Department of Biological Sciences, University of Delaware, Newark, Delaware, USA.
Department of Biological Sciences, University of Delaware, Newark, Delaware, USA
Appl Environ Microbiol. 2020 May 5;86(10). doi: 10.1128/AEM.00120-20.
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 has biosynthesis pathways for the compatible solutes ectoine (encoded by ) and glycine betaine (encoded by ), four betaine-carnitine-choline transporters (encoded by to ), and a second ProU transporter (encoded by ). All of these systems are osmotically inducible with the exception of Previously, it was shown that CosR, a MarR-type regulator, was a direct repressor of in species. In this study, we investigated whether CosR has a broader role in the osmotic stress response. Expression analyses demonstrated that , , , , and are repressed in low salinity. Examination of an in-frame deletion mutant showed that expression of these systems is derepressed in the mutant at low salinity compared with the wild type. DNA binding assays demonstrated that purified CosR binds directly to the regulatory region of both biosynthesis systems and four transporters. In green fluorescent protein (GFP) reporter assays, we demonstrated that CosR directly represses transcription of , , and Similar to , we showed was directly activated by the quorum-sensing LuxR homolog OpaR, suggesting a conserved mechanism of regulation among species. Phylogenetic analysis demonstrated that CosR is ancestral to the family, and bioinformatics analysis showed widespread distribution among in general. Incidentally, in , , , and , an unrelated MarR-type regulator gene named was clustered with , 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. 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 family as well as numerous 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.
细菌通过从环境中摄取或利用可用前体物合成来积累称为相容性溶质的小有机化合物，以响应渗透压胁迫来维持细胞的膨压。嗜盐菌有合成相容性溶质 4-羟乙基哌嗪乙磺酸（由 编码）和甘氨酸甜菜碱（由 编码）、四种甜菜碱-肉碱-胆碱转运蛋白（由 编码至 ）和第二种 ProU 转运蛋白（由 编码）的生物合成途径。除了 之外，所有这些系统都是渗透诱导的。先前的研究表明，MarR 型调节剂 CosR 是 种中 的直接阻遏物。在这项研究中，我们研究了 CosR 是否在渗透压应激反应中具有更广泛的作用。表达分析表明，在低盐度下， 、 、 、 和 受到抑制。对无框移码突变体的检查表明，与野生型相比，该突变体在低盐度下这些系统的表达被解除抑制。DNA 结合测定表明，纯化的 CosR 直接结合到两个生物合成系统和四个转运蛋白的调控区。在绿色荧光蛋白（GFP）报告基因测定中，我们证明 CosR 直接抑制 、 、 和 的转录。与 相似，我们表明 由群体感应 LuxR 同源物 OpaR 直接激活，这表明在 种中存在保守的调节机制。系统发育分析表明，CosR 是 家族的祖先，并且生物信息学分析表明它在一般的 中广泛分布。顺便说一句，在 、 、 和 中，一个名为 的与 聚类的无关 MarR 型调节剂基因表明存在另一种新型 4-羟乙基哌嗪乙磺酸生物合成调节剂。总的来说，这些数据表明 CosR 是一种广泛存在于细菌中的渗透压应激反应的全局调节剂。可以通过生物合成和转运来积累相容性溶质，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性溶质，因此需要抑制生物合成和转运系统。然而，这种抑制的机制尚不清楚。在这项研究中，我们表明 CosR 在多个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 存在于 家族的所有成员以及众多 中。总的来说，这些数据表明 CosR 是一种广泛存在于细菌中的渗透压应激反应的全局调节剂，控制的系统比以前证明的要多得多。
