Identification and characterization of Nornicotine degrading strain Arthrobacter sp. NOR5

Nornicotine, the primary nicotine metabolite that is formed through demethylation of nicotine in the genus Nicotiana tabacum L. Nornicotine is not only a precursor of tobacco-specific nitrosamine N-nitrosonornicotine but also have detrimental effects to human health. Till now, information on the biotransformation of nornicotine is limited. Herein, we identified and characterized a bacterium Arthrobacter sp. strain NOR5, utilized nornicotine as the sole of carbon and energy source, and degraded 500 mg/L nornicotine completely within 60 h under the optimum conditions of pH 7.0 and 30 °C. In this study, we not only identified previously reported intermediate metabolites such as 6-OH-nornicotine, 6-OH-mysomine, 6-OH-pseudooxy-nornicotine (6HPONor) but also identified a new intermediate metabolite 2,6-di-OH-pseudooxy-nornicotine (2,6DHPONor) by UV spectroscopy and liquid chromatography coupled with time of flight mass spectrometry. About half of 6HPONor could be transformed into 2,6DHPONor that was identified as a novel catabolic intermediate of nornicotine. By the addition of an electron acceptor 2,6-dichlorophenolindophenol (DCIP), the cell-free extract exhibited inducible 6HPONor dehydrogenase activity at 179 ± 60 mU/mg that could convert 6HPONor to 2,6DHPONor. Our study demonstrated that Arthrobacter sp. strain NOR5 has a high potential to degrade the nornicotine completely.