AFrancisella-like bacterium, designated strain SYSU HZH-2T, was isolated from a water sample collected from Haizhu Lake, Guangzhou, China. The bacterium was fastidious, and required an exogenous source of l-cysteine for its growth on artificial media. Cells were Gram-stain-negative, coccobacilli, non-motile and non-spore-forming. The strain shared highest 16S rRNA gene sequence similarities with Cysteiniphilum litorale SYSU D3-2T (94.6 % identity), Fangia hongkongensis UST040201-002T (93.2 %) and Caedibacter taeniospiralis 51T (91.6 %). This strain possessed ubiquinone-8 as the respiratory quinone; diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine and phosphatidylglycerol as the known polar lipids, and anteiso-C15 : 0 and C18 : 0 as the major fatty acids (>10 % of total fatty acids). The dendrograms based on 16S rRNA gene sequence analysis showed that it formed a separate cluster along with Cysteiniphilum litorale SYSU D3-2T, Caedibactertaeiniospiralis 51T and Fangia hongkongensis UST040201-002T. Based on the 16S rRNA gene sequence identity and differences in other phenotypic characteristics, the strain is considered to represent a novel species of a novel genus, for which the name Fastidiosibacter lacustris gen. nov., sp. nov. is proposed. The type strain of the type species Fastidiosibacter lacustris is SYSU HZH-2T (=NBRC 112274T = CGMCC 1.15950T). Additionally, the new taxon along with the genera Caedibacter, Cysteiniphilum and Fangia (family unassigned) were distinctly separated from the related families Francisellaceae, Piscirickettsiaceae and Thiotrichaeae in the phylogenetic trees. Therefore, we proposed a new family Fastidiosibacteraceae fam. nov. within the order Thiotrichales to accommodate these four genera.
Keywords: Fastidiosibacter lacustris gen. nov., sp. nov.; Fastidiosibacteraceae fam. nov.; Haizhu Lake.