A novel piezophilic thermophilic anaerobic fermentative bacterial strain, designated strain DY22613T, was isolated from a deep-sea hydrothermal sulfide deposit at the East Pacific Rise (102.6° W, 3.1°S). Cells of strain DY22613T were long motile rods (10 to 20 μm in length, 0.5 μm in width) with peritrichous flagella and stained Gram-negative. Growth was recorded at 44-72 °C (optimum 60-62 °C) and at hydrostatic pressures of 0.1-55 MPa (optimum 20 MPa). The pH range for growth was from 5.0 to 9.0 with an optimum pH at 7.0. Growth was observed from 1 to 8% (w/v) sea salts and 0.65 to 5.2% (w/v) NaCl, with optimum salt concentrations at 3.5% for sea salts and at 2.3% for NaCl. Under optimal growth conditions, the shortest generation time observed was 27 min (60 °C, 20 MPa). Strain DY22613T was heterotrophic, able to utilize complex organic compounds, amino acids, sugars, and organic acids, including peptone, tryptone, beef extract, yeast extract, alanine, glutamine, methionine, phenylalanine, serine, threonine, fructose, fucose, galactose, gentiobiose, glucose, mannose, melibiose, palatinose, rhamnose, turanose, pyruvate, lactic acid, methyl ester, erythritol, galacturonic acid and glucosaminic acid. Strain DY22613T was able to reduce Fe(Ⅲ) compounds, including Fe(Ⅲ) oxyhydroxide (pH 7.0), amorphous iron(Ⅲ) oxide (pH 9.0), goethite (α-FeOOH, pH 12.0), Fe(Ⅲ) citrate and elementary sulfur. Products of fermentation were butyrate, acetate and hydrogen. Main cellular fatty acids were iso-C15:0, 3-OH C14:0 and C14:0. The DNA G+C content of the genomic DNA of strain DY22613T was 36.7 mol%. Based on 16S rRNA gene sequence analysis, the strain forms a novel lineage within the class ‘Clostridia’ and clusters with the order Haloanaerobiales (86.92% 16S rRNA gene sequence similarity). The phylogenetic data suggest that the lineage represents at least a novel genus and species, for which the name Anoxybacter fermentans gen. nov., sp. nov. is proposed. The type strain is DY22613T (=JCM 19466T; =DSM 28033T; =MCCC 1A06456T).