Bimodal Expression of the Salmonella Typhimurium spv Operon

Abstract

<p class="first" id="d723685e169">Passaris <i>et al.</i> show that the well-studied spv virulence operon of <i>Salmonella</i> Typhimurium displays a bimodal expression pattern. Using quantitative single-cell fluorescence microscopy, they demonstrate that this expression pattern originates in the bimodal expression... </p><p class="first" id="d723685e178">The well-studied <i>spv</i> operon of <i>Salmonella</i> <i>typhimurium</i> is important for causing full virulence in mice and both the regulation and function of the Spv proteins have been characterized extensively over the past several decades. Using quantitative single-cell fluorescence microscopy, we demonstrate the <i>spv</i> regulon to display a bimodal expression pattern that originates in the bimodal expression of the SpvR activator. The <i>spv</i> expression pattern is influenced by growth conditions and the specific <i>S</i>. <i>typhimurium</i> strain used, but does not require <i>Salmonella</i>-specific virulence regulators. By monitoring real-time promoter kinetics, we reveal that SpvA has the ability to impart negative feedback on <i>spvABCD</i> expression without affecting <i>spvR</i> expression. Together, our data suggest that the SpvA protein counteracts the positive feedback loop imposed by SpvR, and could thus be responsible for dampening <i>spvABCD</i> expression and coordinating virulence protein production in time. The results presented here yield new insights in the intriguing regulation of the <i>spv</i> operon and adds this operon to the growing list of virulence factors exhibiting marked expression heterogeneity in <i>S</i>. <i>typhimurium</i>. </p>