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

Abstract Two groups of alkaliphilic haloarchaeafrom hypersaline alkaline lakes in Central Asia, Egypt and North America were enriched and isolated in pure culture using chitinas growth substrate. These cultures, termed AArcht, were divided into two groups: group 1 which includes eleven isolates from highly alkaline soda lakesand 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 chitinhydrolysis. The free cells of both groups were mostly flat nonmotile rods, while the cells that attached to chitinor formed colonies on chitinplates were mostly coccoid. The isolates are obligate aerobicsaccharolytic archaea utilizing chitinand 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 3.5–4 M total Na + , but they differ in their pH profiles: the main group 1 isolates are obligately alkaliphilic, while the single group 2 strain (AArcht-Sl T ) is alkalitolerant. The core archaeal lipids in both groups are dominated by C 20 –C 20 and C 20 –C 25 dialkyl glycerol ethers (DGE) in approximately equal proportion. Phylogenetic analysis indicated that the isolates form an independent genus-level lineage within the family Natrialbaceaewith 3 species-level subgroups. The available genomes of the closest cultured relatives of the AArcht strains, belonging to the genera Natrialbaand Halopiger, do not encode any chitinase-related genes. On the basis of their unique phenotypic properties and distinct phylogeny, we suggest that the obligate alkaliphilicAArcht isolates (group 1) with an identical phenotype are classified into a new genus and species Natrarchaeobius chitinivorans gen. nov., sp. nov., with strain AArcht4 T as the type strain (JCM 32476 T = UNIQEM U966 T ), while the facultatively alkaliphilicstrain AArcht-Sl T( group2) — as a new species Natrarchaeobius halalkaliphilus sp. nov. (JCM 32477 T = UNIQEM U969 T ).