Tianxiuia mixotrophica gen. nov., sp. nov., an anaerobic, facultative mixotrophic, iron(III)-reducing bacterium isolated from the Tianxiu hydrothermal field and the proposal of Fusibacteraceae fam. nov.

An anaerobic, salt-tolerant, rod-shaped bacterium, strain JL216-2T, was isolated from the shell of the hydrothermal gastropod Alviniconcha marisindica in the Tianxiu hydrothermal field on the Carlsberg Ridge, Indian Ocean. Cells of strain JL216-2T were motile and 0.5×3-6 µm in size. Strain JL216-2T grew at 10-32 °C (optimal 28 °C), pH 6.0-9.0 (optimal pH 7.0) and 0.5-12.0% (w/v) sodium chloride(NaCl, optimal 2.5%). Strain JL216-2T exhibited metabolic versatility, being capable of heterotrophic growth on complex organic compounds. It also performed autotrophic growth by utilizing carbon dioxide (CO₂) fixation or sodium bicarbonate (NaHCO3) as the sole carbon source, driven by hydrogen oxidation coupled with Fe(III) reduction. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain was most closely related to Helicovermis profundi S502T (90.43% sequence similarity). The genome size of strain JL216-2T was 4.91 Mb, with a G+C content of 39.54 mol%. Phylogenomic analysis and overall genome relatedness indices values indicated a close relatedness of strain JL216-2T to H. profundi S502T and Fusibacter spp. The combined genotypic and phenotypic data showed that strain JL216-2T represents a novel genus within the order Eubacteriales. The type strain is JL216-2T (=MCCC M30262T=KACC 23553T).