Wang Haixia, Zhi Xiao-Yang, Qiu Jiguo, Shi Longxiang, Lu Zhenmei
Institute of Microbiology, College of Life Sciences, Zhejiang University Hangzhou, China.
Yunnan Institute of Microbiology, School of Life Sciences, Yunnan University Kunming, China.
Front Microbiol. 2017 Mar 9;8:337. doi: 10.3389/fmicb.2017.00337. eCollection 2017.
TY 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, , in strain TY exhibited a different genetic organization with the cluster in strains SJY1 and S33. Genes in were separated by a 20-kb interval sequence, while genes in were localized together. Half of the homolog genes were in different locus in and . Moreover, there was a gene encoding putative transporter of nicotine or other critical metabolite in . 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 linked genes 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.
菌株TY通过吡啶和吡咯烷途径变体（VPP）将尼古丁作为唯一的碳、氮和能量来源。菌株TY中一个31 kb的新型尼古丁降解基因簇与菌株SJY1和S33中的簇具有不同的基因组织。中的基因被一个20 kb的间隔序列隔开，而中的基因则定位在一起。一半的同源基因在和中的位置不同。此外，中有一个编码尼古丁或其他关键代谢物假定转运蛋白的基因。在假定的尼古丁降解相关基因中，对负责在VPP的最初四个步骤中将尼古丁转化为2,5 - 二氢吡啶的尼古丁羟化酶、6 - 羟基 - L - 尼古丁氧化酶、6 - 羟基假氧尼古丁氧化酶和6 - 羟基 - 3 - 琥珀酰 - 吡啶单加氧酶进行了表征。吡啶环C6位的羟基化和吡咯烷环C2 - C3键的脱氢是VPP、吡咯烷和吡啶途径中的关键共同反应。此外，VPP和吡咯烷途径共享代谢途径的后半部分。通过对吡啶、吡咯烷和VPP途径中的代谢基因进行分析，我们发现VPP的进化特征和代谢机制与吡咯烷途径更为相似。VPP和吡咯烷途径共享的连锁基因表明这两条途径可能具有相同的起源，但在一些细菌中观察到了变体。并且我们推测通过全面的同源物搜索和系统发育树构建，吡啶途径分布在革兰氏阳性细菌中，而VPP和吡咯烷途径分布在革兰氏阴性细菌中。
