Microbial degradation and metabolic pathway of pyridine by a <Emphasis Type="Italic">Paracoccus</Emphasis> sp. strain BW001

A bacterial strain using pyridine as sole carbon, nitrogen and energy source was isolated from the activated sludge of a coking wastewater treatment plant. By means of morphologic observation, physiological characteristics study and 16S rRNA gene sequence analysis, the strain was identified as the species of Paracoccus. The strain could degrade 2,614 mg l⁻¹ of pyridine completely within 49.5 h. Experiment designed to track the metabolic pathway showed that pyridine ring was cleaved between the C₂ and N, then the mineralization of the carbonous intermediate products may comply with the early proposed pathway and the transformation of the nitrogen may proceed on a new pathway of simultaneous heterotrophic nitrification and aerobic denitrification. During the degradation, NH₃-N occurred and increased along with the decrease of pyridine in the solution; but the total nitrogen decreased steadily and equaled to the quantity of NH₃-N when pyridine was degraded completely. Adding glucose into the medium as the extra carbon source would expedite the biodegradation of pyridine and the transformation of the nitrogen. The fragments of nirS gene and nosZ gene were amplified which implied that the BW001 had the potential abilities to reduce NO₂ ⁻ to NO and/or N₂O, and then to N₂.