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

Abstract

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 c-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 6C and had temperature optima of 30 or 20-35 6C. 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 Halophilic and halotolerant micro-organisms are typically isolated from hypersaline environments such as lagoons, saline and haloalkaline lakes (the Dead Sea, Great Salt Lake, thalassohaline Antarctic lakes, African rift soda lakes), artificial salterns, cured and salty foods, briny petroleum reservoirs, hypersaline desert soils and sea ice (Ventosa et al., 1982(Ventosa et al., , 1998Vreeland et al., 1980;Quesada et al., 1984;Franzmann et al., 1987a;James et al., 1990;Valderrama et al., 1991;Adkins et al., 1993;Duckworth et al., 1996 Duckworth et al., , 2000 Bowman et al., 1997;Satomi et al., 1997; Mormile et al., 1999;Bouchotroch et al., 2001;Yoon et al., 2002;Reddy et al., 2003). They have also recently been found in the very dry environment of the walls and murals of a Details of growth rates of the novel isolates under varying temperatures and salt concentrations, transmission electron micrographs of cells and a 16S rDNA-based maximum-likelihood tree including a wider range of reference species are available as supplementary material in IJSEM Online.

Halomonas alkaliphila sp. nov., a novel halotolerant alkaliphilic bacterium isolated from a salt pool in Campania (Italy)

“…1). In particular, the strain 18bAG T showed the highest similarity (99.0%) with Halomonas venusta DSM 4743 T and Halomonas hydrothermalis DSM 15725 T (Arahal and Ventosa, 2002;Kaye et al, 2004) and the phylogenetic distance from any other validly described species within the genus Halomonas was 97.0%. Halomonas hydrothermalis DSM 15725 T exhibited levels of DNA-DNA relatedness of 56.0% and 41.2%, respectively.…”

“…Halomonas hydrothermalis was not included yet in group 2, because it was isolated in 2004 (Kaye et al, 2004). In this group was also included inter alia the alkaliphilic Halomonas magadiensis.…”

“…ND, not determined. Data were taken from Mata et al (2002); Arahal and Ventosa (2002); James et al (1990), Kaye et al (2004) and present studies. The tree was obtained using the neighbor-joining method.…”

“…Among Halomonas species, most of them grew in a wide pH range and were considered alkalitolerant (Kaye et al, 2004;Quillaguamán et al, 2004;and references therein); examples of species optimally growing at alkaline pH are also reported (Berendes et al, 1996;Duckworth et al, 2000;Heyrman et al, 2002;Mormile et al, 1999;Romano et al, 1996Romano et al, , 2005.…”

“…Halomonas have been isolated in every part of the world and from several sources every year (Arahal and Ventosa, 2002;García et al, 2004;Heyrman et al, 2002;Kaye et al, 2004;Lim et al, 2004;Martínez-Cánovas et al, 2004a, b;Mata et al, 2002;Quillaguamán et al, 2004;and references therein).…”