Bacteria accumulate small, organic compounds, called compatible solutes, via uptake from the environment or biosynthesis from available precursors to maintain the turgor pressure of the cell in response to osmotic stress. The halophile Vibrio parahaemolyticus has biosynthesis pathways for the compatible solutes ectoine (ectABCasp_ect) and glycine betaine (betIBAproXWV), four betaine-carnitine-choline transporters (bcct1-bcct4) and a second ProU transporter (proVWX). All of these systems are osmotically inducible with the exception of bcct2. Previously, it was shown that CosR, a MarR-type regulator, was a direct repressor of ectABCasp_ect in Vibrio species. In this study, we investigated whether CosR has a broader role in the osmotic stress response. Expression analyses demonstrated that betIBAproXWV, bcct1, bcct3, bcct4 and proVWX are repressed in low salinity. Examination of an in-frame cosR deletion mutant showed expression of these systems is de-repressed in the mutant at low salinity compared to wild-type. DNA binding assays demonstrated that purified CosR binds directly to the regulatory region of both biosynthesis systems and four transporters. In Escherichia coli GFP reporter assays, we demonstrated that CosR directly represses transcription of betIBAproXWV, bcct3, and proVWX. Similar to V. harveyi, we showed betIBAproXWV was directly activated by the quorum sensing LuxR homolog OpaR, suggesting a conserved mechanism of regulation among Vibrio species. Phylogenetic analysis demonstrated that CosR is ancestral to the Vibrionaceae family and bioinformatics analysis showed widespread distribution among Gamma-Proteobacteria in general. Incidentally, in Aliivibrio fischeri, A. finisterrensis, A. sifiae and A. wodanis, an unrelated MarR-type regulator named ectR was clustered with ectABC-asp, which suggests the presence of another novel ectoine biosynthesis regulator. Overall, these data show that CosR is a global regulator of osmotic stress response that is widespread among bacteria.

IMPORTANCE Vibrio parahaemolyticus can accumulate compatible solutes via biosynthesis and transport, which allow the cell to survive in high salinity conditions. There is little need for compatible solutes under low salinity conditions, and biosynthesis and transporter systems need to be repressed. However, the mechanism(s) of this repression is not known. In this study, we showed that CosR played a major role in the regulation of multiple compatible solute systems. Phylogenetic analysis showed that CosR is present in all members of the Vibrionaceae family as well as numerous Gamma-Proteobacteria. Collectively, these data establish CosR as a global regulator of the osmotic stress response that is widespread in bacteria, controlling many more systems than previously demonstrated.

细菌会通过从环境中吸收或从可用的前体中进行生物合成来积累小的有机化合物，称为相容性溶质，以维持细胞对渗透压的膨胀压力。嗜盐弧菌副溶血性弧菌具有兼容的溶质ectoine（ectABCasp_ect）和甘氨酸甜菜碱（betIBAproXWV），四个甜菜碱-肉碱-胆碱转运蛋白（bcct1-bcct4）和第二个ProU转运蛋白（proVWX）的生物合成途径。除bcct2外，所有这些系统都是渗透诱导的。此前，已表明COSR，一个马尔型调节器，是直接阻遏ectABCasp_ect在弧菌种。在这项研究中，我们调查了CosR在渗透胁迫反应中是否具有更广泛的作用。表达分析表明，betIBAproXWV，bcct1，bcct3，bcct4和proVWX在低盐度下受到抑制。框内cosR缺失突变体的检测显示，与野生型相比，这些系统的表达在低盐度下在突变体中被抑制。DNA结合试验表明，纯化的CosR直接与生物合成系统和四个转运蛋白的调节区结合。在大肠杆菌GFP报告基因检测中，我们证明了CosR直接抑制betIBAproXWV的转录，bcct3和proVWX。与哈氏弧菌相似，我们显示betIBAproXWV被群体感应LuxR同源物OpaR直接激活，表明弧菌物种之间的保守调节机制。系统发育分析表明，CosR是弧菌科的祖先，而生物信息学分析表明，一般来说，γ-变形杆菌之间存在广泛的分布。顺便说一下，在Aliivibrio fischeri，A。finisterrensis，A。sifiae和A. wodanis中，一个不相关的名为RectR的MarR型调节子与ectABC -asp聚集在一起。，这表明存在另一种新颖的植物素生物合成调节剂。总体而言，这些数据表明，CosR是一种在细菌中广泛存在的渗透压反应的全球调节剂。

重要 副溶血性弧菌可以通过生物合成和运输来积累相容的溶质，从而使细胞能够在高盐度条件下存活。在低盐度条件下几乎不需要相容的溶质，因此需要抑制生物合成和转运系统。但是，这种抑制的机制是未知的。在这项研究中，我们表明CosR在多种相容性溶质系统的调节中起主要作用。系统发育分析表明，COSR是存在于所有成员弧菌家人以及众多的伽玛-变形菌。总的来说，这些数据使CosR成为细菌中普遍存在的渗透应激反应的全球调节者，控制着比以前证明的更多的系统。