses the ability of electrosynthesis, which can grow using electricity and carbon dioxide as an energy source and a carbon source, respectively. Actually, this bacterial species, named as ‘Candidatus Thiomicrorhabdus electrophagus’, could grow through the electrochemical cultivation under the electrosynthetic conditions in laboratory. These results strongly indicate that electrosynthetic microbial ecosystems supported by electricity generated from deep-sea hydrothermal vents are formed around the vents. In addition, since the electricity generation is influenced by the oxygen supply rate synchronized with tide cycle, electrosynthetic biomass production resulting from the electron flow from hydrothermal fluid to sulfide rocks, microorganisms, and oxygen is also under the influence of the tide cycle.