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Diminished Redundancy of Outer Membrane Factor Proteins in Rhizobiales: A <i>nodT</i> Homolog Is Essential for Free-Living <i>Rhizobium etli</i>

2007; Volume: 13; Issue: 1-3 Linguagem: Inglês

10.1159/000103594

2673-1673

Armando Hernández-Mendoza, Noreide Nava, Olivia Santana, Cei Abreu‐Goodger, Anibal Tovar, Carmen Quinto,

Plant Pathogenic Bacteria Studies

<i>Rhizobium etli</i> is a gram-negative soil bacterium that induces nitrogen-fixing nodules on common bean roots <i>(Phaseolus vulgaris)</i>. <i>R. etli</i> encodes two genes homologous to <i>nodT </i>of <i>Rhizobium leguminosarum</i>. <i>nodTch</i> is chromosomal and forms an operon with new genes resembling a multi-drug efflux pump of the resistance-nodulation-cell division (RND) family. <i>nodTch</i> is the last gene of this operon and can also be independently transcribed; the gene product is located in the bacterial outer membrane. Cell survival requires <i>nodTch</i> under all conditions tested. A second <i>nodT</i> gene, <i>nodTpc</i>, is encoded by plasmid c; it is constitutively transcribed but does not complement the essential function encoded by <i>nodTch</i>. NodT proteins belong to the outer membrane efflux proteins of the TolC superfamily. The number of duplications in the <i>tolC</i> gene family positively correlates with genome size in gram-negative bacteria. Nonetheless, some α-proteobacteria, including <i>R. etli</i>, encode fewer outer membrane factor exporters than expected suggesting further roles in addition to detoxification.