Characterization of two novel haloalkaliphilic archaea Natronorubrum bangense gen. nov., sp. nov. and Natronorubrum tibetense gen. nov., sp. nov.

Two haloalkaliphilic archaea were isolated from a soda lake in Tibet. The two strains, designated A33T and GA33T, were Gram-negative, pleomorphic, flat, non-motile and strictly aerobic. Growth required at least 12% NaCl. Growth was between pH 8.0 and pH 11 with an optimum at pH 9.0-9.5. Cells were chemo-organotrophic. Polar lipids were C20-C25 derivatives of phosphatidylglycerol and phosphatidylglycerol phosphate. The nucleotide sequences of the 16S rRNA genes from the two strains were obtained by the analysis of the cloned rDNAs. On 16S rRNA phylogenetic trees, the two strains formed a monophyletic cluster. They differed from their closet neighbours, Halobacterium trapanicum and Natrialba asiatica, in polar lipid composition, as well as physiological and phenotypic characteristics. DNA-DNA hybridization indicated that the two strains belonged to different species of the same genus. The results indicated that the strains A33T and GA33T should be classified in a new genus Natronorubrum gen. nov. as Natronorubrum bangense sp. nov. (strain A33T) and Natronorubrum tibetense sp. nov. (strain GA33T).