Identification and Characterization of hmr19 Gene Encoding a Multidrug Resistance Efflux Protein from Streptomyces hygroscopicus subsp. yingchengensis Strain 10-22

The hmr19 gene was cloned from Streptomyces hygroscopicus subsp, yingchengensis strain 10-22, a bacterium strain producing agricultural antibiotics. Sequence similarity comparison indicates that hmr19 gene may encode a predicted protein with 14 putative transmembrane s-helical spanners, belonging to the drug:H^+ antiporter-2 family of the major facilitator superfamily. The expression ofhmr19 in the mycelium of strain 10-22 was detected by Western blotting analysis. Gene replacement technology was employed to construct an hmrl9 disruption mutant. The growth inhibition test against different antibiotics indicated that the mutant strain was 5-20 fold more susceptible to tetracycline, vancomycin and mitomycin C than the parental wild type strain. The mutant took up tetracycline much faster and accumulated more antibiotics than the wild type strain 10-22. While with the addition of an energy uncoupler, carbonyl cyanide mchlorophenylhydrazone, the characteristics of the accumulation of [3H]tetracycline in these two strains were almost the same. It was thus concluded that hmr19 encoded a multidrug resistance efflux protein.