Diverse Genetic Regulon of the Virulence-Associated Transcriptional Regulator MucR in Brucella abortus 2308

Abstract

ABSTRACTThe Ros-type regulator MucR is one of the few transcriptional regulators that have been linked to virulence inBrucella. Here, we show that aBrucella abortusin-framemucRdeletion strain exhibits a pronounced growth defect duringin vitrocultivation and, more importantly, that themucRmutant is attenuated in cultured macrophages and in mice. The genetic basis for the attenuation ofBrucella mucRmutants has not been defined previously, but in the present study the genes regulated by MucR inB. abortushave been elucidated using microarray analysis and real-time reverse transcription-PCR (RT-PCR). InB. abortus2308, MucR regulates a wide variety of genes whose products may function in establishing and maintaining cell envelope integrity, polysaccharide biosynthesis, iron homeostasis, genome plasticity, and transcriptional regulation. Particularly notable among the MucR-regulated genes identified isarsR6(nolR), which encodes a transcriptional regulator previously linked to virulence inBrucella melitensis16 M. Importantly, electrophoretic mobility shift assays (EMSAs) determined that a recombinant MucR protein binds directly to the promoter regions of several genes repressed by MucR (includingarsR6[nolR]), and inBrucella, as in other alphaproteobacteria, MucR binds to its own promoter to repress expression of the gene that encodes it. Overall, these studies have uncovered the diverse genetic regulon of MucR inBrucella, and in doing so this work has begun to define the MucR-controlled genetic circuitry whose misregulation contributes to the virulence defect ofBrucella mucRmutants.