Thermovibrio ammonificans sp. nov., a thermophilic, chemolithotrophic, nitrate-ammonifying bacterium from deep-sea hydrothermal vents

1 Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, NJ 08901, USA 2 Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ 08901, USA 3 Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, NJ 08854, USA Correspondence Costantino Vetriani vetriani{at}imcs.rutgers.edu A thermophilic, anaerobic, chemolithoautotrophic bacterium was isolated from the walls of an active deep-sea hydrothermal vent chimney on the East Pacific Rise at 9° 50' N. Cells of the organism were Gram-negative, motile rods that were about 1·0 µm in length and 0·6 µm in width. Growth occurred between 60 and 80 °C (optimum at 75 °C), 0·5 and 4·5 % (w/v) NaCl (optimum at 2 %) and pH 5 and 7 (optimum at 5·5). Generation time under optimal conditions was 1·57 h. Growth occurred under chemolithoautotrophic conditions in the presence of H 2 and CO 2 , with nitrate or sulfur as the electron acceptor and with concomitant formation of ammonium or hydrogen sulfide, respectively. Thiosulfate, sulfite and oxygen were not used as electron acceptors. Acetate, formate, lactate and yeast extract inhibited growth. No chemoorganoheterotrophic growth was observed on peptone, tryptone or Casamino acids. The genomic DNA G+C content was 54·6 mol%. Phylogenetic analyses of the 16S rRNA gene sequence indicated that the organism was a member of the domain Bacteria and formed a deep branch within the phylum Aquificae , with Thermovibrio ruber as its closest relative (94·4 % sequence similarity). On the basis of phylogenetic, physiological and genetic considerations, it is proposed that the organism represents a novel species within the newly described genus Thermovibrio . The type strain is Thermovibrio ammonificans HB-1 T (=DSM 15698 T =JCM 12110 T ). Published online ahead of print on 18 July 2003 as DOI 10.1099/ijs.0.02781-0. The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain HB-1 T is AY263403 . Graphs showing the growth of strain HB-1 T under different conditions are available as supplementary material in IJSEM Online.