Nicotine is a major alkaloid produced by the tobacco plant and the main harmful chemical in tobacco waste.Sphingomonas sp.TY can degrade nicotine into non-toxic compounds efficiently through variations of the pyridine and pyrrolidine pathway.We found a 31-kb gene cluster ndp containing seven genes involved in nicotine metabolism and transport.Two genes designated ndpB and ndpT were knockout respectively and both of them were found to be critical for the nicotine metabolism in strain TY.