ABSTRACT
Nicotine is a natural alkaloid produced by tobacco plants, and the mechanisms of its catabolism by microorganisms are diverse. In the present study, we reported the mutation, cloning, and identification of two novel genes involved in nicotine degradation from the newly isolated
Pseudomonas
sp. strain HZN6. Transposon mutagenesis identified a HZN6 mutant in which the nicotine-degrading pathway was blocked at pseudooxynicotine. A 3,874-bp DNA fragment flanking the transposon insertion site was obtained through self-formed adaptor PCR. Two open reading frames (designated
pao
and
sap
) were analyzed, and the deduced amino acid sequences shared 29% identity with 6-hydroxy-
l
-nicotine oxidase from
Arthrobacter nicotinovorans
and 49% identity with an aldehyde dehydrogenase from
Bartonella henselae
. Both
pao
and
sap
were cloned and functionally expressed in recombinant
Escherichia coli
BL21. The
pao
gene encoded a novel pseudooxynicotine amine oxidase with noncovalently bound flavin adenine dinucleotide (FAD) and exhibited substrate specificity removing the methylamine from pseudooxynicotine with the formation of 3-succinoylsemialdehyde-pyridine and hydrogen dioxide. The
sap
gene encoded a NADP
+
-dependent 3-succinoylsemialdehyde-pyridine dehydrogenase that catalyzed the dehydrogenation of 3-succinoylsemialdehyde-pyridine to 3-succinoyl-pyridine. Genetic analyses indicated that the
pao
gene played an essential role in nicotine or pseudooxynicotine mineralization in strain HZN6, whereas the
sap
gene did not. This study provides novel insight into the nicotine-degrading mechanism at the genetic level in
Pseudomonas
spp.
摘要
尼古丁是烟草植物产生的一种天然生物碱,其被微生物分解的机制多种多样。在本研究中,我们报道了从新分离的假单胞菌中突变、克隆和鉴定出两个参与尼古丁降解的新基因。
假单胞菌
菌株 HZN6 中参与尼古丁降解的两个新基因的突变、克隆和鉴定。转座子诱变鉴定出了一个 HZN6 突变体,在该突变体中,尼古丁降解途径在假烟碱处被阻断。通过自成适配体的聚合酶链式反应(PCR),获得了转座子插入位点侧翼的 3,874 bp DNA 片段。两个开放阅读框(指定为
pao
和
sap
) 进行了分析,推导出的氨基酸序列与 6-hydroxy- lap
l
-尼古丁氧化酶
的 6-羟基-l-尼古丁氧化酶有 29%的相同性,与
的醛脱氢酶有 49% 的相同度
的醛脱氢酶
.这两个
和
和
sap
都被克隆并在重组的
大肠杆菌
BL21。该
pao
基因编码一种新型假烟碱胺氧化酶,该酶与黄素腺嘌呤二核苷酸(FAD)非共价结合,具有底物特异性,能从假烟碱中去除甲胺,生成 3-丁二酰基半醛吡啶和二氧化氢。该
汁液
基因编码一种 NADP
+
-依赖的 3-琥珀酰半乳糖醛吡啶脱氢酶,该酶催化 3-琥珀酰半乳糖醛吡啶脱氢为 3-琥珀酰吡啶。遗传分析表明
pao
基因在 HZN6 菌株的尼古丁或假烟碱矿化过程中起着重要作用,而
sap
基因则不起作用。这项研究从基因水平上对假单胞菌的尼古丁降解机制提供了新的见解。
假单胞菌
的尼古丁降解机制提供了新的见解。