A pyridine-degrading strain was isolated from the contaminated soil near the pesticide plant, identified as Paracoccus sp., and designated as strain KT-5, on the basis of its partial 16S rRNA gene sequence analysis. The effect of different co-substrates including glucose, ammonium chloride and trace elements on biodegradation of pyridine by Paracoccus sp. KT-5 was investigated. The results showed that when the initial concentration of pyridine was about 900 mg L-1, 100 mg L-1 of glucose increased the growth of strain KT-5 and the removal of pyridine. but did not affect the release of nitrogen in the pyridine ring as ammonia. In addition, strain KT-5 was able to utilize 100 mg L-1 of glucose and 900 mg L-1 of pyridine simultaneously as the carbon source. 100 mg L-1 of ammonium chloride inhibited the growth of strain KT-5 in 900 mgL(-1) of pyridine, and also slightly decreased the removal of pyridine, but did not affect the release of nitrogen in the pyridine ring as ammonia. However, lacking of trace elements not only inhibited the growth of strain KT-5 in 900 mgL(-1) of pyridine, but also decreased the removal of pyridine, while it did not affect the release of nitrogen in the pyridine ring as ammonia. (C) 2009 Elsevier B.V. All rights reserved.