Abstract
Genes (ebrAB) responsible for ethidium resistance were cloned from chromosomal DNA of Bacillus subtilis ATCC 9372. The recombinant plasmid produced elevated resistance against ethidium bromide, acriflavine, pyronine Y, and safranin O not only in Escherichia coli but also in B. subtilis. It also caused an elevated energy-dependent efflux of ethidium in E. coli. EbrA and EbrB showed high sequence similarity with members of the small multidrug resistance (SMR) family of multidrug efflux pumps. Neither ebrA nor ebrB was sufficient for resistance, but introduction of the two genes carried on different plasmids conferred drug resistance. Thus, both EbrA and EbrB appear to be necessary for activity of the multidrug efflux pump. In known members of the SMR family, only one gene produces drug efflux. Thus, EbrAB is a novel SMR family multidrug efflux pump with two components.