Cultivating microbial communities from the serpentinite-hosted Prony Bay hydrothermal field on different carbon sources in hydrogen-fed bioreactors

With the exception of glycine, the chosen carbon substrates allowed the growth of microbial consortia characterized by significant enrichment of individual taxa. Surprisingly, these taxa were dominated by microbial genera characterized as aerobic rather than anaerobic as expected. Our results indicate the presence of both autotrophic and heterotrophic taxa that may function as foundation species in serpentinite-hosted shallow subsurface ecosystems. We propose that an intricate feedback loop between these autotrophic and heterotrophic foundation species facilitates ecosystem establishment. Bicarbonate-fixing Meiothermus and Hydrogenophaga, as well as formate-fixing Meiothermus, Thioalkalimicrobium, and possibly a novel genotype of Roseibaca might produce organic compounds for heterotrophs at the first trophic level. In addition, the base of the trophic network may include heterotrophic Roseibaca, Acetoanaerobium, and Meiothermus species producing CO₂ from acetate for a more diverse community of autotrophs. The cultivated archaeal community is expected to recycle CH₄ and CO₂ between Methanomicrobiales and Methanosarcinales with putative Woesearchaeales symbionts.