Department of Molecular Biology, University of Wyoming, Laramie, Wyoming, USA.
Department of Molecular Biology, University of Wyoming, Laramie, Wyoming, USA
J Bacteriol. 2018 Feb 7;200(5). doi: 10.1128/JB.00457-17. Print 2018 Mar 1.
Elevated levels of the second messenger c-di-GMP suppress virulence in diverse pathogenic bacteria, yet mechanisms are poorly characterized. In the foodborne pathogen , high c-di-GMP levels inhibit mammalian cell invasion. Here, we show that invasion is impaired because of the decreased expression levels of internalin genes whose products are involved in invasion. We further show that at high c-di-GMP levels, the expression of the entire virulence regulon is suppressed, and so is the expression of the gene encoding the master activator of the virulence regulon. Analysis of mechanisms controlling expression pointed to the transcription factor CodY as a c-di-GMP-sensitive component. In high-c-di-GMP strains, gene expression is decreased, apparently due to the lower activity of CodY, which functions as an activator of transcription. We found that listerial CodY does not bind c-di-GMP and therefore investigated whether c-di-GMP levels affect two known cofactors of listerial CodY, branched-chain amino acids and GTP. Our manipulation of branched-chain amino acid levels did not perturb the c-di-GMP effect; however, our replacement of listerial CodY with the streptococcal CodY homolog, whose activity is GTP independent, abolished the c-di-GMP effect. The results of this study suggest that elevated c-di-GMP levels decrease the activity of the coordinator of metabolism and virulence, CodY, possibly via lower GTP levels, and that decreased CodY activity suppresses virulence by the decreased expression of the PrfA virulence regulon. is a pathogen causing listeriosis, a disease responsible for the highest mortality rate among foodborne diseases. Understanding how the virulence of this pathogen is regulated is important for developing treatments to decrease the frequency of listerial infections in susceptible populations. In this study, we describe the mechanism through which elevated levels of the second messenger c-di-GMP inhibit listerial invasion in mammalian cells. Inhibition is caused by the decreased activity of the transcription factor CodY that coordinates metabolism and virulence.
二信使 c-di-GMP 水平升高可抑制多种病原菌的毒力，但机制尚不清楚。在食源性病原体 中，高 c-di-GMP 水平可抑制哺乳动物细胞入侵。在这里，我们发现入侵受损是因为参与入侵的内毒素基因的表达水平降低。我们进一步表明，在高 c-di-GMP 水平下，整个毒力调节子的表达受到抑制，编码毒力调节子主激活子的 基因的表达也受到抑制。控制 基因表达的机制分析表明，转录因子 CodY 是 c-di-GMP 敏感的组成部分。在高 c-di-GMP 菌株中， 基因表达减少，显然是由于 CodY 活性降低，而 CodY 作为 转录的激活剂起作用。我们发现李斯特菌 CodY 不与 c-di-GMP 结合，因此研究了 c-di-GMP 水平是否影响李斯特菌 CodY 的两个已知辅因子，支链氨基酸和 GTP。我们对支链氨基酸水平的操纵并未扰乱 c-di-GMP 的作用；然而，我们用链球菌 CodY 同源物替换李斯特菌 CodY，其活性不依赖于 GTP，消除了 c-di-GMP 的作用。这项研究的结果表明，升高的 c-di-GMP 水平可能通过降低 GTP 水平降低代谢和毒力协调者 CodY 的活性，并且 CodY 活性降低通过降低 PrfA 毒力调节子的表达来抑制 毒力。是一种引起李斯特菌病的病原体，这是食源性疾病中死亡率最高的疾病。了解这种病原体的毒力如何受到调节对于开发减少易感人群中李斯特菌感染的频率的治疗方法非常重要。在这项研究中，我们描述了第二信使 c-di-GMP 升高抑制李斯特菌在哺乳动物细胞中入侵的机制。抑制是由转录因子 CodY 的活性降低引起的，CodY 协调代谢和毒力。
