The taxonomy of two strains W-51T and W-52 isolated from a wastewater treatment plant was investigated in a polyphasic approach. The yellow pigmented gram-negative organism contained a quinone system with mainly ubiquinone Q-10, and the polar lipid profile contained a sphingoglycolipid suggesting that both strains belonged to the the alpha-4 subclass of the Proteobacteria. The polar lipid profile consisted furthermore of phosphatidylethanolamine, diphosphatidylglycerol, and phosphatidylcholine and of minor amounts of phosphatidylglycerol and phosphatidylmonomethylethanolamine. Sequencing of the 16S rRNA gene supported the allocation into the genus Novosphingobium, together with the type strains of N. subterraneum, N. aromaticivorans, N. stygium, and N. capsulatum, showing similarities of 97.3%, 97.0%, 95.7% and 96.2%, respectively. This allocation was supported by the polyamine profile, which consisted mainly of spermidine. The analysis of the fatty acids revealed 2-OH 13:0, 2-OH 14:0 and 2-OH 15:0, with 2-OH 15:0 as predominant hydroxylated fatty acid. W-51T and W-52 were almost identical with respect to their phenotypic including the majority of the chemotaxonomic properties, identical in their 16S rRNA sequences, and showed 86% DNA-DNA similarity. Both strains were able to reduce nitrate and on the basis of further physiological features, a clear differentiation from all other Novosphingobium species was possible. The DNA-DNA similarities of W-51T to the type strains of N. subterraneum, N. aromaticivorans, and N. capsulatum were below 56%. For these reasons, it is proposed to create a new species with the name Novosphingobium hassiacum sp. nov.