Natronotalea proteinilytica gen. nov., sp. nov. and Longimonas haloalkaliphila sp. nov., extremely haloalkaliphilic members of the phylum Rhodothermaeota from hypersaline alkaline lakes.

Two proteolytic bacterial strains, BSker2T and BSker3T , were enriched from sediments of hypersaline alkaline lakes in Kulunda Steppe (Altai, Russia) with chicken feathers as substrate, followed by pure culture isolation on hypersaline alkaline media with casein. The cells were non-motile, filamentous, flexible rods. The isolates were obligately aerobic heterotrophs utilizing proteins and peptides as growth substrates. Both were obligate alkaliphiles, but differed in their pH optimum for growth: pH 9.5-9.8 for Bsker2T and pH 8.5-8.8 for BSker3T . The salt range for growth of both isolates was between 2 and 4.5 M total Na+ with an optimum at 2.5-3 M. No organic osmolytes were detected in cells of BSker2T , but they accumulated high intracellular concentrations of K+ . The polar lipid fatty acids were dominated by unsaturated C16 and C18 species. The 16S rRNA gene phylogeny indicated that both strains belong to the recently proposed phylum Rhodothermaeota. BSker2T forms a novel genus-level branch, while BSker3T represents a novel species-level member in the genus Longimonas. On the basis of distinct phenotypic and genotypic properties, strain BSker2T (=JCM 31342T =UNIQEM U1009T ) is proposed to be classified as a representative of a novel genus and species, Natronotalea proteinilyticagen. nov., sp. nov., and strain BSker3T (=JCM 31343T =UNIQEM U1010T ) as a representative of a novel species, Longimonas haloalkaliphila sp. nov.