Levin J C, Wessels M R
Channing Laboratory, Brigham and Women's Hospital, Boston, MA, USA.
Mol Microbiol. 1998 Oct;30(1):209-19. doi: 10.1046/j.1365-2958.1998.01057.x.
The hyaluronic acid capsule of group A Streptococcus (GAS) is an important virulence factor, but little is known about mechanisms that regulate capsule expression. Transposon Tn916 mutagenesis of the poorly encapsulated M-type 3 GAS strain DLS003 produced a transconjugant that exhibited a mucoid colony morphology, reflecting increased hyaluronic acid capsule production. Analysis of chromosomal DNA sequence immediately downstream of the transposon insertion identified two open reading frames, designated csrR and csrS, which exhibited sequence similarity to bacterial two-component regulatory systems. We constructed an in-frame deletion mutation within csrR, which encodes the putative response component. Replacement of the native csrR gene in the DLS003 chromosome with the mutant allele resulted in a sixfold increase in capsule production and a corresponding increase in transcription of the has operon, which contains the essential genes for hyaluronic acid synthesis. Increased capsule production by the csrR mutant strain was associated with enhanced resistance to complement-mediated opsonophagocytic killing in vitro and with a 500-fold increase in virulence in mice. These results establish CsrR as a negative regulator of hyaluronic acid capsule synthesis and suggest that it is part of a two-component regulatory system that influences capsule expression and virulence.
A 群链球菌（GAS）的透明质酸荚膜是一种重要的毒力因子，但关于调节荚膜表达的机制却知之甚少。对荚膜形成较差的 M 型 3 GAS 菌株 DLS003 进行转座子 Tn916 诱变，产生了一个表现出黏液样菌落形态的转接合子，这反映出透明质酸荚膜产量增加。对转座子插入位点下游紧邻的染色体 DNA 序列进行分析，鉴定出两个开放阅读框，分别命名为 csrR 和 csrS，它们与细菌双组分调节系统具有序列相似性。我们在编码假定应答组分的 csrR 内构建了一个框内缺失突变。用突变等位基因替换 DLS003 染色体上的天然 csrR 基因，导致荚膜产量增加了六倍，并且包含透明质酸合成必需基因的 has 操纵子的转录相应增加。csrR 突变株荚膜产量的增加与体外对补体介导的调理吞噬杀伤作用的抗性增强以及小鼠毒力增加 500 倍有关。这些结果确立了 CsrR 作为透明质酸荚膜合成的负调节因子，并表明它是影响荚膜表达和毒力的双组分调节系统的一部分。
