Target evaluation of the non‐coding csRNAs reveals a link of the two‐component regulatory system CiaRH to competence control in Streptococcus pneumoniae R6

Abstract

SummaryThe two-component regulatory system CiaRH of Streptococcus pneumoniae controls 25 genes, five of which specify homologous small non-coding csRNAs (cia-dependent small RNAs). The csRNAs were predicted to act regulatory as base-pairing sRNAs, but their targets have not been identified. By csRNA gene inactivations we established that the major phenotypes associated with a hyperactive CiaRH system, enhanced β-lactam resistance and prevention of genetic competence, are dependent on the csRNAs. Computational target predictions and evaluations by translational fusions identified six genes to be under csRNA control: spr0081, spr0371, spr0159, spr0551, spr1097 and spr2043(comC). Measuring the effect of single csRNAs on three targets indicated that they acted additively. One of the targets, comC(spr2043), encoding the precursor of the competence stimulating pheromone CSP, constitutes a link of CiaRH to competence control. Partially disrupting predicted csRNAcomC complementarity led to strongly diminished repression by the csRNAs and to transformability in a strain with a hyperactive CiaRH. Thus, a hyperactive CiaRH system prevents competence development by csRNA-dependent post-transcriptional repression of CSP production. The csRNAs are also involved in competence regulation in the wild-type strain R6, but their activity is only apparent in the absence of the protease gene htrA, another CiaRH regulon member.

Mutation of the Thiol-Disulfide Oxidoreductase SdbA Activates the CiaRH Two-Component System, Leading to Bacteriocin Expression Shutdown in Streptococcus gordonii

“…Given that the components of the Com signaling system appeared to be functional, we reasoned that the lack of bacteriocin activity in the ⌬sdbA mutant might involve an indirect mechanism. In S. pneumoniae, the CiaRH two-component system represses both bacteriocin production and the Com signaling system (17,46), which was strikingly similar to the phenotype we observed in the ⌬sdbA mutant (26). Although the signals detected by the sensor protein CiaH are not known, certain conditions can increase the activity of the system (47-50), and we hypothesized that inactivation of sdbA might create a signal that increases CiaRH activity, leading to loss of bacteriocin production.…”

“…5A). The predicted csRNA binding sites were centered on the start codon and the ribosomal binding site and were almost identical to the experimentally verified csRNA binding sites on S. pneumoniae comC (46).…”

“…Upregulation of CiaRH inhibits the Com pathway in S. pneumoniae by inhibiting CSP production (46). The mechanism involves small noncoding RNAs that are regulated by CiaRH, which are thought to bind and to prevent translation of comC mRNA, thereby inhibiting CSP production (46).…”

“…Analysis of the csRNAs provided the first direct link between CiaRH signaling and genetic competence; comC was identified as a target of multiple csRNAs (46). The csRNAs are thought to work by binding to the Shine-Dalgarno sequence of complementary transcripts to prevent translation (46,60,61).…”

Addiction of Hypertransformable Pneumococcal Isolates to Natural Transformation for In Vivo Fitness and Virulence

“…Together, these genes are usually referred to as essential com genes (23). Competence is also regulated by the CiaRH two-component system through the serine protease HtrA (26,27) and noncoding small RNA (28,29). HtrA inhibits the activation of the competence system (27).…”