Effect of new alleles of the histidine kinase gene ciaH on the activity of the response regulator CiaR in Streptococcus pneumoniae R6

Abstract

The two-component regulatory system CiaRH of Streptococcus pneumoniae affects b-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 b-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 b-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 CiaRdependent 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, b-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.

Comprehensive Identification of Single Nucleotide Polymorphisms Associated with Beta-lactam Resistance within Pneumococcal Mosaic Genes

“…In the Massachusetts data alone, we observed associations between resistance and ciaH , a histidine kinase sensor, and ciaR , its response regulator, consistent with previous studies reporting a large increase in resistance due to ciaH mutations. The mutations in the ciaH kinase sensor resulted in hyperactivation of the ciaR regulator, which in turn leads to increased beta-lactam resistance [1], [39]. Association signals from ftsL and gpsB genes were detected in both datasets.…”

Biological and Epidemiological Features of Antibiotic-Resistant Streptococcus pneumoniae in Pre- and Post-Conjugate Vaccine Eras: a United States Perspective

“…Alterations within the two-component sensor kinase CiaH have been found within ␤-lactam-resistant mutants selected in the laboratory and in nature (134). These mutations result in higher expression levels of genes upregulated by the transcriptional regulator CiaR, although the putative affected genes actually conferring ␤-lactam resistance are unknown.…”

Small regulatory RNAs from low-GC Gram-positive bacteria

“…A putative transcriptional regulator spr0159 and comC , the gene encoding the precursor of the competence stimulating peptide CSP 86 were the remaining csRNA targets. Especially the identification of the latter was intriguing, since CiaRH was known to act negatively on competence development 87 , 88 . Mutation of comC between the SD sequence and the start codon partially disrupting complementarity to the csRNAs greatly diminished csRNA-mediated repression of a translational fusion.…”

“…Mutations in the histidine kinase gene ciaH leading to a hyperactive CiaRH system 87 , 88 have been shown to increase β-lactam resistance. Without csRNAs, these CiaRH hyperactive strains are no longer resistant, but the target(s) involved in this phenotype has not yet been identified.…”