A novel moderately thermophilic, microaerobic to anaerobic, chemolithoautotrophic bacterium, designated strain CRT, was isolated from a deep-sea hydrothermal vent site at 36degreesN on the Mid-Atlantic Ridge. Cells were Gram-negative, non-motile rods. The organism grew at 45-65 degreesC and pH 6.5-7.4,with optimum growth at 55 degreesC and pH 6.9-7.1. The NaCl range for growth was 5-50 g l(-1) (optimum 30 g l(-1)). Strain CRT was an obligate chemolithoautotroph, growing with H-2 as energy source, sulfur, nitrate or oxygen as electron acceptors and CO2 as carbon source. Hydrogen sulfide and ammonium were the respective products of sulfur and nitrate reduction. The G+C; content of the genomic DNA was 32.1 mol%. Based on 16S rRNA gene sequence analysis, this organism was most closely related to Caminibacter hydrogeniphilus (94.9% similarity). On the basis of phenotypic and phylogenetic data, it is proposed that the isolate represents a novel species, Caminibacter profundus sp. nov. The type strain is CRT (= DSM 15016(T)= JCM 11957(T)). The phylogenetic data also correlate well with the significant phenotypic differences between the lineage encompassing the genera Nautilia and Caminibacter and other members of the class `Epsilonproteobacteria'. The lineage encompassing the genera Nautilia and Caminibacter is therefore proposed as a new order, Nautiliales ord. nov., represented by a single family, Nautiliaceae fam. nov.