Natrarchaeobius chitinivorans gen. nov., sp. nov., and Natrarchaeobius halalkaliphilus sp. nov., alkaliphilic, chitin-utilizing haloarchaea from hypersaline alkaline lakes.

Two groups of alkaliphilic haloarchaea from hypersaline alkaline lakes in Central Asia, Egypt and North America were enriched and isolated in pure culture using chitin as growth substrate. These cultures, termed AArcht, were divided into two groups: group 1 which includes eleven isolates from highly alkaline soda lakes and group 2 which contains a single isolate obtained from the alkaline hypersaline Searles Lake. The colonies of chitin-utilizing natronoarchaea were red-pigmented and surrounded by large zones of chitin hydrolysis. The free cells of both groups were mostly flat nonmotile rods, while the cells that attached to chitin or formed colonies on chitin plates were mostly coccoid. The isolates are obligate aerobic saccharolytic archaea utilizing chitin and chitosane (less actively) as the only sugar polymers as well as a few hexoses as their carbon and energy source. Both groups are extremely halophilic, growing optimally at 3.5-4M total Na+ , but they differ in their pH profiles: the main group 1 isolates are obligately alkaliphilic, while the single group 2 strain (AArcht-SlT ) is alkalitolerant. The core archaeal lipids in both groups are dominated by C20 -C20 and C20 -C25 dialkyl glycerol ethers (DGE) in approximately equal proportion. Phylogenetic analysis indicated that the isolates form an independent genus-level lineage within the family Natrialbaceae with 3 species-level subgroups. The available genomes of the closest cultured relatives of the AArcht strains, belonging to the genera Natrialba and Halopiger, do not encode any chitinase-related genes. On the basis of their unique phenotypic properties and distinct phylogeny, we suggest that the obligate alkaliphilic AArcht isolates (group 1) with an identical phenotype are classified into a new genus and species Natrarchaeobius chitinivorans gen. nov., sp. nov., with strain AArcht4T as the type strain (JCM 32476T =UNIQEM U966T ), while the facultatively alkaliphilic strain AArcht-SlT (group 2) - as a new species Natrarchaeobius halalkaliphilus sp. nov. (JCM 32477T =UNIQEM U969T ).