" Candidatus Hydrogenisulfobacillus filiaventi" strain R50 gen. nov. sp. nov., a highly efficient producer of extracellular organic compounds from H 2 and CO 2 .

Production of organic molecules is largely depending on fossil fuels. A sustainable alternative would be the synthesis of these compounds from CO ₂ and a cheap energy source, such as H ₂ , CH ₄ , NH ₃ , CO, sulfur compounds or iron(II). Volcanic and geothermal areas are rich in CO ₂ and reduced inorganic gasses and therefore habitats where novel chemolithoautotrophic microorganisms for the synthesis of organic compounds could be discovered. Here we describe " Candidatus Hydrogenisulfobacillus filiaventi" R50 gen. nov., sp. nov., a thermoacidophilic, autotrophic H ₂ -oxidizing microorganism, that fixed CO ₂ and excreted no less than 0.54 mol organic carbon per mole fixed CO ₂ . Extensive metabolomics and NMR analyses revealed that Val, Ala and Ile are the most dominant form of excreted organic carbon while the aromatic amino acids Tyr and Phe, and Glu and Lys were present at much lower concentrations. In addition to these proteinogenic amino acids, the excreted carbon consisted of homoserine lactone, homoserine and an unidentified amino acid. The biological role of the excretion remains uncertain. In the laboratory, we noticed the production under high growth rates (0.034 h ^-1 , doubling time of 20 h) in combination with O ₂ -limitation, which will most likely not occur in the natural habitat of this strain. Nevertheless, this large production of extracellular organic molecules from CO ₂ may open possibilities to use chemolithoautotrophic microorganisms for the sustainable production of important biomolecules.
Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
(Copyright © 2023 Hogendoorn, Pol, de Graaf, White, Mesman, van Galen, van Alen, Cremers, Jansen, Jetten and Op den Camp.)