Identification and characterization of Nornicotine degrading strain Arthrobacter sp. NOR5

Highlights: • Arthrobacter sp. strain NOR5 could utilize nornicotine as the sole carbon source. • Novel metabolite 2,6DHPONor was detected during nornicotine degradation. • 6HPONor dehydrogenase activity was determined for the first time. • Strain NOR5 exhibited good potential for nornicotine bioremediation. 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.