Hydrostatic pressure helps to cultivate original bacteria from subseafloor rocks of Atlantis Massif, characterization of a novel anaerobe: Petrocella atlantisensis gen. nov. sp. nov.. Genome analysis of Petrocella atlantisensis

Rock-hosted deep subseafloor ecosystems are very challenging for life and current knowledge about microorganisms inhabiting such lithic environments is still limited. This study explored cultivable microbial diversity in various anaerobic enrichment cultures from rock cores recovered during International Ocean Discovery Program (IODP) Expedition 357 from the Atlantis Massif (Mid-Atlantic Ridge, 30°N), which hosts Lost City serpentinite-hosted hydrothermal field. Here, we report the first successful enrichment and isolation of anaerobic bacteria from subseafloor rocks. 16S rRNA-gene analyses showed that Firmicutes and Proteobacteria dominated microbial communities enriched at 10–25°C and marine pH 8.5. Drastic differences in cultivable microbial diversity were observed depending on incubation pressure: atmospheric pressure (0.1 MPa) or hydrostatic pressures mimicking the in-situ conditions (8.2 and 14 MPa). Bacteria belonging to known genera Tessaracoccus, Citrobacter, Proteiniclasticum, Tissierella and Bacillus were isolated at 0.1 MPa, while isolation of a novel anaerobic bacterium was made possible at 14 MPa from core sample M0070C-3R1 (-1150 mbsf). This strain designed 70B-AT is a mesophilic, moderately halotolerant and piezotolerant chemoorganotroph able to use yeast extract, tryptone, glycerol, mannitol, pyruvate and a large range of carbohydrates as carbon sources. Genomic analysis supported a heterotrophy lifestyle. We propose the name ‘Petrocella atlantisensis’ for this novel species of a novel genus within the newly described family ‘Vallitaleaceae’ (order Clostridiales, phylum Firmicutes).