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Nicotine is a type of environmental pollutant present in the tobacco waste that is generated during tobacco manufacturing.  Sphingomonas melonis  TY can utilize nicotine as a sole source of carbon, nitrogen and energy via a variant of the pyridine and pyrrolidine pathway (the VPP pathway). In this study, we report the identification of two novel sets of genes,  ndrA1A2A3 , and  ndrB1B2B3B4 , which are crucial for nicotine degradation by strain TY.  ndrA1A2A3  and  ndrB1B2B3B4  exhibit similarity with both nicotine dehydrogenase  ndh  from  Arthrobacter nicotinovorans  and nicotine hydroxylase  vppA  from  Ochrobactrum  sp. SJY1. The transcriptional levels of  ndrA1A2A3  and  ndrB1B2B3B4  in strain TY were significantly upregulated in the presence of nicotine. Furthermore,  ndrA1  or  ndrB2  knockout resulted in a loss of the ability to degrade nicotine, whereas gene complementation restored the capacity of each mutant to utilize nicotine for growth. Biodegradation assays indicated that the mutant strains retained the ability to degrade the first intermediate in the pathway, 6-hydroxynicotine (6 HN). However, heterologous expression of  ndrA1A2A3  and  ndrB1B2B3B4  did not confer nicotine dehydrogenase activity to  E. coli  DH5α,  Pseudomonas putida  KT2440 or  Sphingomonas aquatilis . These results provide information on the VPP pathway of nicotine degradation in  S. melonis  TY, and we conclude that these two sets of genes have essential functions in the conversion of nicotine to 6 HN in strain TY.

Two Novel Sets of Genes Essential for Nicotine Degradation by Sphingomonas melonis TY