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Multiresistance Genes of Rhizobium etli CFN42

May 2000 , Volume 13 , Number  5
Pages  572 - 577

Ramón González-Pasayo 1 , 2 and Esperanza Martínez-Romero 1

1Centro de Investigación sobre Fijación de Nitrógeno; 2Universidad Nacional Autónoma de México, Apartado Postal 565-A, Cuernavaca, Morelos, México

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Accepted 12 January 2000.

Multidrug efflux pumps of bacteria are involved in the resistance to various antibiotics and toxic compounds. In Rhizobium etli, a mutualistic symbiont of Phaseolus vulgaris (bean), genes resembling multidrug efflux pump genes 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 significant 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 genes emrAB from Escherichia coli complemented an rmrA mutant from R. etli for resistance to high concentrations of naringenin.

© 2000 The American Phytopathological Society