Halomicrococcus hydrotolerans gen. nov., sp. nov., an extremely halophilic archaeon isolated from a subterranean salt deposit

A halophilic archaeon, strain H22(T), was isolated from a subterranean salt deposit sampled at Yunnan salt mine, PR China. Colonies of strain H22(T) were light pink-pigmented. Cells were coccus, non-motile, Gram-stain-negative, and did not lyse in distilled water. The strain was aerobic and grew at 20-55 degrees C (optimum, 37 degrees C), in the presence of 10-30% (w/v) NaCl (20%) and at pH 6.5-9.0 (pH 7.0). Mg2+ was required for growth (optimum, 0.005 M). Major polar lipids were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester and sulfated mannosyl-glucosyl-glycerol diether-1. Sequence similarity search based on the multiple 16S rRNA genes (rrnA, rrnB and rrnC) of strain H22(T) revealed that it was most closely related to species of the genera Haloarchaeobius, Haladaptatus, Halorussus and Halorubellus with relative low sequence similarities (91.9-93.7 %). The strain, however, shared highest rpoB' gene sequence identities with Halorussus rarus TBN4(T) (90.8 % rpoB' gene sequence similarity). Phylogenetic trees based on 16S rRNA and rpoB' gene sequences revealed a robust lineage of the strain H22(T) with members of related genera of the family Halobacteriaceae. The DNA G+C content of strain H22(T) was 62.9 mol%. Genome-based analysis of average nucleotide identity (ANI) and in silico DNA-DNA hybridization (DDH) between strains H22(T) and its closest relative were equal or lower than 77.7 and 22.4%, respectively, which were far below the threshold for delineation of a new species. Based on ANI values, in silico DDH, and distinct morphological and physiological differences from the previously described taxa, we suggest that strain H22(T) represents a novel species of a new genus within the family Halobacteriaceae, for which the name Halomicrococcus hydrotolerans gen. nov., sp. nov. is proposed. The type strain is H22(T) (=CGMCC 1.16291(T)=NBRC 113231(T)).