Characterization of phenotype and expression regulation of an RND-type multidrug efflux pump in Mesorhizobium huakuii 7653R

Abstract:

[Objective] To study the function of an RND family efflux pump encoded by MCHK_0866 and MCHK_0867 in Mesorhizobium huakuii 7653R. [Methods] Genetic organization of target genes was analyzed in genome. The change of growth was observed by measuring OD₆₀₀. Drug sensitivity was detected by minimal inhibitory concentrations; relative transcription level of target genes was measured by RT-PCR. Transcript regulation of the efflux pump was validated by bacterial one-hybrid system. [Results] Proteins encoded by MCHK_0866 and MCHK_0867 formed an RND family efflux pump. The OD₆₀₀ of growth curve reduced and it showed more sensitivity to nalidixic acid, tetracycline and SDS after disrupting the efflux pump. Genes relative transcription level increased in response to nalidixic acid treatment. Meanwhile, the downstream gene MCHK_0869 belongs to TetR family transcription factor and its expression product can interact with the promoter region of MCHK_0867. [Conclusion] The efflux pump is possibly associated with the transportation of nalidixic acid and affects rhizobial free-living growth. The pump is putatively regulated by a downstream local transcription factor.

Key words:Mesorhizobium huakuii 7653R;resistance nodulation cell division;efflux pump;nalidixic acid