A Gram-negative, short, rod-shaped, floc-forming bacterium, strain RB3-7T, was isolated from a laboratory-scale activated sludge system treating coke plant effluent. Comparative analysis of the 16S rRNA gene sequence demonstrated that the novel isolate is distantly related (95.8 % similarity) to the type strain of Ottowia thiooxydans K11T within the family Comamonadaceae. The organism is catalase and oxidase positive and non-motile. The predominant fatty acids of RB3-7T are C16:0, cycloC17:0, C18:17c and C16:17c, and the major respiratory quinone is Q-8. The G + C content of the genomic DNA is 68.5 mol%. On the basis of the phenotypic, chemotaxonomic and molecular data, strain RB3-7T represents a novel species in the genus Ottowia, for which the name Ottowia pentelensis sp. nov. is proposed. The type strain is RB3-7T (=DSM 21699T=NCAIM B 02336T).