An Inventory of CiaR-Dependent Small Regulatory RNAs in Streptococci

Abstract

Bacteria adapt to the different environments encountered by rapid and tightly controlled regulations involving complex networks. A first line of control is transcriptional with regulators such as two-component systems (TCSs) that respond to physical and chemical perturbations. It is followed by posttranscriptional regulations in which small regulatory RNAs (sRNAs) may affect RNA translation. Streptococci are opportunistic pathogens for humans and farm animals. The TCS CiaRH is highly conserved among this genus and crucial in bacterial survival under stressful conditions. In several streptococcal species, some sRNAs belong to the CiaRH regulon and are called csRNAs for cia-dependent sRNAs. In this review, we start by focusing on the Streptococcus species harboring a CiaRH TCS. Then the role of CiaRH in streptococcal pathogenesis is discussed in the context of recent studies. Finally, we give an overview of csRNAs and their functions in Streptococci with a focus on their importance in bacterial adaptation and virulence.

Keywords: CiaRH; Streptococci; csRNAs; regulation; regulatory RNAs.

FIGURE 1

Regulation of csRNAs expression by TCS CiaRH after exposure of the cell to extracellular stimuli. First, the sensor CiaH detects extracellular stimuli such as pH variation and antibiotics exposure. CiaH transduces the signal to the regulator CiaR that interacts with promotor and allows csRNA expression. Then, csRNA interacts with target mRNA and allows or represses the translation. For example, in S. sanguinis, the csRNA1-1 interacts with the PilT mRNA and represses the translation of PilT protein inducing the reduction of biofilm formation. In S. pneumoniae, csRNA1 combined with csRNA2 and csRNA3 allows the repression of ComC translation, which reduces the natural competence of bacteria.

FIGURE 2

Alignments of csRNAs sequences by species by MultAlin. Nucleotides in red correspond to highly conserved sequences. Nucleotides in blue correspond to conserved sequences. Nucleotides in black correspond to non-conserved sequences.