Conversion of nornicotine to 6-hydroxy-nornicotine and 6-hydroxy-myosmine by Shinella sp. strain HZN7
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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.
KeywordsNornicotine 6-Hydroxy-nornicotine 6-Hydroxy-myosmine 6-Hydroxy-pseudooxy-nornicotine Nicotine dehydrogenase 6-Hydroxy-nicotine oxidase Shinella sp. HZN7
This work was supported by the National Natural Science Foundation of China (Nos. 31500082 and 31422003), China Postdoctoral Science Foundation (No. 2014 M560495), and the Program for New Century Excellent Talents in University (NCET-13-0861).
Compliance with ethical standards
This article does not contain any studies with human participants or animals performed by any of the authors.
Conflict of interest
The authors declare that they have no conflict of interest.
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