Abstract
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.
Highlights
Tobacco products are among the most widely popular goods worldwide due to the addictive component in tobacco: nicotine
The draft genome sequence of S. melonis TY was obtained by Illumina sequencing, and blast searching of the sequence using representative sequences for nicotine-degrading enzymes from A. nicotinovorans and Ochrobactrum sp
S. melonis TY can degrade nicotine efficiently than many other nicotine degraders, and has tolerance to some neonicotinoid insecticides when degrading nicotine, which is suitable for the disposal of tobacco waste and the reduction of nicotine in tobacco leaves and this tolerance was not reported in other nicotine degraders (Wang et al, 2011)
Summary
Tobacco products are among the most widely popular goods worldwide due to the addictive component in tobacco: nicotine. Nicotine is the most abundant alkaloid in tobacco plants, and a large amount of tobacco waste produced every year is disseminated in the environment through water and soil. As important decomposers in ecosystems, microbes possess powerful, and versatile degradation capacities, as reflected in the type of substrates utilized, the metabolic mechanisms involved, and diversity of catalyzing enzymes. One example is the diversity in metabolic pathways and molecular mechanisms of nicotine degradation by microorganisms. Research on the microbial degradation of nicotine has been studied since the 1950s (Wada and Yamasaki, 1953). Various bacteria and fungi are reported to be able to decompose nicotine through at least six pathways, though there are four main degradation pathways. Various bacteria and fungi are reported to be able to decompose nicotine through at least six pathways, though there are four main degradation pathways. (1) The pyridine pathway, which begins with the
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