Department of Microbiology, University of Kaiserslautern, D-67663 Kaiserslautern, Germany.
Microbiology (Reading). 2011 Nov;157(Pt 11):3104-3112. doi: 10.1099/mic.0.053157-0. Epub 2011 Sep 8.
The two-component regulatory system CiaRH of Streptococcus pneumoniae affects β-lactam susceptibility, autolysis, bacteriocin production, competence development, host colonization and virulence. The system was discovered in a screen for S. pneumoniae R6 mutants resistant to the β-lactam antibiotic cefotaxime. A mutation in the histidine kinase gene ciaH led to this phenotype by enhancing CiaR-mediated gene expression. Additional mutations in ciaH have been described in other spontaneous β-lactam-resistant mutants of S. pneumoniae R6, but their influence on CiaR-mediated gene regulation has not been determined. Likewise, altered ciaH alleles are present in clinical S. pneumoniae isolates, none of which had been characterized. These novel ciaH variants were introduced into S. pneumoniae R6 to measure their ability to activate CiaR-dependent regulation. The ciaH alleles from spontaneous mutants obtained in the laboratory increased the activity of CiaR-dependent promoters between four- and 26-fold, while variants from clinical strains were less effective, with a threefold activation at most. Accordingly, phenotypes associated with a hyperactive CiaRH system, β-lactam resistance, and prevention of competence development, were far more pronounced in the laboratory mutants. Amino acid changes affecting CiaH function were positioned throughout the protein. Five of the most activating changes are located close to the conserved histidine and one in the extracytoplasmic sensor domain. The characterization of new alleles of ciaH expands the spectrum of CiaH variants, which may help to elucidate signal transduction of this important regulatory system. Our study also demonstrates that ciaH alleles overstimulating CiaR regulon expression are present in clinical isolates of S. pneumoniae.
肺炎链球菌的双组分调控系统 CiaRH 影响β-内酰胺类抗生素的敏感性、自溶、细菌素产生、感受态形成、宿主定植和毒力。该系统是在筛选肺炎链球菌 R6 突变体对β-内酰胺类抗生素头孢噻肟耐药性时发现的。组氨酸激酶基因 ciaH 的突变通过增强 CiaR 介导的基因表达导致了这种表型。在其他肺炎链球菌 R6 的自发β-内酰胺类耐药突变体中也描述了 ciaH 中的其他突变，但它们对 CiaR 介导的基因调控的影响尚未确定。同样，在临床分离的肺炎链球菌中也存在改变的 ciaH 等位基因，但它们都没有被表征。将这些新的 ciaH 变体引入肺炎链球菌 R6 中，以测量它们激活 CiaR 依赖性调控的能力。从实验室获得的自发突变体中的 ciaH 等位基因使 CiaR 依赖性启动子的活性增加了 4 到 26 倍，而来自临床株的变体的效果则较低，最大激活倍数为 3。因此，与 CiaRH 系统过度活跃、β-内酰胺类抗生素耐药性和阻止感受态形成相关的表型在实验室突变体中更为明显。影响 CiaH 功能的氨基酸变化遍布整个蛋白质。最具激活作用的五个变化位于保守的组氨酸附近，一个位于细胞外传感器结构域中。ciaH 新等位基因的表征扩展了 CiaH 变体的范围，这可能有助于阐明这个重要调控系统的信号转导。我们的研究还表明，在临床分离的肺炎链球菌中存在过度刺激 CiaR 调控子表达的 ciaH 等位基因。
