A pyridine-degrading bacterial strain was isolated from the oxic zone of a spent share column. The microorganism was an aerobic and pleomorphic coryneform bacterium with LL-diaminopimelic acid in the cell wall. On the basis of its phylogenetic and chemotaxonomic characteristics, the strain was identified as Nocardioides sp. strain OS4. The pyridine was completely degraded and the growth yield was 0.30 g cell/g pyridine. Strain OS4 metabolized pyridine in an inducible manner and released a pigment that has maximum absorbance at 400 nm during the pyridine degradation. This strain also degraded some compounds of the basic fraction of retort water and various other aromatic compounds.