Comparative Genomic Analyses of the Genus Unravels the Genomic Adaptation to Polar Extreme Environments.

The members of the genus have been isolated from various habitats, like saline soil, salt lake, sponge-associated and the human gut, some of which are even located in polar areas. To identify their stress resistance mechanisms and draw a genomic profile across this genus, we isolated four strains from the lakes in the Tibetan Plateau, referred to as the third pole, and compared them with all other 30 high-quality genomes that are deposited in NCBI. The Heaps' law model estimated that the pan-genome of this genus is open and the number of core, shell, cloud, and singleton genes were 993 (6.61%), 2782 (18.52%), 4117 (27.40%), and 7132 (47.47%), respectively. Phylogenomic and ANI/AAI analysis indicated that all genomes can be divided into three main clades, named NES-1, NES-2, and NES-3. The strains isolated from lakes in the Tibetan Plateau were clustered with four strains from different sources in the Antarctic and formed a subclade within NES-2, described as NES-AT. Genome features of this subclade, including GC (guanine + cytosine) content, tRNA number, carbon/nitrogen atoms per residue side chain (C/N-ARSC), and amino acid composition, in NES-AT individuals were significantly different from other strains, indicating genomic adaptation to cold, nutrient-limited, osmotic, and ultraviolet conditions in polar areas. Functional analysis revealed the enrichment of specific genes involved in bacteriorhodopsin synthesis, biofilm formation, and more diverse nutrient substance metabolism genes in the NES-AT clade, suggesting potential adaptation strategies for energy metabolism in polar environments. This study provides a comprehensive profile of the genomic features of the genus and reveals the possible mechanism for the survival of isolates in polar areas.