The genus Natronolimnobius, currently including four species, is a member of the order Natrialbales, class Halobacteria, and consists of obligately alkaliphilic and extremely halophilic members found exclusively in highly alkaline hypersaline soda lakes. The species were classified into this genus mostly based on phylogenetic analysis of the 16S rRNA gene. However, a more advanced phylogenomic reconstruction based on 122 conserved single-copy archaeal protein markers clearly indicates a polyphyletic origin of the species included into this genus, thus warranting its reclassification into three separate genera. We therefore propose to transfer Nlb. innermongolicus (type strain N-1311) to a new genus Natronolimnohabitans as Nlh. innermongolicus comb. nov. and to transfer Nlb. aegyptiacus (type strain JW/NM-HA 15) and Nlb. sulfurireducens (type strain AArc1) to a new genus Natrarchaeobaculum as Nbl. aegyptiacum comb. nov. and Nbl. sulfurireducens comb. nov. The phylogenomic differentiation of these four species is also supported by the ANI/AAI distances and unique phenotypes. The most important physiological differences includes a previously unreported ability for cellulose and xylan utilization in Nlb. baerhuensis, thermophily in Nbl. aegyptiacus and anaerobic sulfur respiration in Nbl. sulfurireducens. We further present an emended description of Natronolimnobius baerhuensis.@en

Na.tro.no.bi.for’ma. Gr. neut. n. natron arbitrarily derived from Arabic n. natrun or natron soda; L. adv. num. bis twice; L. fem. n. forma form, shape; N.L. fem. n. Natronobiforma the dimorphic natronoarchaeon. The genus Natronobiforma, classified within the family Natrialbaceae, order Natrialbales, in the class Halobacteria, currently consists of a single species, Natronobiforma cellulositropha. It is a moderately alkaliphilic, obligately aerobic, extreme halophile, forming pink colonies with large clearance zones on plates containing amorphous cellulose. The cells are pleomorphic flat motile rods or nonmotile coccoid cells. Multiple strains classified within this genus were isolated from alkaline hypersaline lakes in different locations. They grow optimally on insoluble native celluloses. Xylan, β-mannan, cellobiose, and maltose can also be used as carbon and energy sources. Other organic compounds used by most members of the Halobacteria do not support growth. DNA G+C content (mol%): 65.4–65.5 (genome sequences). Type species: Natronobiforma cellulositropha Sorokin et al. 2019, VL187.@en

Na.no.ha.lo’bi.um. Gr.masc. n. nanos a dwarf; Gr. masc. n. hals, halos salt; Gr. masc. n. bios life; N.L. neut. n. Nanohalobium small organism living in salt. The genus Candidatus Nanohalobium was established based on a genome sequence found after the enrichment, cultivation, and characterization of a binary association with its chitinolytic host, obtained from a crystallizer pond brine collected in the marine solar saltern Saline della Laguna of Trapani, Italy. Ca. Nanohalobium is phylogenetically affiliated with members of the Ca. Nanohaloarchaeota (Candidatus Haloredivivus, Candidatus Nanosalina, and Candidatus Nanosalinicola) of the archaeal DPANN superphylum. Cultivation experiments and analysis of the 0.97Mb genome of Ca. Nanohalobium constans LC1Nh revealed that the organism has an organoheterotrophic, sugar-fermenting lifestyle, lacking key anabolic machinery and any respiratory complexes. Additionally, the cultivation experiments revealed a remarkable mutualism of a nanohaloarchaeon–haloarchaeon association, namely the nanohaloarchaeon’s ability to hydrolyze glycogen and starch to glucose, enabling the growth of Halomicrobium sp. LC1Hm in the absence of chitin. The low-median isoelectric point for the predicted proteins suggests a “salt-in” strategy used by the nanohaloarchaeon for osmotic balance. 16S rRNA gene sequences affiliated with Ca. Nanohalobium were recovered from other saltern ponds and hypersaline lakes worldwide. DNA G+C content (mol%): 43.2 (genome). Type species: Candidatus Nanohalobium constans, La Cono et al. 2020.@en

Na.no.ha.lo’bi.um. Gr.masc. n. nanos a dwarf; Gr. masc. n. hals, halos salt; Gr. masc. n. bios life; N.L. neut. n. Nanohalobium small organism living in salt. The genus Candidatus Nanohalobium was established based on a genome sequence found after the enrichment, cultivation, and characterization of a binary association with its chitinolytic host, obtained from a crystallizer pond brine collected in the marine solar saltern Saline della Laguna of Trapani, Italy. Ca. Nanohalobium is phylogenetically affiliated with members of the Ca. Nanohaloarchaeota (Candidatus Haloredivivus, Candidatus Nanosalina, and Candidatus Nanosalinicola) of the archaeal DPANN superphylum. Cultivation experiments and analysis of the 0.97Mb genome of Ca. Nanohalobium constans LC1Nh revealed that the organism has an organoheterotrophic, sugar-fermenting lifestyle, lacking key anabolic machinery and any respiratory complexes. Additionally, the cultivation experiments revealed a remarkable mutualism of a nanohaloarchaeon–haloarchaeon association, namely the nanohaloarchaeon’s ability to hydrolyze glycogen and starch to glucose, enabling the growth of Halomicrobium sp. LC1Hm in the absence of chitin. The low-median isoelectric point for the predicted proteins suggests a “salt-in” strategy used by the nanohaloarchaeon for osmotic balance. 16S rRNA gene sequences affiliated with Ca. Nanohalobium were recovered from other saltern ponds and hypersaline lakes worldwide. DNA G+C content (mol%): 43.2 (genome). Type species: Candidatus Nanohalobium constans, La Cono et al. 2020.@en