Most species of haloarchaea, extremely halophilic members of the phylum Halobacteriota, known in pure culture have been retrieved and further cultivated using simple soluble organic compounds, such as sugars or organic acids or rich complex media based on amino acid mixtures. However, our recent exploration of the polysaccharide-utilizing potential of halo(natrono)archaea living in hypersaline salt and soda lakes using a targeted selective enrichment strategy allowed us to obtain a broad range of new isolates. These were both from already known genera and from several novel genus lineages, and were capable of hydrolysis and further utilization as a growth substrate of a wide spectrum of polysaccharides, including cellulose, chitin and various alpha-beta-linked glucans (Sorokin et al., 2015, Sorokin et al., 2018, Sorokin et al., 2019, Sorokin et al., 2022) (Sorokin et al., 2015; 2018; 2019; 2022). Two of the most difficult to utilize polysaccharides under hypersaline conditions were curdlan and pachyman, both insoluble beta-1,3-backbone-glucans from bacteria (the former) and fungi (the latter) with a helix-like secondary structure (Zhan et al., 2012, Zhang and Edgar, 2014). They are known substrates for fungal and bacterial glycoside hydrolases, belonging to the GH families 64, 81 and 128 (Pluvinage et al., 2017, Hettle et al., 2017). Some of those (according to the CAZy database (http://www.cazy.org)) are encoded in a few haloarchaeal genomes, such as the GH81 and 128 homologs. However, until now there was no clear evidence of the utilization of curdlan as a substrate and curdlan/pachyman hydrolyzing enzymes have not been identified in the Archaeal domain.

Our recent targeted enrichment cultivation approach allowed us, for the first time, to obtain in pure culture several strains of haloarchaea from hypersaline lakes which utilize curdlan and pachyman as growth substrates (Sorokin et al., 2022). This paper presents the results of the taxonomy characterization and functional genome analysis for two closely related salt lake isolates, forming a distinct novel species in the genus Halapricum.