A thermophilic, strictly anaerobic, sulfur-reducing epsilonproteobacterium (strain AmH(T)) isolated from deep-sea hydrothermal vents is described. Cells were motile, Gram-negative rods. Growth was observed at 30-55 degrees C, pH 6.0-9.0 and 2-5 % (w/v) NaCl. Chemolithoautotrophic growth occurred with molecular hydrogen or formate as the electron donor and elemental sulfur as the electron acceptor, producing hydrogen sulfide. Heterotrophic and mixotrophic growth occurred with formate as a source of carbon. The dominant phospholipid fatty acids were C(18 : 1)omega7c (73.26 % of the total), C(16 : 1)omega7c (12.70 %) and C(16 : 0) (12.27 %). The genomic DNA G+C content was 33.5 mol%. Phylogenetic analysis based on 16S rRNA gene sequences placed strain AmH(T) within the family Nautiliaceae of the Epsilonproteobacteria. DNA-DNA hybridization experiments between strain AmH(T) and Nautilia lithotrophica DSM 13520(T) revealed a level of relatedness of 34.6 % between the two strains. Based on physiological and phylogenetic characteristics, strain AmH(T) is considered to represent a novel species of the genus Nautilia, for which the name Nautilia profundicola sp. nov. is proposed. The type strain is AmH(T) (=ATCC BAA-1463(T) =DSM 18972(T)).