A light-yellow-pigmented bacterial strain designated JS43(T) was isolated from a freshwater spring in Taiwan and was characterized using a polyphasic taxonomic approach. Cells of strain JS43(T) were Gram-negative-staining, facultatively anaerobic, rod-shaped, non-motile and non-spore-forming. Growth occurred at 10-30 °C (optimum, 25 °C), at pH 7.0-10.0 (optimum, pH 7.0-8.0) and with 0-0.5 % (w/v) NaCl (optimum, 0 %). Phylogenetic analyses based on 16S rRNA gene sequences showed that strain JS43(T) was a member of the family Rhodobacteraceae of the class Alphaproteobacteria. Sequence similarities to type strains of the genera Gemmobacter and Catellibacterium were between 94.6 and 98.1 %. The highest sequence similarity was found with Gemmobacter aquatilis DSM 3857(T). Strain JS43(T) contained C(18 : 1)ω7c as the predominant fatty acid (74.4 %). The major isoprenoid quinone was Q-10 and the DNA G+C content was 69.3 mol%. The polar lipid profile consisted of a mixture of phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, two uncharacterized aminolipids and three uncharacterized phospholipids. The DNA-DNA relatedness values of strain JS43(T) with respect to the phylogenetically related Gemmobacter aquatilis DSM 3857(T), Catellibacterium aquatile A1-9(T) and Catellibacterium caeni DCA-1(T) were less than 70 %. The taxonomic relationship between members of the genera Gemmobacter and Catellibacterium was clarified by means of a direct experimental comparison. Based on phylogenetic, chemotaxonomic and phenotypic data, we propose that all species currently classified in the genus Catellibacterium should be transferred to the genusGemmobacter. The following new combinations are proposed: Catellibacterium nectariphilum is reclassified as Gemmobacter nectariphilus comb. nov. (type strain, AST4(T) = DSM 15620(T) = JCM 11959(T) = NBRC 100046(T)), Catellibacterium changlense as Gemmobacter changlensis comb. nov. (type strain, JA139(T) = CCUG 53722(T) = DSM 18774(T) = JCM 14338(T)), Catellibacterium aquatile as Gemmobacter aquaticus nom. nov. (type strain, A1-9(T) = CGMCC 1.7029(T) = NBRC 104254(T)), Catellibacterium caeni as Gemmobacter caeni comb. nov. (type strain, DCA-1(T) = CGMCC 1.7745(T) = DSM 21823(T)) and Catellibacterium nanjingense as Gemmobacter nanjingensis comb. nov. (type strain, Y12(T) = CCTCC AB 2010218(T) = KCTC 23298(T)). Emended descriptions of the genus Gemmobacter and of Gemmobacter aquatilis are also presented. Strain JS43(T) could be distinguished from recognized species of the genera Gemmobacter and Catellibacterium. It is suggested, on the basis of genotypic and phenotypic characteristics, that strain JS43(T) ( = BCRC 80082(T) = LMG 25376(T)) represents a novel species for which the name Gemmobacter fontiphilus is proposed.