A Gram-negative, rod-shaped, non-pigmented, non-spore-forming bacterial strain that was motile by a single polar flagellum, designated A1-9(T), was isolated from Daqing reservoir in north-east China and its taxonomic position was studied using a polyphasic approach. Strain A1-9(T) was non-halophilic, strictly aerobic and heterotrophic and lacked carotenoids, internal membranes and genes for photosynthesis (puf genes). Strain A1-9(T) grew at 10-40 degrees C (optimum, 25-30 degrees C) and pH 5.5-9.0 (optimum, pH 6.0-6.5) and tolerated up to 1.0 % NaCl (w/v). Neither phototrophic nor fermentative growth was observed. The predominant ubiquinone was Q-10 and the major fatty acid was C(18 : 1) �s 7c (70 %). The DNA G+C content was 64.4 mol% (T(m)). Phylogenetic analyses based on the 16S rRNA gene sequence revealed that strain A1-9(T), together with Catellibacterium nectariphilum AST4(T), formed a deep line within the 'Rhodobacter clade' of the family Rhodobacteraceae and strain A1-9(T) showed 94.2 % 16S rRNA gene sequence similarity to C. nectariphilum AST4(T). On the basis of phenotypic, chemotaxonomic and phylogenetic data, strain A1-9(T) is considered to represent a novel species of the genus Catellibacterium, for which the name Catellibacterium aquatile sp. nov. is proposed. The type strain is A1-9(T) (=CGMCC 1.7029(T) =NBRC 104254(T)).