equisimilis and Streptococcus equi, are microbiologically similar to S. Groups C and G Streptococci, such as Streptococcus dysgalactiae subsp. pyogenes (Group A Streptococcus), an exclusively human pathogen, is involved in mild (pharyngitis, skin infections) to severe fatal invasive infections, such as necrotizing fasciitis and streptococcal toxic shock syndrome. pneumoniae is the main cause of community-acquired pneumonia, meningitis, and acute otitis media. The major species in human infections are Streptococcus pneumoniae, S. Although this genus includes beneficial species such as Streptococcus thermophilus, used in the food industry for the production of yogurt ( Blomqvist et al., 2006), streptococci are opportunistic pathogens, often involved in severe diseases in humans and farm animals. The Streptococcus genus is composed of chain-forming gram-positive bacteria including a large number of species (>100). Streptococcus Species Harboring a TCS Ciarh Finally, this review focuses on all csRNAs identified until now and their functions. It starts by highlighting the most important streptococcal species harboring a CiaRH and then analyzes the CiaRH TCS roles. This review concerns csRNAs identified in streptococci. Interestingly, it controls the expression of sRNAs called cia-dependent sRNAs (csRNAs) ( Halfmann et al., 2007). It is widespread among Streptococci but not found in another bacterial genus. The TCS CiaRH was identified to be involved in natural competence and general virulence ( Patenge et al., 2013). In Streptococci, many TCSs have been found. Although some of them are commensal, other are responsible for severe infections in humans ( Krzyściak et al., 2013). Streptococcal species infect humans and farm animals. To respond to environmental changes, bacteria must first sense these changes, and two-component regulatory systems (TCS) are known to perform this function ( Stock et al., 2000). This sRNA inhibits the translation of OmpF messenger RNA (mRNA) encoding the major membrane porin, OmpF ( Mizuno et al., 1984). In 1984, the first chromosomally encoded sRNA was discovered in Escherichia coli: MicF. All sRNAs are classified in several groups according to their location in the genome and their modes of action ( Storz et al., 2011). However, sRNAs, 50–500 nucleotides long molecules, are often involved in the regulation of several cellular pathways and allow bacteria to adapt and survive under stressful conditions. Interestingly, these sRNAs differ in length, structure, and mode of action ( Gottesman and Storz, 2011). A decade ago, the high number of sRNAs discovered in various bacterial species was surprising ( Brantl, 2009). Adaptation to the environment involves a complex regulatory network in which sRNAs play an essential role. The sRNAs were discovered in prokaryotes long before the first short interfering RNAs (siRNAs) and microRNAs (miRNAs) in eukaryotes. Finally, we give an overview of csRNAs and their functions in Streptococci with a focus on their importance in bacterial adaptation and virulence.ĭue to their importance in the regulation of gene expression, small non-coding regulatory RNAs (sRNAs) are present in all kingdoms of life. Then the role of CiaRH in streptococcal pathogenesis is discussed in the context of recent studies. In this review, we start by focusing on the Streptococcus species harboring a CiaRH TCS. In several streptococcal species, some sRNAs belong to the CiaRH regulon and are called csRNAs for cia-dependent sRNAs. The TCS CiaRH is highly conserved among this genus and crucial in bacterial survival under stressful conditions. Streptococci are opportunistic pathogens for humans and farm animals. It is followed by posttranscriptional regulations in which small regulatory RNAs (sRNAs) may affect RNA translation. A first line of control is transcriptional with regulators such as two-component systems (TCSs) that respond to physical and chemical perturbations. 2Centre Hospitalier Universitaire de Tours, Service de Bactériologie, Virologie, et Hygiène Hospitalière, Tours, Franceīacteria adapt to the different environments encountered by rapid and tightly controlled regulations involving complex networks.1Université de Tours, INRAE, ISP, Tours, France.Nancy Jabbour 1 and Marie-Frédérique Lartigue 1,2*
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