Three Gram-stain negative, aerobic, non-motile, non-spore-forming, rod-shaped bacterial strains, PYM5-11(T), RaM5-2 and PYM5-8, were isolated from the drinking water supply system of Budapest (Hungary) and their taxonomic positions were investigated by a polyphasic approach. All three strains grew optimally at 20-28°C and pH 5-7 without NaCl. The G+C content of the DNA of the type strain was 65.4mol%. On the basis of 16S rRNA gene sequence analysis, the isolates showed 94.5-94.9% sequence similarity to the type strain of Dokdonella koreensis and a similarity of 93.0-94.1% to the species of the genera Aquimonas and Arenimonas. The major isoprenoid quinone of the strains was ubiquinone Q-8. The predominant fatty acids were iso-C(15:0), iso-C(17:1)ω9c, C(16:1)ω7c, and C(16:0). Diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and phosphatidylmonomethylethanolamine, as well as several unidentified aminolipids and phospholipids were present. The 16S rRNA gene sequence analysis, the predominant fatty acids, the polar lipid composition, RiboPrint patterns, physiological and biochemical characteristics showed that the three strains were related but distinct from the type strains of the four recognized species of the genus Dokdonella, and indicated that the strains represented a new genus within the Gammaproteobacteria. The strain PYM5-11 (=DSM 21667(T)=NCAIM B 02337(T)) is proposed as the type strain of a new genus and species, designated as Tahibacter aquaticus gen. nov., sp. nov.