Flavobacterium algoriphilum sp. nov., Flavobacterium arabinosi sp. nov., Flavobacterium cryoconiti sp. nov., Flavobacterium galactosi sp. nov., Flavobacterium melibiosi sp. nov., and Flavobacterium algoris sp. nov., six novel cold-adapted bacteria isolated from glaciers.

Background: Six novel cold-adapted bacteria, LB3P122, LT1R49, ZT3R17, ZT3R25, XS2P12, and GB2R13, were isolated from glaciers on the Tibetan Plateau. This study aimed to characterize their taxonomic status and elucidate their molecular adaptations to cold environments using a polyphasic approach.

Results: All strains were Gram-stain-negative, rod-shaped, and psychrophilic, growing at 0 °C with an optimum at 14-20 °C and at pH values of 6.0-8.0 (optimum pH 7.0). Analysis of the 16S rRNA gene sequences placed their taxonomic positions within the genus Flavobacterium, with similarities ranging from 97.2 to 98.4% to species with validly published names. Phylogenetic analysis of the 16S rRNA gene sequences revealed that the six strains formed distinct clades with Flavobacterium gawalongense GSP16. Phylogenomic analysis showed that these strains clustered with Flavobacterium gawalongense GSP16 and exhibited a close relationship with Flavobacterium urumqiense CGMCC 1.9230 and Flavobacterium xinjiangense CGMCC 1.2749. Average nucleotide identity (ANI) values ranging from 82.5 to 93.6% and digital DNA-DNA hybridization (dDDH) values ranging from 26.1 to 51.5% between these strains and their closest relatives were well below the bacterial species delineation thresholds (95-96% ANI, 70% dDDH). The predominant fatty acids were iso-C and summed feature 3 (C ω7c and/or C ω6c). Genomic analysis identified genes associated with cryoprotection, oxidative stress response, cold-shock response, and osmoprotection in these strains, underscoring their adaptations to glacial environments.

Conclusions: Based on polyphasic taxonomic evidence, the strains represent six novel species within the genus Flavobacterium, with the proposed names Flavobacterium algoriphilum sp. nov. (LB3P122 = CGMCC 1.11443 = NBRC 114820), Flavobacterium arabinosi sp. nov. (LT1R49 = CGMCC 1.11617 = NBRC 114822), Flavobacterium cryoconiti sp. nov. (ZT3R17 = CGMCC 1.11707 = NBRC 114824), Flavobacterium galactosi sp. nov. (ZT3R25 = CGMCC 1.11711 = NBRC 114825), Flavobacterium melibiosi sp. nov. (XS2P12 = CGMCC 1.23198 = NBRC 114826), and Flavobacterium algoris sp. nov. (GB2R13 = CGMCC 1.24741 = NBRC 114830). These findings enhance our understanding of Flavobacterium diversity and cold adaptation in cryospheric ecosystems.