Halomonas neptunia sp. nov., Halomonas sulfidaeris sp. nov., Halomonas axialensis sp. nov. and Halomonas hydrothermalis sp. nov.: halophilic bacteria isolated from deep-sea hydrothermal-vent environments

1 University of Washington, School of Oceanography, Box 357940, Seattle, WA 98195, USA 2 Departamento de Microbiología y Parasitología, Facultad de Farmacia, Universidad de Sevilla, 41012 Seville, Spain Correspondence Jonathan Z. Kaye jzkaye{at}ocean.washington.edu To assess the physiological and phylogenetic diversity of culturable halophilic bacteria in deep-sea hydrothermal-vent environments, six isolates obtained from low-temperature hydrothermal fluids, sulfide rock and hydrothermal plumes in North and South Pacific Ocean vent fields located at 1530–2580 m depth were fully characterized. Three strains were isolated on media that contained oligotrophic concentrations of organic carbon (0·002 % yeast extract). Sequencing of the 16S rRNA gene indicated that all strains belonged to the genus Halomonas in the -subclass of the Proteobacteria . Consistent with previously described species, the novel strains were slightly to moderately halophilic and grew in media containing up to 22–27 % total salts. The isolates grew at temperatures as low as -1 to 2 °C and had temperature optima of 30 or 20–35 °C. Both the minimum and optimum temperatures for growth were similar to those of Antarctic and sea-ice Halomonas species and lower than typically observed for the genus as a whole. Phenotypic tests revealed that the isolates were physiologically versatile and tended to have more traits in common with each other than with closely related Halomonas species, presumably a reflection of their common deep-sea, hydrothermal-vent habitat of origin. The G+C content of the DNA for all strains was 56·0–57·6 mol%, and DNA–DNA hybridization experiments revealed that four strains (Eplume1 T , Esulfide1 T , Althf1 T and Slthf2 T ) represented novel species and that two strains (Eplume2 and Slthf1) were related to Halomonas meridiana . The proposed new species names are Halomonas neptunia (type strain Eplume1 T =ATCC BAA-805 T =CECT 5815 T =DSM 15720 T ), Halomonas sulfidaeris (type strain Esulfide1 T =ATCC BAA-803 T =CECT 5817 T =DSM 15722 T ), Halomonas axialensis (type strain Althf1 T =ATCC BAA-802 T =CECT 5812 T =DSM 15723 T ) and Halomonas hydrothermalis (type strain Slthf2 T =ATCC BAA-800 T =CECT 5814 T =DSM 15725 T ). Abbreviations: MEF, Main Endeavour Field; SEPR, Southern East Pacific Rise Published online ahead of print on 31 October 2003 as DOI 10.1099/ijs.0.02799-0. The GenBank accession numbers for the 16S rRNA gene sequences of strains Eplume1 T , Eplume2, Esulfide1 T