Abstract
Twenty-three novel psychrophilic bacteria, represented by the type strains LB2P44(T), LB2P6(T), LB1P62(T), LB3P6(T), LS1P3(T), XS2P39(T), XS1P32(T), ZB4P13(T), ZS1P14(T) and GT2P42(T), were isolated from ice, cryoconite and meltwater of five Tibetan Plateau glaciers. All strains were Gram-stain-negative, aerobic, rod-shaped and psychrophilic, with optimal growth at 14-20 °C and pH 7.0. 16S rRNA gene sequence similarities to validly named Flavobacterium species ranged from 98.12% to 99.56%. Phylogenomic analysis of 81 concatenated core genes positioned the 23 strains (comprising the ten novel species) within a robust monophyletic clade - the 'Cryospheric Lineage' - together with 31 other psychrophilic type strains predominantly from glaciers, permafrost and polar regions. Average nucleotide identity (ANI) values of ≤94.4% and digital DNA-DNA hybridization (dDDH) values of ≤57.3% against closest relatives were below species thresholds (95-96% ANI, 70% dDDH). Major fatty acids were iso-C(15:0) (8.1-16.8%), iso-C(15:0) 3-OH (3-hydroxy, 5.2-16.0%) and summed feature 3 (C(16:1) ω7c and/or C(16:1) ω6c, 10.1-27.6%), with elevated branched-chain and unsaturated components typical of cold adaptation. Polyphasic taxonomic evidence supports the description of ten novel species within the genus Flavobacterium: Flavobacterium amylolyticum sp. nov. (LB2P44(T)=CGMCC 1.11256(T)=NBRC 114815(T)), Flavobacterium glucosi sp. nov. (LB2P6(T)=CGMCC 1.11263(T)=NBRC 114816(T)), Flavobacterium esculini sp. nov. (LB1P62(T)=CGMCC 1.11346(T)=NBRC 114817(T)), Flavobacterium labens sp. nov. (LB3P6(T)=CGMCC 1.11428(T)=NBRC 114818(T)), Flavobacterium pasteuri sp. nov. (LS1P3(T)=CGMCC 1.11474(T)=NBRC 114821(T)), Flavobacterium rhamnosi sp. nov. (XS2P39(T)=CGMCC 1.23204(T)=NBRC 115054(T)), Flavobacterium frigidum sp. nov. (XS1P32(T)=CGMCC 1.23370(T)=NBRC 115055(T)), Flavobacterium glycogeni sp. nov. (ZB4P13(T)=CGMCC 1.24050(T)=NBRC 115056(T)), Flavobacterium kochi sp. nov. (ZS1P14(T)=CGMCC 1.24093(T)=NBRC 114828(T)) and Flavobacterium cryophilum sp. nov. (GT2P42(T)=CGMCC 1.24821(T)=NBRC 114831(T)).