Identification of csrR/csrS, a genetic locus that regulates hyaluronic acid capsule synthesis in group A Streptococcus

Abstract

SummaryThe hyaluronic acid capsule of group A Streptococcus (GAS) is an important virulence factor, but little is known about mechanisms that regulate capsule expression. Transposon Tn916 mutagenesis of the poorly encapsulated M-type 3 GAS strain DLS003 produced a transconjugant that exhibited a mucoid colony morphology, reflecting increased hyaluronic acid capsule production. Analysis of chromosomal DNA sequence immediately downstream of the transposon insertion identified two open reading frames, designated csrR and csrS, which exhibited sequence similarity to bacterial two-component regulatory systems. We constructed an in-frame deletion mutation within csrR, which encodes the putative response component. Replacement of the native csrR gene in the DLS003 chromosome with the mutant allele resulted in a sixfold increase in capsule production and a corresponding increase in transcription of the has operon, which contains the essential genes for hyaluronic acid synthesis. Increased capsule production by the csrR mutant strain was associated with enhanced resistance to complement-mediated opsonophagocytic killing in vitro and with a 500-fold increase in virulence in mice. These results establish CsrR as a negative regulator of hyaluronic acid capsule synthesis and suggest that it is part of a twocomponent regulatory system that influences capsule expression and virulence.

Two-component signal transduction systems in oral bacteria

“…The TCS was originally designated CsrRS (Csr: capsule synthesis regulator) [155,156] and then renamed CovRS Spy (cov; control of virulence) based on the demonstration that the system repressed multiple virulence genes, including streptokinase ( ska ), streptolysin S ( sagA ), and mitogenic factor ( speMF ) [157]. Later studies showed that CovRS Spy directly or indirectly regulates approximately 10–15% of the S. pyogenes genome [158,159].…”

“…The TCS CovRS Spy is atypical because of its repressor functions, although it also positively regulates some genes in its regulon. Deletion of covR Spy increases transcription of a panel of CovR Spy -repressed genes and also survival of S. pyogenes to opsonophagocytic killing by human PMNs in vitro [155,158]. …”

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

“…The changes in transcript abundance following 4.5S RNA mutation are the reverse of that observed following mutation of covS (control of virulence Sensor; also known as csrS), which encodes the membrane-spanning sensor kinase component of the CovR/S two-component system (Bernish & van de Rijn, 1999;Engleberg et al, 2001;Federle et al, 1999;Gryllos et al, 2008;Levin & Wessels, 1998;Trevino et al, 2009). To test whether the transcriptional changes that occur following 4.5S RNA mutation are dependent on a functional covS gene we created a covS/4.5S RNA double mutant strain and compared transcript levels relative to a covS single mutant strain (Fig.…”

Toward a Genome-Wide Systems Biology Analysis of Host-Pathogen Interactions in Group A Streptococcus

“…14,52,55,57,58 Genetic inactivation of this TCS produces a mutant strain that is hypervirulent in mice, has a mucoid colony phenotype associated with overexpression of hyaluronic acid capsule, and has increased resistance to in vitro killing by human PMNs. In addition, increased transcripts for proteins likely to promote survival and virulence, including streptokinase, streptolysin S, and a DNase, were identified in the isogenic mutant strain by conventional Northern blot analysis.…”

“…The microarray analysis confirmed and extended evidence that the CovR-CovS TCS enhances bacterial survival during disseminated host infections. 57,58 This study provided crucial insights into strategies used by a bacterial pathogen to thwart host defenses and to survive in human blood and suggested new vaccine and therapeutic strategies.…”