Haladaptatus paucihalophilus gen. nov., sp. nov., a halophilic archaeon isolated from a low-salt, sulfide-rich spring

Two novel strains of halophilic archaea, DX253(T) and GY252, were isolated from Zodletone Spring, a low-salt, sulfide- and sulfur-rich spring in south-western Oklahoma, USA. The cells were cocci or coccobacilli and occurred singly or in pairs. The two strains grew in a wide range of salt concentrations (0.8-5.1 M) and required at least 5 mM Mg(2+) for growth. The pH range for growth was 5-7.5 and the temperature range was 25-45 degrees C. In addition to having the capacity to grow at relatively low salt concentrations, cells remained viable in distilled water after prolonged incubation. The two diether phospholipids that are typical of members of the order Halobacteriales, phosphatidylglycerol and phosphatidylglycerol phosphate methyl ester, were present. Phosphatidylglycerol sulfate and two unidentified glycolipids were also detected. Each strain had two distinct 16S rRNA gene sequences that were only 89.5-90.8 % similar to sequences from the most closely related cultured and recognized species within the order Halobacteriales. The DNA G+C content of the type strain was found to be 60.5 mol%. The closest relatives were clones and uncharacterized isolates obtained from coastal salt-marsh sediments with salinities equivalent to that of seawater. The physiological, biochemical and phylogenetic differences between strains DX253(T) and GY252 and other previously described genera of extremely halophilic archaea suggest that these novel strains represent a novel species and genus within the family Halobacteriaceae, for which the name Haladaptatus paucihalophilus gen. nov., sp. nov. is proposed. The type strain is DX253(T) (=JCM 13897(T)=DSM 18195(T)=ATCC BAA-1313(T)=KCTC 4006(T)).