Multiresistance genes of Rhizobium etli CFN42

Multidrug efflux pumps of bacteria are involved in the resistance to variou s antibiotics and toxic compounds. In Rhizobium etli, a mutualistic symbion t of Phaseolus vulgaris (bean), genes resembling multidrug efflux pump gene s were identified and designated rmrA and rmrB. rmrA was obtained after the screening of transposon-generated fusions that are inducible by bean-root released flavonoids, The predicted gene products of rmrAB shared significan t homology to membrane fusion and major facilitator proteins, respectively. Mutants of rmrA formed on average 40% less nodules in bean, while mutants of rmrA and rmrB had enhanced sensitivity to phytoalexins, flavonoids, and salicylic acid, compared with the wild-type strain. Multidrug resistance ge nes emrAB from Escherichia coli complemented an rmrA mutant from R, etli fo r resistance to high concentrations of naringenin.