Characterization of a Novel Nicotine Degradation Gene ClusterndpinSphingomonas melonisTY and Its Evolutionary Analysis.
Sphingomonas melonisTY utilizes nicotine as a sole source of carbon, nitrogen, and energy through a variant of the pyridine and pyrrolidine pathways (VPP). A 31-kb novel nicotine-degrading gene cluster,ndp, in strain TY exhibited a different genetic organization with thevppcluster in strainsOchrobactrum rhizosphaeraeSJY1 andAgrobacterium tumefaciensS33. Genes invppwere separated by a 20-kb interval sequence, while genes inndpwere localized together. Half of the homolog genes were in different locus inndpandvpp. Moreover, there was a gene encoding putative transporter of nicotine or other critical metabolite inndp. Among the putative nicotine-degrading related genes, the nicotine hydroxylase, 6-hydroxy-L-nicotine oxidase, 6-hydroxypseudooxynicotine oxidase, and 6-hydroxy-3-succinyl-pyridine monooxygenase responsible for catalyzing the transformation of nicotine to 2, 5-dihydropyridine in the initial four steps of the VPP were characterized. Hydroxylation at C6 of the pyridine ring and dehydrogenation at the C2-C3 bond of the pyrrolidine ring were the key common reactions in the VPP, pyrrolidine and pyridine pathways. Besides, VPP and pyrrolidine pathway shared the same latter part of metabolic pathway. After analysis of metabolic genes in the pyridine, pyrrolidine, and VPP pathways, we found that both the evolutionary features and metabolic mechanisms of the VPP were more similar to the pyrrolidine pathway. The linkedndpHFEGgenes shared by the VPP and pyrrolidine pathways indicated that these two pathways might share the same origin, but variants were observed in some bacteria. And we speculated that the pyridine pathway was distributed in Gram-positive bacteria and the VPP and pyrrolidine pathways were distributed in Gram-negative bacteria by using comprehensive homologs searching and phylogenetic tree construction.
Institute of Microbiology, College of Life Sciences, Zhejiang University Hangzhou, China.
Haixia
H
Wang
Yunnan Institute of Microbiology, School of Life Sciences, Yunnan University Kunming, China.
Xiao-Yang
XY
Zhi
Department of Microbiology, College of Life Sciences, Nanjing Agricultural University Nanjing, China.
Jiguo
J
Qiu
Institution of System Engineering, College of Computer Science and Technology, Zhejiang University Hangzhou, China.
Longxiang
L
Shi
Institute of Microbiology, College of Life Sciences, Zhejiang University Hangzhou, China.
Zhenmei
Z
Lu
Sphingomonas melonis TY; ndp gene cluster; nicotine; pathway distribution; pathway evolution