Conversion of nornicotine to 6-hydroxy-nornicotine and 6-hydroxy-myosmine by <Emphasis Type="Italic">Shinella</Emphasis> sp. strain HZN7 |
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Authors: | Jiguo Qiu Na Li Zhenmei Lu Youjian Yang Yun Ma Lili Niu Jian He Weiping Liu |
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Institution: | 1.Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Sciences,Nanjing Agricultural University,Nanjing,China;2.College of Life Sciences,Zhejiang University,Hangzhou,China;3.College of Environment,Zhejiang University of Technology,Hangzhou,China;4.College of Environmental and Resource Sciences,Zhejiang University,Hangzhou,China |
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Abstract: | Nornicotine is a natural alkaloid produced by plants in the genus Nicotiana and is structurally related to nicotine. Importantly, nornicotine is the direct precursor of tobacco-specific nitrosamine N′-nitrosonornicotine, which is a highly potent human carcinogen. Microbial detoxification and degradation of nicotine have been well characterized; however, until now, there has been no information on the molecular mechanism of nornicotine degradation. In this study, we demonstrate the transformation of nornicotine by the nicotine-degrading strain Shinella sp. HZN7. Three transformation products were identified as 6-hydroxy-nornicotine, 6-hydroxy-myosmine, and 6-hydroxy-pseudooxy-nornicotine by UV spectroscopy, high-resolution mass spectrometry, nuclear magnetic resonance, and Fourier transform-infrared spectroscopy analyses. The two-component nicotine dehydrogenase genes nctA1 and nctA2 were cloned, and their product, NctA, was confirmed to be responsible for the conversion of nornicotine into 6-hydroxy-nornicotine as well as nicotine into 6-hydroxy-nicotine. The 6-hydroxy-nicotine oxidase, NctB, catalyzed the oxidation of 6-hydroxy-nornicotine to 6-hydroxy-myosmine, and it spontaneously hydrolyzed into 6-hydroxy-pseudooxy-nornicotine. However, 6-hydroxy-pseudooxy-nornicotine could not be further degraded by strain HZN7. This study demonstrated that nornicotine is partially transformed by strain HZN7 via nicotine degradation pathway. |
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