Quantifying genome-specific carbon fixation in a 750-meter deep subsurface hydrothermal microbial community

Ömer K. Coskun, Gonzalo V. Gomez-Saez, Murat Beren, Özcan Doğacan, Suna D. Günay, Viktor Elkin, Hakan Hoşgörmez, Florian Einsiedl, Wolfgang Eisenreich, William D. Orsi

Research output: Contribution to journalArticlepeer-review


Dissolved inorganic carbon has been hypothesized to stimulate microbial chemoautotrophic activity as a biological sink in the carbon cycle of deep subsurface environments. Here, we tested this hypothesis using quantitative DNA stable isotope probing of metagenome-assembled genomes (MAGs) at multiple 13C-labeled bicarbonate concentrations in hydrothermal fluids from a 750-m deep subsurface aquifer in the Biga Peninsula (Turkey). The diversity of microbial populations assimilating 13C-labeled bicarbonate was significantly different at higher bicarbonate concentrations, and could be linked to four separate carbon-fixation pathways encoded within 13C-labeled MAGs. Microbial populations encoding the Calvin–Benson–Bassham cycle had the highest contribution to carbon fixation across all bicarbonate concentrations tested, spanning 1–10 mM. However, out of all the active carbon-fixation pathways detected, MAGs affiliated with the phylum Aquificae encoding the reverse tricarboxylic acid (rTCA) pathway were the only microbial populations that exhibited an increased 13C-bicarbonate assimilation under increasing bicarbonate concentrations. Our study provides the first experimental data supporting predictions that increased bicarbonate concentrations may promote chemoautotrophy via the rTCA cycle and its biological sink for deep subsurface inorganic carbon.

Original languageEnglish
Article numberfiae062
JournalFEMS Microbiology Ecology
Issue number5
StatePublished - 1 May 2024


  • DNA stable isotope probing
  • deep biosphere
  • microbial carbon fixation
  • qSIP


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