Regulators essential for nicotine degradation in Shinella sp. HZN7

• A mutant of Shinella sp. HZN7 which failed to degrade nicotine was screened.
• The two mutant genes composed a novel two-component regulatory system.
• The two genes were both essential for nicotine degradation.

Shinella sp. HZN7 can degrade nicotine via a variant of the pyridine and pyrrolidine pathways. In this study, a transposon mutant N7-W13 that was unable to degrade nicotine was identified and the mutant genes were cloned and sequenced. The predicted gene products ORFW13-1 and ORFW13-2 showed similarities to transcriptional regulatory proteins and sensor histidine kinases, respectively, which are constituents of typical two-component regulator systems. The orfW13-1 gene was interrupted by a transposon insertion in the strain N7-W13, while we constructed a strain with an orfW13-2 gene disruption, known as N7ΔorfW13-2. The mutants N7-W13 and N7ΔorfW13-2 all lost the ability to degrade nicotine, but were still capable of metabolizing 6-hydroxy-nicotine. These results suggest that the regulators are essential for nicotine degradation in Shinella sp. HZN7.

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