Schumann, P.

Despite differences in their morphologies, comparative analyses of 16S rRNA gene sequences revealed high levels of similarity (>94 %) between strains of the filamentous bacterium ‘Candidatus Nostocoida limicola’ and the cocci Tetrasphaera australiensis and Tetrasphaera japonica and the rod Tetrasphaera elongata, all isolated from activated sludge. These sequence data and their chemotaxonomic characters, including cell wall, menaquinone and lipid compositions and fingerprints of their 16S–23S rRNA intergenic regions, support the proposition that these isolates should be combined into a single genus containing six species, in the family Intrasporangiaceae in the Actinobacteria. This suggestion receives additional support from DNA–DNA hybridization data and when partial sequences of the rpoC1 gene are compared between these strains. Even though few phenotypic characterization data were obtained for these slowly growing isolates, it is proposed, on the basis of the extensive chemotaxonomic and molecular evidence presented here, that ‘Candidatus N. limicola’ strains Ben 17, Ben 18, Ben 67, Ben 68 and Ben 74 all be placed into the species Tetrasphaera jenkinsii sp. nov. (type strain Ben 74T=DSM 17519T=NCIMB 14128T), ‘Candidatus N. limicola’ strain Ben 70 into Tetrasphaera vanveenii sp. nov. (type strain Ben 70T=DSM 17518T=NCIMB 14127T) and ‘Candidatus N. limicola’ strains Ver 1 and Ver 2 into Tetrasphaera veronensis sp. nov. (type strain Ver 1T=DSM 17520T=NCIMB 14129T).

A thermophilic, marine, anaerobic, chemolithoautotrophic, sulfate-reducing bacterium, strain CIR29812T, was isolated from a deep-sea hydrothermal vent site at the Kairei vent field on the Central Indian Ridge. Cells were Gram-negative motile rods that did not form spores. The temperature range for growth was 55–80 °C, with an optimum at 70 °C. The NaCl concentration range for growth was 10–35 g l−1, with an optimum at 25 g l−1. The pH range for growth was 6–6·7, with an optimum at approximately pH 6·25. H2and CO2were the only electron donor and carbon source found to support growth of the strain. However, several organic compounds were stimulatory for growth. Sulfate was used as electron acceptor, whereas elemental sulfur, thiosulfate, sulfite, cystine, nitrate and fumarate were not. No fermentative growth was observed with malate, pyruvate or lactate. The phenotypic characteristics of strain CIR29812Twere similar to those ofThermodesulfobacterium hydrogeniphilum, a recently described thermophilic, chemolithoautotrophic sulfate-reducer. However, phylogenetic analyses of the 16S rRNA gene sequences showed that the new isolate was distantly related to members of the familyThermodesulfobacteriaceae(similarity values of less than 90 %). The chemotaxonomic data (fatty acids and polar lipids composition) also indicated that strain CIR29812Tcould be distinguished fromThermodesulfobacterium commune, the type species of the type genus of the familyThermodesulfobacteriaceae. Finally, the G+C content of the genomic DNA of strain CIR29812T(46·0 mol%) was not in the range of values obtained for members of this family. On the basis of phenotypic, chemotaxonomic and genomic features, it is proposed that strain CIR29812Trepresents a novel species of a new genus,Thermodesulfatator, of whichThermodesulfatator indicusis the type species. The type strain is CIR29812T(=DSM 15286T=JCM 11887T).