Growth and phylogenetic properties of novel bacteria belonging to the epsilon subdivision of the Proteobacteria enriched from Alvinella pompejana anddeep-sea hydrothermal vents

Recent molecular characterizations of microbial communities from deep-sea h ydrothermal sites indicate the predominance of bacteria belonging to the ep silon subdivision of Proteobacteria (epsilon Proteobacteria). here, we repo rt the first enrichments and characterizations of four epsilon Proteobacter ia that are directly associated with Alvinella pompejana, a deep sea hydrot hermal vent polychete, or with hydrothermal vent chimney samples. These nov el bacteria were moderately thermophilic sulfur-reducing heterotrophs growi ng on formate as the energy and carbon source. In addition, two of them (Am -H and Ex-18.2) could grow on sulfur lithoautrotrophically using hydrogen a s the electron donor. Optimal growth temperatures of the bacteria ranged fr om 41 to 45 degreesC. Phylogenetic analysis of the small-subunit ribosomal gene of the two heterotrophic bacteria demonstrated 95% similarity to Sulfu rospirillum arcachonense, an epsilon Proteobacteria isolated from an oxidiz ed marine surface sediment. The autotrophic bacteria grouped within a deepl y branching clade of the epsilon Proteobacteria, to date composed only of u ncultured bacteria detected in a sample from a hydrothermal vent along the mid-Atlantic ridge. A molecular survey of various hydrothermal vent environ ments demonstrated the presence of two of these bacteria (Am-N and Am-H) in more than one geographic location and habitat. These results suggest that certain epsilon Proteobacteria likely fill important niches in the environm ental habitats of deep-sea hydrothermal vents, where they contribute to ove rall carbon and sulfur cycling at moderate thermophilic temperatures.