The 4.5S RNA component of the signal recognition particle is required for group A Streptococcus virulence

Abstract

The signal recognition particle (SRP) is a ribonucleoprotein complex that targets proteins for secretion in a co-translational manner. While originally thought to be essential in all bacteria, recent data show that the SRP is dispensable in at least some streptococcal species. The SRP from the human pathogen group A Streptococcus (GAS, Streptococcus pyogenes) is predicted to be composed of protein Ffh and 4.5S RNA. Deletion of ffh alters the secretion of several GAS proteins, and leads to a severe reduction in virulence. Here, we report that mutation of the gene encoding 4.5S RNA results in phenotypes both similar to and distinct from that observed following ffh mutation. Similarities include a reduction in secretion of the haemolysin streptolysin O, and attenuation of virulence as assessed by a murine soft tissue infection model. Differences include a reduction in transcript levels for the genes encoding streptolysin O and NADglycohydrolase, and the reduced secretion of the SpeB protease. Several differences in transcript abundance between the parental and mutant strain were shown to be dependent on the sensorkinase-encoding gene covS. Using growth in human saliva as an ex vivo model of upper respiratory tract infection we identified that 4.5S RNA mutation leads to a 10-fold reduction in colony-forming units over time, consistent with the 4.5S RNA contributing to GAS growth and persistence during upper respiratory tract infections. Finally, we determined that the 4.5S RNA was essential for GAS to cause lethal infections in a murine bacteraemia model of infection. The data presented extend our knowledge of the contribution of the SRP to the virulence of an important Gram-positive pathogen.

Small RNAs in streptococci

“…In addition, the reduction in grab (encoding G-related alpha2-macroglobulin-binding protein G), slo and speB transcriptional expression in the sRNA mutant was shown to be dependent on the sensor kinase-encoding gene covS. 45 In MGAS2221, 4.5S RNA also influences positively the growth of S. pyogenes in human saliva, which led to the suggestion that the sRNA could contribute to growth and persistence of the pathogen during upper respiratory tract infections. 45 In this background, the sRNA was additionally required for S. pyogenes to cause lethal infections in murine models of bacteraemia.…”

“…1 and 2). Six sRNAs (FasX, Pel, RivX, 4.5S RNA, tracrRNA and crRNAs), 19,[42][43][44][45] were demonstrated to regulate virulence in S. pyogenes, among which, tracrRNA and crRNAs 19 were recently The numbers in plain letters indicate the total number of predicted srNAs whereas the numbers in bold letters indicate the number of validated srNAs. Please refer to the main text for all other abbreviations.…”

“…75 In a M1T1 serotype isolate (MGAS2221), 4.5S RNA is highly and constitutively transcribed during growth in nutrient-rich media and appears to have significant effects in pathogenic processes. 45 Compared to the parent strain, a 4.5S RNA mutant in MGAS2221 expressed lower levels of secreted streptolysin O (SLO), cysteine protease SpeB, streptococcal inhibitor of complement Sic and DNase 3. 45 Reduced levels of transcripts for the genes encoding SLO, superantigen SpeA and NADglycohydrolase were also observed.…”

“…45 Compared to the parent strain, a 4.5S RNA mutant in MGAS2221 expressed lower levels of secreted streptolysin O (SLO), cysteine protease SpeB, streptococcal inhibitor of complement Sic and DNase 3. 45 Reduced levels of transcripts for the genes encoding SLO, superantigen SpeA and NADglycohydrolase were also observed. In addition, the reduction in grab (encoding G-related alpha2-macroglobulin-binding protein G), slo and speB transcriptional expression in the sRNA mutant was shown to be dependent on the sensor kinase-encoding gene covS.…”

“…Both elements are dispensable for the species and have virulence functions. 45,75 In strain HSC5 (M14 serotype), Ffh controls positively the secretion of a distinct subset of virulence factors with cleavable signal sequences and influences virulence of the pathogen in necrotic myositis and subcutaneous models of infection. 75 In a M1T1 serotype isolate (MGAS2221), 4.5S RNA is highly and constitutively transcribed during growth in nutrient-rich media and appears to have significant effects in pathogenic processes.…”