Candidatus Nanohalobium

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 estab- lished 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. Nanohalo- bium constans LC1Nh revealed that the organ- ism 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 glyco- gen 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 nanohaloar- chaeon 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.