Mason Charlotte, Thompson Christina, Ouyang Zhiming
Department of Molecular Medicine, University of South Florida, Tampa, FL, USA.
Mol Microbiol. 2020 Jul;114(1):172-183. doi: 10.1111/mmi.14504. Epub 2020 Apr 14.
The RNA polymerase-binding protein DksA, together with the alarmone nucleotides (p)ppGpp, mediates the stringent response to nutrient starvation in Borrelia burgdorferi. To date, the contribution of DksA to B. burgdorferi infection remains unknown. We report here that DksA is essential for B. burgdorferi to infect a mammalian host. dksA expression was highly induced during infection. Moreover, a dksA-deficient mutant was incapable of infecting mice. The mutant displayed growth defects when cultured in vitro and resistance to osmotic pressure was markedly reduced. These phenotypes were fully restored to those of the wild type when dksA mutation was complemented. We further showed that DksA controlled the expression of virulence-associated lipoprotein OspC, likely via the central alternative sigma factor RpoS. Synthesis of RpoS was abolished in the dksA mutant, but rpoS transcription remained unaffected. Additionally, we found that the expression of clpX, clpA, clpP, and clpP2 was significantly increased in the mutant, suggesting that DksA may post-transcriptionally regulate rpoS expression via its effect on ClpXP and/or ClpAP proteases. These combined data demonstrate that DksA regulates B. burgdorferi virulence at least partially through its influence on RpoS and OspC. This study thus elucidates that, in addition to function as a stringent response regulator, DksA promotes the transcription and/or translation of genes contributing to B. burgdorferi infectivity.
RNA聚合酶结合蛋白DksA与警报素核苷酸（p）ppGpp一起介导伯氏疏螺旋体对营养饥饿的应急反应。迄今为止，DksA对伯氏疏螺旋体感染的作用尚不清楚。我们在此报告，DksA对伯氏疏螺旋体感染哺乳动物宿主至关重要。在感染过程中，dksA表达被高度诱导。此外，dksA缺陷型突变体无法感染小鼠。该突变体在体外培养时表现出生长缺陷，并且对渗透压的抗性明显降低。当dksA突变得到互补时，这些表型完全恢复为野生型。我们进一步表明，DksA可能通过中心替代sigma因子RpoS控制毒力相关脂蛋白OspC的表达。在dksA突变体中，RpoS的合成被消除，但rpoS转录不受影响。此外，我们发现突变体中clpX、clpA、clpP和clpP2的表达显著增加，这表明DksA可能通过其对ClpXP和/或ClpAP蛋白酶的作用在转录后调节rpoS表达。这些综合数据表明，DksA至少部分地通过其对RpoS和OspC的影响来调节伯氏疏螺旋体的毒力。因此，本研究阐明，除了作为应急反应调节因子发挥作用外，DksA还促进了有助于伯氏疏螺旋体感染性的基因的转录和/或翻译。
