Terrestrial mud volcanoes (TMVs), connected to deep-subsurface biosphere, are one of the microbiologically understudied natural objects. In such ecosystems, chemolithoautotrophic microorganisms play a pivotal role in the biogeochemical carbon, nitrogen and sulfur cycling by transforming inorganic compounds contained in the fluids. More than 50 active TMVs are located in the Krasnodar Krai (Russia), on the territory of the Taman peninsula and the Western Caucasus. The microbial diversity of these volcanoes has only recently begun to be studied (Merkel et al., 2021). Previously we have described several species of lithoautotrophic anaerobic bacteria from TMVs belonging to Campylobacterota; Proteobacteria, and “Desulfobacterota” (Frolova et al., 2021, Ratnikova et al., 2020, Slobodkina et al., 2022, Slobodkina et al., 2020). In the current study, we report the isolation of new lithoautotrophic strains pertaining to the genus Sedimenticola of the class Gammaproteobacteria.

The genus Sedimenticola was proposed when describing an anaerobic bacterium capable of growth by decomposition of aromatic compounds coupled to selenate respiration (Knight et al., 2002, Narasingarao and Häggblom, 2006). The isolation of a second species of the genus, Sedimenticola thiotaurini (Flood et al., 2015a) revealed new metabolic properties of the genus, such as capabilities of aerobic respiration, sulfur oxidation and chemolithoautotrophy. The genus Sedimenticola is currently represented by two species with validly published names: Sedimenticola selenatireducens DSM 17993 T and Sedimenticola thiotaurini SIP-G1T (Parte et al., 2020). In addition, two more strains of the type species were characterized: Sedimenticola selenatireducens CUZ and Sedimenticola sp. NSS (Carlström et al., 2015). The habitats of these bacteria are marine ecosystems, including sediments, estuaries, and coastal salt marshes. Besides free-living organisms, bacterial endosymbiont of bivalve mollusk Phacoides pectinatus is also assign to the genus Sedimenticola as “Ca. Sedimenticola endophacoides” (Lim et al., 2019). Sedimenticola spp. were enriched and isolated as organoheterotrophs, and the scarcity of species limits our understanding of their physiology and ecological roles.

In the present study we describe two facultatively anaerobic and lithoautotrophic bacterial strains isolated from TMVs and propose to assign them to a novel species, Sedimenticola hydrogenitrophicus sp.nov. We also propose a new family Sedimenticolaceae to accommodate a monophyletic phylogenomic cluster including the genera Sedimenticola, Thiolapillus, “Candidatus Endoriftia” and “Candidatus Thiodiazotropha”.