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, BSker2 and BSker3, 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 Bsker2 and pH 8.5-8.8 for BSker3. 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 BSker2, 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. BSker2 forms a novel genus-level branch, while BSker3 represents a novel species-level member in the genus Longimonas. On the basis of distinct phenotypic and genotypic properties, strain BSker2 (=JCM 31342=UNIQEM U1009) is proposed to be classified as a representative of a novel genus and species, Natronotalea proteinilyticagen. nov., sp. nov., and strain BSker3 (=JCM 31343=UNIQEM U1010) as a representative of a novel species, Longimonas haloalkaliphila sp. nov.