Mesocryomonas lacus sp. nov. and Mesocryomonas fontinalis sp. nov., two novel species of the genus Mesocryomonas isolated from Xizang

Three bacterial strains, designated RWH2-10P3 ^T , RWH1-P55 and W4-P8 ^T , were isolated from water samples collected from Xizang Autonomous Region, China. Phylogenetic analysis based on 16S rRNA gene sequences revealed that all three strains belong to the genus Mesocryomonas , with the highest sequence similarities to Mesocryomonas glaciei B5-2 ^T (98.1–98.4%), according to the EzBioCloud database. The draft genomes of the three strains were fully assembled, with genome sizes of 5.16–5.30 Mb and DNA G+C contents of 66.0–66.3%. Phylogenomic analysis based on single-copy genes confirmed that strains RWH2-10P3 ^T and RWH1-P55 would form a distinct clade, and strain W4-P8 ^T clustered together as a separate clade within the genus Mesocryomonas . Genome-scale comparative taxonomic analyses, including the digital DNA–DNA hybridization values, average nucleotide identity values and average amino acid identity, showed that the corresponding values between the novel strains and the closest relative species M. glaciei B5-2 ^T were below 23.2, 80.1 and 76.6%, respectively, which were well below the species delineation thresholds. Chemotaxonomic analysis showed that the major fatty acids of novel strains were summed feature 8 (C _18 : 1  ω7 c and/or C _18 : 1  ω6 c). The predominant isoprenoid quinone was Q-10, and the major polar lipids included phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, sulfoquinovosyldiacylglycerol and several unidentified lipids. Phenotypically, the novel strains exhibited distinct characteristics in growth conditions, carbon source utilization and enzyme activities compared to closely related species. Based on the polyphasic taxonomic data, strains RWH2-10P3 ^T and RWH1-P55 represent one novel species, named Mesocryomonas lacus sp. nov., with the type strain RWH2-10P3 ^T (=CGMCC 1.66487 ^T =KCTC 18568 ^T ) and the strain RWH1-P55 (=CGMCC 1.66488=KCTC 18566). Strain W4-P8 ^T represents another novel species, for which the name Mesocryomonas fontinalis sp. nov. is proposed, with the type strain W4-P8 ^T (=CGMCC 1.66489 ^T =KCTC 18567 ^T ).