Kovacikova Gabriela, Lin Wei, Taylor Ronald K, Skorupski Karen
Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA
J Bacteriol. 2017 Mar 14;199(7). doi: 10.1128/JB.00762-16. Print 2017 Apr 1.
FadR is a master regulator of fatty acid (FA) metabolism that coordinates the pathways of FA degradation and biosynthesis in enteric bacteria. We show here that a Δ mutation in the El Tor biotype of prevents the expression of the virulence cascade by influencing both the transcription and the posttranslational regulation of the master virulence regulator ToxT. FadR is a transcriptional regulator that represses the expression of genes involved in FA degradation, activates the expression of genes involved in unsaturated FA (UFA) biosynthesis, and also activates the expression of two operons involved in saturated FA (SFA) biosynthesis. Since FadR does not bind directly to the promoter, we determined whether the regulation of any of its target genes indirectly influenced ToxT. This was accomplished by individually inserting a double point mutation into the FadR-binding site in the promoter of each target gene, thereby preventing their activation or repression. Although preventing FadR-mediated activation of , which encodes the enzyme that carries out the first step in UFA biosynthesis, did not significantly influence either the transcription or the translation of ToxT, it reduced its levels and prevented virulence gene expression. In the mutant strain unable to carry out FadR-mediated activation of , expressing ectopically restored the levels of ToxT and virulence gene expression. Taken together, the results presented here indicate that FadR influences the virulence cascade in the El Tor biotype by modulating the levels of ToxT via two different mechanisms. Fatty acids (FAs) play important roles in membrane lipid homeostasis and energy metabolism in all organisms. In , the causative agent of the acute intestinal disease cholera, they also influence virulence by binding into an N-terminal pocket of the master virulence regulator, ToxT, and modulating its activity. FadR is a transcription factor that coordinately controls the pathways of FA degradation and biosynthesis in enteric bacteria. This study identifies a new link between FA metabolism and virulence in the El Tor biotype by showing that FadR influences both the transcription and posttranslational regulation of the master virulence regulator ToxT by two distinct mechanisms.
FadR是脂肪酸（FA）代谢的主要调节因子，可协调肠道细菌中FA降解和生物合成的途径。我们在此表明，El Tor生物型中的Δ突变通过影响主要毒力调节因子ToxT的转录和翻译后调节，阻止了毒力级联反应的表达。FadR是一种转录调节因子，可抑制参与FA降解的基因的表达，激活参与不饱和FA（UFA）生物合成的基因的表达，还可激活参与饱和FA（SFA）生物合成的两个操纵子的表达。由于FadR不直接结合到启动子上，我们确定其任何靶基因的调节是否间接影响ToxT。这是通过在每个靶基因启动子的FadR结合位点中单独插入双点突变来实现的，从而阻止它们的激活或抑制。尽管阻止FadR介导的对编码在UFA生物合成中执行第一步的酶的激活，对ToxT的转录或翻译没有显著影响，但它降低了其水平并阻止了毒力基因的表达。在无法进行FadR介导的激活的突变菌株中，异位表达可恢复ToxT的水平和毒力基因的表达。综上所述，此处呈现的结果表明，FadR通过两种不同机制调节ToxT的水平，从而影响El Tor生物型中的毒力级联反应。脂肪酸（FAs）在所有生物体的膜脂稳态和能量代谢中发挥重要作用。在急性肠道疾病霍乱的病原体中，它们还通过结合到主要毒力调节因子ToxT的N端口袋中并调节其活性来影响毒力。FadR是一种转录因子，可协调控制肠道细菌中FA降解和生物合成的途径。这项研究通过表明FadR通过两种不同机制影响主要毒力调节因子ToxT的转录和翻译后调节，确定了FA代谢与El Tor生物型中毒力之间的新联系。
