5:15 PM - 7:15 PM
[U12-P11] Electrosynthesis by sulfur-oxidizing bacteria from deep-sea hydrothermal fields
Keywords:Origin of Life, Electrochemistry, Electrosynthesis
The “electrochemical evolution theory”, in which electricity generated from deep-sea hydrothermal field droved the prebiotic anabolic metabolisms on the early Earth, has been proposed. If primitive metabolisms were driven by electricity from deep-sea hydrothermal fields, the electrical energy would have continued to be an effective energy source for microbial cells in the subsequent biological evolution. We have suggested the existence of electrosynthetic microorganisms utilizing electrical discharges from modern deep-sea hydrothermal vents. In this study, we report that a sulfur-oxidizing bacterium derived from a deep-sea hydrothermal field has the ability of electrosynthesis.
Electrochemical cultivation was performed in the H-shaped electrochemical reactor simulating the discharge of deep-sea hydrothermal vent, with electricity and carbon dioxide as the sole energy source and the sole carbon source, respectively. Strain SREC-4 belonging to the genus Thiomicrorhabdus, known as a marine sulfur-oxidizer, was dominant after the cultivation. Quantitative PCR analysis showed cell proliferation of the SREC-4. Electrochemical cultivation with 13C-labeled carbon dioxide was performed, and incorporation of 13C was detected at the whole-cells collected from the culture medium including multiple bacteria. Individual cell level analysis combining Nano-SIMS and FISH showed 13C incorporation into the cells particularly of the genus Thiomicrorhabdus. These results strongly suggest that the SREC-4 has the ability of electrosynthetic growth. In addition, gene clusters encoding the extracellular electron uptake pathway and the carbon fixation pathway were found in the genome of the SREC-4, genetically supporting the electrosynthesis by the strain. Genome phylogenetic analysis showed that Thiomicrorhabdus bacteria derived from hydrothermal fields constituted a clade in the phylogenetic tree of the genus, and that extracellular electron uptake pathway gene clusters were found only within the clade. The hydrothermal fields where these genomes derived distributed throughout the various oceans such as the North and South Pacific, Atlantic and Indian Oceans. These results suggest that electrosynthetic Thiomicrorhabdus bacteria inhabit hydrothermal fields around the world.
This work strongly suggests that sulfur-oxidizing bacteria that use electricity as an energy source for growth exist in deep-sea hydrothermal fields around the modern world. In future, mechanism analysis and genetic characteristics of the extracellular electron uptake will help understand the evolutionary process of microbial electricity utilization.
Electrochemical cultivation was performed in the H-shaped electrochemical reactor simulating the discharge of deep-sea hydrothermal vent, with electricity and carbon dioxide as the sole energy source and the sole carbon source, respectively. Strain SREC-4 belonging to the genus Thiomicrorhabdus, known as a marine sulfur-oxidizer, was dominant after the cultivation. Quantitative PCR analysis showed cell proliferation of the SREC-4. Electrochemical cultivation with 13C-labeled carbon dioxide was performed, and incorporation of 13C was detected at the whole-cells collected from the culture medium including multiple bacteria. Individual cell level analysis combining Nano-SIMS and FISH showed 13C incorporation into the cells particularly of the genus Thiomicrorhabdus. These results strongly suggest that the SREC-4 has the ability of electrosynthetic growth. In addition, gene clusters encoding the extracellular electron uptake pathway and the carbon fixation pathway were found in the genome of the SREC-4, genetically supporting the electrosynthesis by the strain. Genome phylogenetic analysis showed that Thiomicrorhabdus bacteria derived from hydrothermal fields constituted a clade in the phylogenetic tree of the genus, and that extracellular electron uptake pathway gene clusters were found only within the clade. The hydrothermal fields where these genomes derived distributed throughout the various oceans such as the North and South Pacific, Atlantic and Indian Oceans. These results suggest that electrosynthetic Thiomicrorhabdus bacteria inhabit hydrothermal fields around the world.
This work strongly suggests that sulfur-oxidizing bacteria that use electricity as an energy source for growth exist in deep-sea hydrothermal fields around the modern world. In future, mechanism analysis and genetic characteristics of the extracellular electron uptake will help understand the evolutionary process of microbial electricity utilization.