Identification of Rgg-regulated exoproteins of Streptococcus pyogenes

RopB-regulated SpeB cysteine protease degrades extracellular vesicles-associated streptolysin O and bacterial proteins from group A Streptococcus

Extracellular vesicles (EVs) can be released from gram-positive bacteria and would participate in the delivery of bacterial toxins. Streptococcus pyogenes (group A Streptococcus, GAS) is one of the most common pathogens of monomicrobial necrotizing fasciitis. Spontaneous inactivating mutation in the CovR/CovS two-component regulatory system is related to the increase of EVs production via an unknown mechanism. This study aimed to investigate whether the CovR/CovS-regulated RopB, the transcriptional regulator of GAS exoproteins, would participate in regulating EVs production. Results showed that the size, morphology, and number of EVs released from the wild-type strain and the ropB mutant were similar, suggesting RopB is not involved in controlling EVs production. Nonetheless, RopB-regulated SpeB protease degrades streptolysin O and bacterial proteins in EVs. Although SpeB has crucial roles in modulating protein composition in EVs, the SpeB-positive EVs failed to trigger HaCaT keratinocytes pyroptosis, suggesting that EVs did not deliver SpeB into keratinocytes or the amount of SpeB in EVs was not sufficient to trigger cell pyroptosis. Finally, we identified that EV-associated enolase was resistant to SpeB degradation, and therefore could be utilized as the internal control protein for verifying SLO degradation. This study revealed that RopB would participate in modulating protein composition in EVs via SpeB-dependent protein degradation and suggested that enolase is a potential internal marker for studying GAS EVs.

StkP- and PhpP-Mediated Posttranslational Modifications Modulate the S. pneumoniae Metabolism, Polysaccharide Capsule, and Virulence

Pneumococcal Ser/Thr kinase (StkP) and its cognate phosphatase (PhpP) play a crucial role in bacterial cytokinesis. However, their individual and reciprocal metabolic and virulence regulation-related functions have yet to be adequately investigated in encapsulated pneumococci. Here, we demonstrate that the encapsulated pneumococcal strain D39-derived D39ΔPhpP and D39ΔStkP mutants displayed differential cell division defects and growth patterns when grown in chemically defined media supplemented with glucose or nonglucose sugars as the sole carbon source. Microscopic and biochemical analyses supported by RNA-seq-based global transcriptomic analyses of these mutants revealed significantly down- and upregulated polysaccharide capsule formation and cps2 genes in D39ΔPhpP and D39ΔStkP mutants, respectively. While StkP and PhpP individually regulated several unique genes, they also participated in sharing the regulation of the same set of differentially regulated genes. Cps2 genes were reciprocally regulated in part by the StkP/PhpP-mediated reversible phosphorylation but independent of the MapZ-regulated cell division process. StkP-mediated dose-dependent phosphorylation of CcpA proportionately inhibited CcpA-binding to Pcps2A, supporting increased cps2 gene expression and capsule formation in D39ΔStkP. While the attenuation of the D39ΔPhpP mutant in two mouse infection models corroborated with several downregulated capsules-, virulence-, and phosphotransferase systems (PTS)-related genes, the D39ΔStkP mutant with increased amounts of polysaccharide capsules displayed significantly decreased virulence in mice compared to the D39 wild-type, but more virulence compared to D39ΔPhpP. NanoString technology-based inflammation-related gene expression and Meso Scale Discovery-based multiplex chemokine analysis of human lung cells cocultured with these mutants confirmed their distinct virulence phenotypes. StkP and PhpP may, therefore, serve as critical therapeutic targets.

The Proteomic and Transcriptomic Landscapes Altered by Rgg2/3 Activity in Streptococcus pyogenes

Streptococcus pyogenes, otherwise known as Group A Streptococcus (GAS), is an important and highly adaptable human pathogen with the ability to cause both superficial and severe diseases. Understanding how S. pyogenes senses and responds to its environment will likely aid in determining how it causes a breadth of diseases. One regulatory network involved in GAS's ability to sense and respond to the changing environment is the Rgg2/3 quorum sensing (QS) system, which responds to metal and carbohydrate availability and regulates changes to the bacterial surface. To better understand the impact of Rgg2/3 QS on S. pyogenes physiology, we performed RNA-seq and tandem mass tag (TMT)-LC-MS/MS analysis on cells in which this system was induced with short hydrophobic peptide (SHP) pheromone or disrupted. Primary findings confirmed that pheromone stimulation in wild-type cultures is limited to the induction of operons whose promoters contain previously determined Rgg2/3 binding sequences. However, a deletion mutant of rgg3, a strain that endogenously produces elevated amounts of pheromone, led to extended alterations of the transcriptome and proteome, ostensibly by stress-induced pathways. Under such exaggerated pheromone conditions, a connection was identified between Rgg2/3 and the stringent response. Mutation of relA, the bifunctional guanosine tetra- and penta-phosphate nucleoside synthetase/hydrolase, and alarmone synthase genes sasA and sasB, impacted culture doubling times and disabled induction of Rgg2/3 in response to mannose, while manipulation of Rgg2/3 signaling modestly altered nucleotide levels. Our findings indicate that excessive pheromone production or exposure places stress on GAS resulting in an indirect altered proteome and transcriptome beyond primary pheromone signaling. IMPORTANCE Streptococcus pyogenes causes several important human diseases. This study evaluates how the induction or disruption of a cell-cell communication system alters S. pyogenes's gene expression and, in extreme conditions, its physiology. Using transcriptomic and proteomic approaches, the results define the pheromone-dependent regulon of the Rgg2/3 quorum sensing system. In addition, we find that excessive pheromone stimulation, generated by genetic disruption of the Rgg2/3 system, leads to stress responses that are associated with the stringent response. Disruption of stringent response affects the ability of the cell-cell communication system to respond under normally inducing conditions. These findings assist in the determination of how S. pyogenes is impacted by and responds to nontraditional sources of stress.

Phosphorylation at the D53 but Not the T65 Residue of CovR Determines the Repression of rgg and speB Transcription in emm1- and emm49-Type Group A Streptococci

CovR/CovS is a two-component regulatory system in group A Streptococcus and primarily acts as a transcriptional repressor. The D53 residue of CovR (CovR_D53) is phosphorylated by the sensor kinase CovS, and the phosphorylated CovR_D53 protein binds to the intergenic region of rgg-speB to inhibit speB transcription. Nonetheless, the transcription of rgg and speB is suppressed in covS mutants. The T65 residue of CovR is phosphorylated in a CovS-independent manner, and phosphorylation at the D53 and T65 residues of CovR is mutually exclusive. Therefore, how phosphorylation at the D53 and T65 residues of CovR contributes to the regulation of rgg and speB expression was elucidated. The transcription of rgg and speB was suppressed in the strain that cannot phosphorylate the D53 residue of CovR (CovR_D53A mutant) but restored to levels similar to those of the wild-type strain in the CovR_T65A mutant. Nonetheless, inactivation of the T65 residue phosphorylation in the CovR_D53A mutant cannot derepress the rgg and speB transcription, indicating that phosphorylation at the T65 residue of CovR is not required for repressing rgg and speB transcription. Furthermore, trans complementation of the CovR_D53A protein in the strain that expresses the phosphorylated CovR_D53 resulted in the repression of rgg and speB transcription. Unlike the direct binding of the phosphorylated CovR_D53 protein and its inhibition of speB transcription demonstrated previously, the present study showed that inactivation of phosphorylation at the D53 residue of CovR contributes dominantly in suppressing rgg and speB transcription.IMPORTANCE CovR/CovS is a two-component regulatory system in group A Streptococcus (GAS). The D53 residue of CovR is phosphorylated by CovS, and the phosphorylated CovR_D53 binds to the rgg-speB intergenic region and acts as the transcriptional repressor. Nonetheless, the transcription of rgg and Rgg-controlled speB is upregulated in the covR mutant but inhibited in the covS mutant. The present study showed that nonphosphorylated CovR_D53 protein inhibits rgg and speB transcription in the presence of the phosphorylated CovR_D53 in vivo, indicating that nonphosphorylated CovR_D53 has a dominant role in suppressing rgg transcription. These results reveal the roles of nonphosphorylated CovR_D53 in regulating rgg transcription, which could contribute significantly to invasive phenotypes of covS mutants.

Paediatric obstructive sleep apnoea syndrome (OSAS) is associated with tonsil colonisation by Streptococcus pyogenes

The involvement of pathogenic bacteria in obstructive sleep apnoea syndrome (OSAS) has yet to be elucidated. We investigated the possible role of group A streptococcus (GAS) in OSAS pathogenesis. In 40 tonsillectomized patients affected by OSAS and 80 healthy controls, significant (p < 0.0001) association of GAS with paediatric OSAS was found. Supernatant from streptolysin O (SLO)-producing GAS induced production of cysteinyl leukotrienes (CysLTs) in tonsil mononuclear cells (TMCs). CysLTs-treated TMCs showed significant (p < 0.05) proliferation of CD4+ T, CD19+ and CD19+CD27+CD38+ B lymphocytes. We discovered a SLO-dependent activation of CysLTs production through a pathway involving TOLL-like receptor 4 (TLR4), TIR-domain-containing adapter-inducing interferon-β (TRIF), Myeloid differentiation primary response gene 88 (MyD88), and p38 MAP Kinase. In conclusion, we hypothesise that GAS may contribute to paediatric tonsillar hyperplasia through CysLTs production induced by SLO, and this might explain its association with OSAS.

Mechanisms of group A Streptococcus resistance to reactive oxygen species

Streptococcus pyogenes, also known as group A Streptococcus (GAS), is an exclusively human Gram-positive bacterial pathogen ranked among the ‘top 10’ causes of infection-related deaths worldwide. GAS commonly causes benign and self-limiting epithelial infections (pharyngitis and impetigo), and less frequent severe invasive diseases (bacteremia, toxic shock syndrome and necrotizing fasciitis). Annually, GAS causes 700 million infections, including 1.8 million invasive infections with a mortality rate of 25%. In order to establish an infection, GAS must counteract the oxidative stress conditions generated by the release of reactive oxygen species (ROS) at the infection site by host immune cells such as neutrophils and monocytes. ROS are the highly reactive and toxic byproducts of oxygen metabolism, including hydrogen peroxide (H₂O₂), superoxide anion (O₂•⁻), hydroxyl radicals (OH•) and singlet oxygen (O₂*), which can damage bacterial nucleic acids, proteins and cell membranes. This review summarizes the enzymatic and regulatory mechanisms utilized by GAS to thwart ROS and survive under conditions of oxidative stress.

This review discusses the mechanisms utilized by the bacterial pathogen group A Streptococcus to detoxify reactive oxygen species and survive in the human host under conditions of oxidative stress.

Quorum sensing in group A Streptococcus

Quorum sensing (QS) is a widespread phenomenon in the microbial world that has important implications in the coordination of population-wide responses in several bacterial pathogens. In Group A Streptococcus (GAS), many questions surrounding QS systems remain to be solved pertaining to their function and their contribution to the GAS lifestyle in the host. The QS systems of GAS described to date can be categorized into four groups: regulator gene of glucosyltransferase (Rgg), Sil, lantibiotic systems, and LuxS/AI-2. The Rgg family of proteins, a conserved group of transcription factors that modify their activity in response to signaling peptides, has been shown to regulate genes involved in virulence, biofilm formation and competence. The sil locus, whose expression is regulated by the activity of signaling peptides and a putative two-component system (TCS), has been implicated on regulating genes involved with invasive disease in GAS isolates. Lantibiotic regulatory systems are involved in the production of bacteriocins and their autoregulation, and some of these genes have been shown to target both bacterial organisms as well as processes of survival inside the infected host. Finally AI-2 (dihydroxy pentanedione, DPD), synthesized by the LuxS enzyme in several bacteria including GAS, has been proposed to be a universal bacterial communication molecule. In this review we discuss the mechanisms of these four systems, the putative functions of their targets, and pose critical questions for future studies.

Response of Different Antibiotic Resistant Group of Streptococcus pyogenes to Environmental Stresses

Streptococcus species is considered as an important pathogen for human and animals. The antibiotic resistance mechanism in this species is continuously increased. On the other side, the tolerance of environmental stresses play an effective role in the severity of many streptococcal causative disease. In this study we assayed survey on the causative agents of pharyngitis and tonsillitis patients. The predominant causative strain was Streptococcus pyogenes with 93 % isolating ratio frequency. The other pathogenic species were S. agalactia 5.3 % and S. pneumonia 1.7 %. According to the antibiotic resistant test the S. pyogenes isolates were classified into six different groups. A selected strain from each antibiotic resistant group was tested for tolerance of a restrictive environmental factors. The variations of the environmental niches of isolates were in consistence with their antibiotic resistant variation.

Natural variation in the promoter of the gene encoding the Mga regulator alters host-pathogen interactions in group a Streptococcus carrier strains

Humans commonly carry pathogenic bacteria asymptomatically, but the molecular factors underlying microbial asymptomatic carriage are poorly understood. We previously reported that two epidemiologically unassociated serotype M3 group A Streptococcus (GAS) carrier strains had an identical 12-bp deletion in the promoter of the gene encoding Mga, a global positive gene regulator. Herein, we report on studies designed to test the hypothesis that the identified 12-bp deletion in the mga promoter alters GAS virulence, thereby potentially contributing to the asymptomatic carrier phenotype. Using allelic exchange, we introduced the variant promoter into a serotype M3 invasive strain and the wild-type promoter into an asymptomatic carrier strain. Compared to strains with the wild-type mga promoter, we discovered that strains containing the promoter with the 12-bp deletion produced significantly fewer mga and Mga-regulated gene transcripts. Consistent with decreased mga transcripts, strains containing the variant mga promoter were also significantly less virulent in in vivo and ex vivo models of GAS disease. Further, we provide evidence that the pleiotropic regulator protein CodY binds to the mga promoter and that the 12-bp deletion in the mga promoter reduces CodY-mediated mga transcription. We conclude that the naturally occurring 12-bp deletion in the mga promoter significantly alters the pathogen-host interaction of these asymptomatic carrier strains. Our findings provide new insight into the molecular basis of the carrier state of an important human pathogen.

Enterococcal Rgg-like regulator ElrR activates expression of the elrA operon

The Enterococcus faecalis leucine-rich protein ElrA promotes virulence by stimulating bacterial persistence in macrophages and production of the interleukin-6 (IL-6) cytokine. The ElrA protein is encoded within an operon that is poorly expressed under laboratory conditions but induced in vivo. In this study, we identify ef2687 (renamed elrR), which encodes a member of the Rgg (regulator gene for glucosyltransferase) family of putative regulatory proteins. Using quantitative reverse transcription-PCR, translational lacZ fusions, and electrophoretic mobility shift assays, we demonstrate that ElrR positively regulates expression of elrA. These results correlate with the attenuated virulence of the ΔelrR strain in a mouse peritonitis model. Virulence of simple and double elrR and elrA deletion mutants also suggests a remaining ElrR-independent expression of elrA in vivo and additional virulence-related genes controlled by ElrR.

Transcriptional regulation of a bacteriophage encoded extracellular DNase (Spd-3) by Rgg in Streptococcus pyogenes

The Streptococcus pyogenes transcriptional regulator Rgg controls the expression of virulence-associated genes encoded both within the core genome and within horizontally transmissible DNA such as temperate bacteriophage. Previously, we showed that Rgg binds to the non-coding DNA upstream of the bacteriophage gene encoding an extracellular DNase Spd-3. In the current study, we further characterized Rgg-mediated regulation of spd-3 expression. Two spd-3 transcripts were identified by northern blotting. The 5′ ends were 27 and 594 nucleotides upstream of the start codon as determined with primer extension analysis and 5′ RACE (rapid amplification of c-DNA ends), respectively. Results obtained with gel shift assays showed that purified Rgg bound specifically to non-coding DNA containing the promoters of both transcripts. Transcriptional fusion analyses confirmed the presence of Rgg-repressible promoters within these DNA regions. In addition, repression was associated with direct DNA binding by Rgg as determined with chromatin immunoprecipitation (ChIP) coupled with quantitative PCR (qPCR). The results show that the chromosomally encoded transcriptional regulator, Rgg, directly represses both bacteriophage promoters controlling the expression of Spd-3. The results provide new information regarding the regulation of prophage encoded virulence factors of S. pyogenes and highlight the complex evolutionary history of S. pyogenes and temperate bacteriophage.

Induction of the Yersinia pestis PhoP-PhoQ regulatory system in the flea and its role in producing a transmissible infection

Transmission of Yersinia pestis is greatly enhanced after it forms a bacterial biofilm in the foregut of the flea vector that interferes with normal blood feeding. Here we report that the ability to produce a normal foregut-blocking infection depends on induction of the Y. pestis PhoP-PhoQ two-component regulatory system in the flea. Y. pestis phoP-negative mutants achieved normal infection rates and bacterial loads in the flea midgut but produced a less cohesive biofilm both in vitro and in the flea and had a greatly reduced ability to localize to and block the flea foregut. Thus, not only is the PhoP-PhoQ system induced in the flea gut environment, but also this induction is required to produce a normal transmissible infection. The altered biofilm phenotype in the flea was not due to lack of PhoPQ-dependent or PmrAB-dependent addition of aminoarabinose to the Y. pestis lipid A, because an aminoarabinose-deficient mutant that is highly sensitive to cationic antimicrobial peptides had a normal phenotype in the flea digestive tract. In addition to enhancing transmissibility, induction of the PhoP-PhoQ system in the arthropod vector prior to transmission may preadapt Y. pestis to resist the initial encounter with the mammalian innate immune response.

Human pathogenic streptococcal proteomics and vaccine development

Gram-positive streptococci are non-motile, chain-forming bacteria commonly found in the normal oral and bowel flora of warm-blooded animals. Over the past decade, a proteomic approach combining 2-DE and MS has been used to systematically map the cellular, surface-associated and secreted proteins of human pathogenic streptococcal species. The public availability of complete streptococcal genomic sequences and the amalgamation of proteomic, genomic and bioinformatic technologies have recently facilitated the identification of novel streptococcal vaccine candidate antigens and therapeutic agents. The objective of this review is to examine the constituents of the streptococcal cell wall and secreted proteome, the mechanisms of transport of surface and secreted proteins, and describe the current methodologies employed for the identification of novel surface-displayed proteins and potential vaccine antigens.

Growth phase-dependent modulation of Rgg binding specificity in Streptococcus pyogenes

Streptococcus pyogenes Rgg is a transcriptional regulator that interacts with the cofactor LacD.1 to control growth phase-dependent expression of genes, including speB, which encodes a secreted cysteine protease. LacD.1 is thought to interact with Rgg when glycolytic intermediates are abundant in a manner that prevents Rgg-mediated activation of speB expression via binding to the promoter region. When the intermediates diminish, LacD.1 dissociates from Rgg and binds to the speB promoter to activate expression. The purpose of this study was to determine if Rgg bound to chromatin during the exponential phase of growth and, if so, to identify the binding sites. Rgg bound to 62 chromosomal sites, as determined by chromatin immunoprecipitation coupled with DNA microarrays. Thirty-eight were within noncoding DNA, including sites upstream of the genes encoding the M protein (M49), serum opacity factor (SOF), fibronectin-binding protein (SfbX49), and a prophage-encoded superantigen, SpeH. Each of these sites contained a promoter that was regulated by Rgg, as determined with transcriptional fusion assays. Purified Rgg also bound to the promoter regions of emm49, sof, and sfbX49 in vitro. Results obtained with a lacD.1 mutant showed that both LacD.1 and Rgg were necessary for the repression of emm49, sof, sfbX49, and speH expression. Overall, the results indicated that the DNA binding specificity of Rgg is responsive to environmental changes in a LacD.1-dependent manner and that Rgg and LacD.1 directly control virulence gene expression in the exponential phase of growth.

Polymorphisms in regulator of protease B (RopB) alter disease phenotype and strain virulence of serotype M3 group A Streptococcus

Whole-genome sequencing of serotype M3 group A streptococci (GAS) from oropharyngeal and invasive infections in Ontario recently showed that the gene encoding regulator of protease B (RopB) is highly polymorphic in this population. To test the hypothesis that ropB is under diversifying selective pressure among all serotype M3 GAS strains, we sequenced this gene in 1178 strains collected from different infection types, geographic regions, and time periods. The results confirmed our hypothesis and discovered a significant association between mutant ropB alleles, decreased activity of its major regulatory target SpeB, and pharyngitis. Additionally, isoallelic strains with ropB polymorphisms were significantly less virulent in a mouse model of necrotizing fasciitis. These studies provide a model strategy for applying whole-genome sequencing followed by deep single-gene sequencing to generate new insight to the rapid evolution and virulence regulation of human pathogens.

The rgg0182 gene encodes a transcriptional regulator required for the full Streptococcus thermophilus LMG18311 thermal adaptation

Background

Streptococcus thermophilus is an important starter strain for the production of yogurt and cheeses. The analysis of sequenced genomes of four strains of S. thermophilus indicates that they contain several genes of the rgg familly potentially encoding transcriptional regulators. Some of the Rgg proteins are known to be involved in bacterial stress adaptation.

Results

In this study, we demonstrated that Streptococcus thermophilus thermal stress adaptation required the rgg₀₁₈₂ gene which transcription depends on the culture medium and the growth temperature. This gene encoded a protein showing similarity with members of the Rgg family transcriptional regulator. Our data confirmed that Rgg₀₁₈₂ is a transcriptional regulator controlling the expression of its neighboring genes as well as chaperones and proteases encoding genes. Therefore, analysis of a Δrgg₀₁₈₂ mutant revealed that this protein played a role in the heat shock adaptation of Streptococcus thermophilus LMG18311.

Conclusions

These data showed the importance of the Rgg₀₁₈₂ transcriptional regulator on the survival of S. thermophilus during dairy processes and more specifically during changes in temperature.

Evolution of diversity in epidemics revealed by analysis of the human bacterial pathogen group A Streptococcus

Advancements in high-throughput, high-volume data generating techniques increasingly present us with opportunities to probe new areas of biology. In this work we assessed the extent to which four closely related and genetically representative strains of group A Streptococcus causing epidemic disease have differentiated from one another. Comparative genome sequencing, expression microarray analysis, and proteomic studies were used in parallel to assess strain variation. The extent of phenotypic differentiation was unexpectedly large. We found significant associations between genetic polymorphisms and alterations in gene expression allowing us to estimate the frequency with which specific types of polymorphisms alter gene transcription. We identified polymorphisms in the gene (ropB) encoding the RopB regulator that associate with altered transcription of speB and production of the SpeB protein, a critical secreted protease virulence factor. Although these four epidemic strains are closely related, a key discovery is that accumulation of modest genetic changes has rapidly resulted in significant strain phenotypic differentiation, including the extracellular proteome that contains multiple virulence factors. These data provide enhanced understanding of genetic events resulting in strain variation in bacterial epidemics.

Identification of Rgg binding sites in the Streptococcus pyogenes chromosome

Streptococcus pyogenes Rgg is a regulatory protein that controls the transcription of 588 genes in strain NZ131 during the post-exponential phase of growth, including the virulence-associated genes encoding the extracellular SpeB protease, pullulanase A (PulA), and two extracellular nucleases (SdaB and Spd-3). Rgg binds to DNA proximally to the speB promoter (PspeB) to activate transcription; however, it is not known if Rgg binds to the promoters of other genes to influence expression, or if the perturbation of other global regulons accounts for the genome-wide changes in expression associated with the mutant. To address this issue, chromatin immunoprecipitation followed by DNA microarray analysis (ChIP-chip) was used to identify the DNA binding sites of Rgg. Rgg bound to 65 sites in the chromosome. Thirty-five were within noncoding DNA, and 43% of these were adjacent to genes previously identified as regulated by Rgg. Electrophoretic mobility shift assays were used to assess the binding of Rgg to a subset of sites bound in vivo, including the noncoding DNA upstream of speB, the genes encoding PulA, Spd-3, and a transcriptional regulator (SPY49_1113), and prophage-associated genes encoding a putative integrase (SPY49_0746) and a surface antigen (SPY49_0396). Rgg bound to all target DNAs in vitro, consistent with the in vivo results. Finally, analyses with a transcriptional reporter system showed that the DNA bound by Rgg contained an active promoter that was regulated by Rgg. Overall, the results indicate that Rgg binds specifically to multiple sites in the chromosome, including prophage DNA, to influence gene expression.

Niche-specific contribution to streptococcal virulence of a MalR-regulated carbohydrate binding protein

Low G+C Gram-positive bacteria typically contain multiple LacI/GalR regulator family members, which often have highly similar amino-terminal DNA binding domains, suggesting significant overlap in target DNA sequences. The LacI/GalR family regulator catabolite control protein A (CcpA) is a global regulator of the Group A Streptococcus (GAS) transcriptome and contributes to GAS virulence in diverse infection sites. Herein, we studied the role of the maltose repressor (MalR), another LacI/GalR family member, in GAS global gene expression and virulence. MalR inactivation reduced GAS colonization of the mouse oropharynx but did not detrimentally affect invasive infection. The MalR transcriptome was limited to only 25 genes, and a highly conserved MalR DNA-binding sequence was identified. Variation of the MalR binding sequence significantly reduced MalR binding in vitro. In contrast, CcpA bound to the same DNA sequences as MalR but tolerated variation in the promoter sequences with minimal change in binding affinity. Inactivation of pulA, a MalR regulated gene which encodes a cell surface carbohydrate binding protein, significantly reduced GAS human epithelial cell adhesion and mouse oropharyngeal colonization but did not affect GAS invasive disease. These data delineate a molecular mechanism by which hierarchical regulation of carbon source utilization influences bacterial pathogenesis in a site-specific fashion.

Differential secretomics of Streptococcus pyogenes reveals a novel peroxide regulator (PerR)-regulated extracellular virulence factor mitogen factor 3 (MF3)

Streptococcus pyogenes is a human pathogen that causes various diseases. Numerous virulence factors secreted by S. pyogenes are involved in pathogenesis. The peroxide regulator (PerR) is associated with the peroxide resistance response and pathogenesis, but little is known about the regulation of the secretome involved in virulence. To investigate how PerR regulates the expression of the S. pyogenes secretome involved in virulence, a perR deficient mutant was used for comparative secretomic analysis with a wild-type strain. The conditioned medium containing secreted proteins of a wild-type strain and a perR deficient mutant at the stationary phase were collected for two-dimensional gel electrophoresis analysis, where protease inhibitors were applied to avoid the degradation of extracellular proteins. Differentially expressed protein spots were identified by liquid chromatography electrospray ionization tandem MS. More than 330 protein spots were detected on each gel. We identified 25 unique up-regulated proteins and 13 unique down-regulated proteins that were directly or indirectly controlled by the PerR regulator. Among these identified proteins, mitogen factor 3 (MF3), was selected to verify virulence and the expression of gene products. The data showed that MF3 protein levels in conditioned medium, as measured by immunoblot analysis, correlated well with protein levels determined by two-dimensional gel electrophoresis analysis. We also demonstrated that PerR bound to the promoter region of the mf3 gene. The result of an infection model showed that virulence was attenuated in the mf3 deficient mutant. Additional growth data of the wild-type strain and the mf3 deficient mutant suggested that MF3 played a role in digestion of exogenous DNA for promoting growth. To summarize, we conclude that PerR can positively regulate the expression of the secreted protein MF3 that contributes to the virulence in S. pyogenes. The analysis of the PerR-regulated secretome provided key information for the elucidation of the host-pathogen interactions and might assist in the development of potential chemotherapeutic strategies to prevent or treat streptococcal diseases.

Dispersal of Group A streptococcal biofilms by the cysteine protease SpeB leads to increased disease severity in a murine model

Group A Streptococcus (GAS) is a Gram-positive human pathogen best known for causing pharyngeal and mild skin infections. However, in the 1980's there was an increase in severe GAS infections including cellulitis and deeper tissue infections like necrotizing fasciitis. Particularly striking about this elevation in the incidence of severe disease was that those most often affected were previously healthy individuals. Several groups have shown that changes in gene content or regulation, as with proteases, may contribute to severe disease; yet strains harboring these proteases continue to cause mild disease as well. We and others have shown that group A streptococci (MGAS5005) reside within biofilms both in vitro and in vivo. That is to say that the organism colonizes a host surface and forms a 3-dimensional community encased in a protective matrix of extracellular protein, DNA and polysaccharide(s). However, the mechanism of assembly or dispersal of these structures is unclear, as is the relationship of these structures to disease outcome. Recently we reported that allelic replacement of the streptococcal regulator srv resulted in constitutive production of the streptococcal cysteine protease SpeB. We further showed that the constitutive production of SpeB significantly decreased MGAS5005Δsrv biofilm formation in vitro. Here we show that mice infected with MGAS5005Δsrv had significantly larger lesion development than wild-type infected animals. Histopathology, Gram-staining and immunofluorescence link the increased lesion development with lack of disease containment, lack of biofilm formation, and readily detectable levels of SpeB in the tissue. Treatment of MGAS5005Δsrv infected lesions with a chemical inhibitor of SpeB significantly reduced lesion formation and disease spread to wild-type levels. Furthermore, inactivation of speB in the MGAS5005Δsrv background reduced lesion formation to wild-type levels. Taken together, these data suggest a mechanism by which GAS disease may transition from mild to severe through the Srv mediated dispersal of GAS biofilms.

Naturally occurring single amino acid replacements in a regulatory protein alter streptococcal gene expression and virulence in mice

Infection with different strains of the same species of bacteria often results in vastly different clinical outcomes. Despite extensive investigation, the genetic basis of microbial strain-specific virulence remains poorly understood. Recent whole-genome sequencing has revealed that SNPs are the most prevalent form of genetic diversity among different strains of the same species of bacteria. For invasive serotype M3 group A streptococci (GAS) strains, the gene encoding regulator of proteinase B (RopB) has the highest frequency of SNPs. Here, we have determined that ropB polymorphisms alter RopB function and modulate GAS host-pathogen interactions. Sequencing of ropB in 171 invasive serotype M3 GAS strains identified 19 distinct ropB alleles. Inactivation of the ropB gene in strains producing distinct RopB variants had dramatically divergent effects on GAS global gene expression. Additionally, generation of isoallelic GAS strains differing only by a single amino acid in RopB confirmed that variant proteins affected transcript levels of the gene encoding streptococcal proteinase B, a major RopB-regulated virulence factor. Comparison of parental, RopB-inactivated, and RopB isoallelic strains in mouse infection models demonstrated that ropB polymorphisms influence GAS virulence and disease manifestations. These data detail a paradigm in which unbiased, whole-genome sequence analysis of populations of clinical bacterial isolates creates new avenues of productive investigation into the pathogenesis of common human infections.

Variation in M protein production among Streptococcus pyogenes strains according to emm genotype

M protein is an important virulence determinant in Streptococcus pyogenes, but the amounts of M protein in various strains of the species remain to be elucidated. To assess the amount of M protein in strains of each emm genotype, dot blot analysis was performed on 141 clinically isolated strains. Among the cell membrane-associated proteins, M protein was present in greater quantities in the emm1, 3, and 6 strains than in the other emm strains. In addition three strains, one each of the emm1, 3, and 6 types, showed prolific M protein production (M protein-high producers). These three emm genotypes are frequently isolated in clinical practice. Sequencing of the csrRS gene, one of the two-component signal transduction systems implicated in virulence, was performed on 25 strains bearing different amounts of M protein. CsrS mutations, in contrast to CsrR protein, were detected in 11 strains. The M protein-high producer strain of emm1 type carried two amino acid substitutions, whereas the other three emm1 strains carried only one substitution each. The M protein-high producer expressed its emm gene more strongly than the corresponding M protein-low producer did according to TaqMan RT-PCR. These observations suggest that the accumulation of amino acid substitutions in CsrS protein may contribute, at least in part, to the large amount of M protein production seen in several emm genotypes.

The Streptococcus pyogenes proteome: maps, virulence factors and vaccine candidates

Streptococcus pyogenes is an important cause of human morbidity and mortality worldwide. A wealth of genomic information related to this pathogen has facilitated exploration of the proteome, particularly in response to environmental conditions thought to mimic various aspects of pathogenesis. Proteomic approaches are also used to identify immunoreactive proteins for vaccine development and to identify proteins that may induce autoimmunity. These studies have revealed new mechanisms involved in regulating the S. pyogenes proteome, which has opened up new avenues in the study of S. pyogenes pathogenesis. This article describes the methods used, and progress being made towards characterizing the S. pyogenes proteome, including studies seeking to identify potential vaccine candidates.

Allelic replacement of the streptococcal cysteine protease SpeB in a Δsrv mutant background restores biofilm formation

Background

Group A Streptococcus (GAS) is a Gram-positive human pathogen that is capable of causing a wide spectrum of human disease. Thus, the organism has evolved to colonize a number of physiologically distinct host sites. One such mechanism to aid colonization is the formation of a biofilm. We have recently shown that inactivation of the streptococcal regulator of virulence (Srv), results in a mutant strain exhibiting a significant reduction in biofilm formation. Unlike the parental strain (MGAS5005), the streptococcal cysteine protease (SpeB) is constitutively produced by the srv mutant (MGAS5005Δsrv) suggesting Srv contributes to the control of SpeB production. Given that SpeB is a potent protease, we hypothesized that the biofilm deficient phenotype of the srv mutant was due to the constitutive production of SpeB. In support of this hypothesis, we have previously demonstrated that treating cultures with E64, a commercially available chemical inhibitor of cysteine proteases, restored the ability of MGAS5005Δsrv to form biofilms. Still, it was unclear if the loss of biofilm formation by MGAS5005Δsrv was due only to the constitutive production of SpeB or to other changes inherent in the srv mutant strain. To address this question, we constructed a ΔsrvΔspeB double mutant through allelic replacement (MGAS5005ΔsrvΔspeB) and tested its ability to form biofilms in vitro.

Findings

Allelic replacement of speB in the srv mutant background restored the ability of this strain to form biofilms under static and continuous flow conditions. Furthermore, addition of purified SpeB to actively growing wild-type cultures significantly inhibited biofilm formation.

Conclusions

The constitutive production of SpeB by the srv mutant strain is responsible for the significant reduction of biofilm formation previously observed. The double mutant supports a model by which Srv contributes to biofilm formation and/or dispersal through regulation of speB/SpeB.

Highly frequent mutations in negative regulators of multiple virulence genes in group A streptococcal toxic shock syndrome isolates

Streptococcal toxic shock syndrome (STSS) is a severe invasive infection characterized by the sudden onset of shock and multiorgan failure; it has a high mortality rate. Although a number of studies have attempted to determine the crucial factors behind the onset of STSS, the responsible genes in group A Streptococcus have not been clarified. We previously reported that mutations of csrS/csrR genes, a two-component negative regulator system for multiple virulence genes of Streptococcus pyogenes, are found among the isolates from STSS patients. In the present study, mutations of another negative regulator, rgg, were also found in clinical isolates of STSS patients. The rgg mutants from STSS clinical isolates enhanced lethality and impaired various organs in the mouse models, similar to the csrS mutants, and precluded their being killed by human neutrophils, mainly due to an overproduction of SLO. When we assessed the mutation frequency of csrS, csrR, and rgg genes among S. pyogenes isolates from STSS (164 isolates) and non-invasive infections (59 isolates), 57.3% of the STSS isolates had mutations of one or more genes among three genes, while isolates from patients with non-invasive disease had significantly fewer mutations in these genes (1.7%). The results of the present study suggest that mutations in the negative regulators csrS/csrR and rgg of S. pyogenes are crucial factors in the pathogenesis of STSS, as they lead to the overproduction of multiple virulence factors.

Group A streptococcus (GAS) causes life-threatening severe invasive diseases, including necrotizing fasciitis and streptococcal toxic shock-like syndrome. Although many studies have attempted to determine factors that are crucial for the onset of streptococcal toxic shock syndrome (STSS), bacterial factors responsible for it have not been clarified. By comparing genome sequences of clinical GAS isolates from STSS with those of non-invasive infections, we showed that mutations of negative regulator genes (csrS, csrR, rgg) were detected at a high frequency of more than 50% in STSS isolates, but at a low frequency of less than 2% in non-invasive isolates. These mutations of negative regulators were found in various emm-genotyped STSS isolates but not in a particular emm genotype. These mutants enhanced virulence in mouse models. Such results indicated that mutations of bacterial negative regulators are crucial for the pathogenesis of STSS due to the overproduction of multiple virulence factors under the de-repressed conditions.

Contribution of AmyA, an extracellular alpha-glucan degrading enzyme, to group A streptococcal host-pathogen interaction

alpha-Glucans such as starch and glycogen are abundant in the human oropharynx, the main site of group A Streptococcus (GAS) infection. However, the role in pathogenesis of GAS extracellular alpha-glucan binding and degrading enzymes is unknown. The serotype M1 GAS genome encodes two extracellular proteins putatively involved in alpha-glucan binding and degradation; pulA encodes a cell wall anchored pullulanase and amyA encodes a freely secreted putative cyclomaltodextrin alpha-glucanotransferase. Genetic inactivation of amyA, but not pulA, abolished GAS alpha-glucan degradation. The DeltaamyA strain had a slower rate of translocation across human pharyngeal epithelial cells. Consistent with this finding, the DeltaamyA strain was less virulent following mouse mucosal challenge. Recombinant AmyA degraded alpha-glucans into beta-cyclomaltodextrins that reduced pharyngeal cell transepithelial resistance, providing a physiologic explanation for the observed transepithelial migration phenotype. Higher amyA transcript levels were present in serotype M1 GAS strains causing invasive infection compared with strains causing pharyngitis. GAS proliferation in a defined alpha-glucan-containing medium was dependent on the presence of human salivary alpha-amylase. These data delineate the molecular mechanisms by which alpha-glucan degradation contributes to GAS host-pathogen interaction, including how GAS uses human salivary alpha-amylase for its own metabolic benefit.

Genome sequence of a nephritogenic and highly transformable M49 strain of Streptococcus pyogenes

The 1,815,783-bp genome of a serotype M49 strain of Streptococcus pyogenes (group A streptococcus [GAS]), strain NZ131, has been determined. This GAS strain (FCT type 3; emm pattern E), originally isolated from a case of acute post-streptococcal glomerulonephritis, is unusually competent for electrotransformation and has been used extensively as a model organism for both basic genetic and pathogenesis investigations. As with the previously sequenced S. pyogenes genomes, three unique prophages are a major source of genetic diversity. Two clustered regularly interspaced short palindromic repeat (CRISPR) regions were present in the genome, providing genetic information on previous prophage encounters. A unique cluster of genes was found in the pathogenicity island-like emm region that included a novel Nudix hydrolase, and, further, this cluster appears to be specific for serotype M49 and M82 strains. Nudix hydrolases eliminate potentially hazardous materials or prevent the unbalanced accumulation of normal metabolites; in bacteria, these enzymes may play a role in host cell invasion. Since M49 S. pyogenes strains have been known to be associated with skin infections, the Nudix hydrolase and its associated genes may have a role in facilitating survival in an environment that is more variable and unpredictable than the uniform warmth and moisture of the throat. The genome of NZ131 continues to shed light upon the evolutionary history of this human pathogen. Apparent horizontal transfer of genetic material has led to the existence of highly variable virulence-associated regions that are marked by multiple rearrangements and genetic diversification while other regions, even those associated with virulence, vary little between genomes. The genome regions that encode surface gene products that will interact with host targets or aid in immune avoidance are the ones that display the most sequence diversity. Thus, while natural selection favors stability in much of the genome, it favors diversity in these regions.

Molecular mechanisms underlying group A streptococcal pathogenesis

Group A Streptococcus (GAS) is a versatile human pathogen causing diseases ranging from uncomplicated mucosal infections to life-threatening invasive disease. The development of human-relevant animal models of GAS infection and introduction of new technologies have markedly accelerated the pace of discoveries related to GAS host-pathogen interactions. For example, recently investigators have identified pili on the GAS cell surface and learned that they are key components for adherence to eukaryotic cell surfaces. Similarly, the recent development of a transgenic mouse expressing human plasminogen has resulted in new understanding of the molecular processes contributing to invasive infection. Improved understanding of the molecular mechanisms underlying the pathogenesis of GAS pharyngeal, invasive and other infections holds the promise of assisting with the development of novel preventive or therapeutic agents for this prevalent human pathogen.

Molecular characterization of group A Streptococcus maltodextrin catabolism and its role in pharyngitis

We previously demonstrated that the cell-surface lipoprotein MalE contributes to GAS maltose/maltodextrin utilization, but MalE inactivation does not completely abrogate GAS catabolism of maltose or maltotriose. Using a genome-wide approach, we identified the GAS phosphotransferase system (PTS) responsible for non-MalE maltose/maltotriose transport. This PTS is encoded by an open reading frame (M5005_spy1692) previously annotated as ptsG based on homology with the glucose PTS in Bacillus subtilis. Genetic inactivation of M5005_spy1692 significantly reduced transport rates of radiolabelled maltose and maltotriose, but not glucose, leading us to propose its reannotation as malT for maltose transporter. The DeltamalT, DeltamalE and DeltamalE:malT strains were significantly attenuated in their growth in human saliva and in their ability to catabolize alpha-glucans digested by purified human salivary alpha-amylase. Compared with wild-type, the three isogenic mutant strains were significantly impaired in their ability to colonize the mouse oropharynx. Finally, we discovered that the transcript levels of maltodextrin utilization genes are regulated by competitive binding of the maltose repressor MalR and catabolite control protein A. These data provide novel insights into regulation of the GAS maltodextrin genes and their role in GAS host-pathogen interaction, thereby increasing the understanding of links between nutrient acquisition and virulence in common human pathogens.

Novel algorithms reveal streptococcal transcriptomes and clues about undefined genes

Bacteria-host interactions are dynamic processes, and understanding transcriptional responses that directly or indirectly regulate the expression of genes involved in initial infection stages would illuminate the molecular events that result in host colonization. We used oligonucleotide microarrays to monitor (in vitro) differential gene expression in group A streptococci during pharyngeal cell adherence, the first overt infection stage. We present neighbor clustering, a new computational method for further analyzing bacterial microarray data that combines two informative characteristics of bacterial genes that share common function or regulation: (1) similar gene expression profiles (i.e., co-expression); and (2) physical proximity of genes on the chromosome. This method identifies statistically significant clusters of co-expressed gene neighbors that potentially share common function or regulation by coupling statistically analyzed gene expression profiles with the chromosomal position of genes. We applied this method to our own data and to those of others, and we show that it identified a greater number of differentially expressed genes, facilitating the reconstruction of more multimeric proteins and complete metabolic pathways than would have been possible without its application. We assessed the biological significance of two identified genes by assaying deletion mutants for adherence in vitro and show that neighbor clustering indeed provides biologically relevant data. Neighbor clustering provides a more comprehensive view of the molecular responses of streptococci during pharyngeal cell adherence.

Inter- and intraserotypic variation in the Streptococcus pyogenes Rgg regulon

Human isolates of Streptococcus pyogenes, a Gram-positive bacterium, are characterized by significant genetic and phenotypic variation. The rgg locus, also known as ropB, is a global transcriptional regulator of genes associated with metabolism, stress responses, and virulence in S. pyogenes strain NZ131 (serotype M49). To assess the breadth of the Rgg regulon, the rgg gene was inactivated in three additional strains representing serotypes M1 (strains SF370 and MGAS5005) and M49 (strain CS101). Changes in gene expression were identified in the postexponential phase of growth using Affymetrix NimbleExpress Arrays. The results identified an Rgg core-regulon consisting of speB and adjacent hypothetical protein gene, spy2040, and a variable and strain-specific subregulon, ranging in size from a single gene (spy1793) in strain MGAS5005 to 43 genes in strain SF370. Thus, both interserotypic and intraserotypic variation is characteristic of the Rgg regulon in S. pyogenes.

Deficiency of the Rgg regulator promotes H2O2 resistance, AhpCF-mediated H2O2 decomposition, and virulence in Streptococcus pyogenes

Streptococcus pyogenes (group A streptococcus [GAS]), a catalase-negative gram-positive bacterium, is aerotolerant and survives H2O2 exposures that kill many catalase-positive bacteria. The molecular basis of the H2O2 resistance is poorly known. Here, we demonstrate that serotype M49 GAS lacking the Rgg regulator is more resistant to H2O2 and also decomposes more H2O2 than the parental strain. Subgenomic transcriptional profiling and genome-integrated green fluorescent protein reporters showed that a bicistronic operon, a homolog of the Streptococcus mutans ahpCF operon, is transcriptionally up-regulated in the absence of Rgg. Phenotypic assays with ahpCF operon knockouts demonstrated that the gene products decompose H2O2 and protect GAS against peroxide stress. In a murine intraperitoneal-infection model, Rgg deficiency increased the virulence of GAS, although in an ahpCF-independent manner. Rgg-mediated repression of H2O2 resistance is divergent from the previously characterized peroxide resistance repressor PerR. Moreover, Rgg-mediated repression of H2O2 resistance is inducible by cellular stresses of diverse natures--ethanol, organic hydroperoxide, and H2O2. Rgg is thus identified as a novel sensoregulator of streptococcal H2O2 resistance with potential implications for the virulence of the catalase-negative GAS.

Regulation of polysaccharide utilization contributes to the persistence of group a streptococcus in the oropharynx

Group A Streptococcus (GAS) genes that encode proteins putatively involved in polysaccharide utilization show growth phase-dependent expression in human saliva. We sought to determine whether the putative polysaccharide transcriptional regulator MalR influences the expression of such genes and whether MalR helps GAS infect the oropharynx. Analysis of 32 strains of 17 distinct M protein serotypes revealed that MalR is highly conserved across GAS strains. malR transcripts were detectable in patients with GAS pharyngitis, and the levels increased significantly during growth in human saliva compared to the levels during growth in glucose-containing or nutrient-rich media. To determine if MalR influenced the expression of polysaccharide utilization genes, we compared the transcript levels of eight genes encoding putative polysaccharide utilization proteins in the parental serotype M1 strain MGAS5005 and its DeltamalR isogenic mutant derivative. The transcript levels of all eight genes were significantly increased in the DeltamalR strain compared to the parental strain, especially during growth in human saliva. Following experimental infection, the DeltamalR strain persistently colonized the oropharynx in significantly fewer mice than the parental strain colonized, and the numbers of DeltamalR strain CFU recovered were significantly lower than the numbers of the parental strain CFU recovered. These data led us to conclude that MalR influences the expression of genes putatively involved in polysaccharide utilization and that MalR contributes to the persistence of GAS in the oropharynx.

Global analysis of community-associated methicillin-resistant Staphylococcus aureus exoproteins reveals molecules produced in vitro and during infection

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is a threat to human health worldwide. Although progress has been made, mechanisms of CA-MRSA pathogenesis are poorly understood and a comprehensive analysis of CA-MRSA exoproteins has not been conducted. To address that deficiency, we used proteomics to identify exoproteins made by MW2 (USA400) and LAC (USA300) during growth in vitro. Two hundred and fifty unique exoproteins were identified by 2-dimensional gel electrophoresis coupled with automated direct infusion-tandem mass spectrometry (ADI-MS/MS) analysis. Eleven known virulence-related exoproteins differed in abundance between the strains, including alpha-haemolysin (Hla), collagen adhesin (Cna), staphylokinase (Sak), coagulase (Coa), lipase (Lip), enterotoxin C3 (Sec3), enterotoxin Q (Seq), V8 protease (SspA) and cysteine protease (SspB). Mice infected with MW2 or LAC produced antibodies specific for known or putative virulence factors, such as autolysin (Atl), Cna, Ear, ferritin (Ftn), Lip, 1-phosphatidylinositol phosphodiesterase (Plc), Sak, Sec3 and SspB, indicating the exoproteins are made during infection in vivo. We used confocal microscopy to demonstrate aureolysin (Aur), Hla, SspA and SspB are produced following phagocytosis by human neutrophils, thereby linking exoprotein production in vitro with that during host-pathogen interaction. We conclude that the exoproteins identified herein likely account in part for the success of CA-MRSA as a human pathogen.

Crucial role of antioxidant proteins and hydrolytic enzymes in pathogenicity of Penicillium expansum: analysis based on proteomics approach

Penicillium expansum, a widespread filamentous fungus, is a major causative agent of fruit decay and may lead to the production of mycotoxin that causes harmful effects on human health. In this study, we compared the cellular and extracellular proteomes of P. expansum in the absence and presence of borate, which affects the virulence of the fungal pathogen. The differentially expressed proteins were identified using ESI-Q-TOF-MS/MS. Several proteins related to stress response (glutathione S-transferase, catalase, and heat shock protein 60) and basic metabolism (glyceraldehyde-3-phosphate dehydrogenase, dihydroxy-acid dehydratase, and arginase) were identified in the cellular proteome. Catalase and glutathione S-transferase, the two antioxidant enzymes, exhibited reduced levels of expression upon exposure to borate. Because catalase and glutathione S-transferase are related to oxidative stress response, we further investigated the reactive oxygen species (ROS) levels and oxidative protein carbonylation (damaged proteins) in P. expansum. Higher amounts of ROS and carbonylated proteins were observed after borate treatment, indicating that catalase and glutathione S-transferase are important in scavenging ROS and protecting cellular proteins from oxidative damage. Additionally to find secretory proteins that contribute to the virulence, we studied the extracellular proteome of P. expansum under stress condition with reduced virulence. The expression of three protein spots were repressed in the presence of borate and identified as the same hydrolytic enzyme, polygalacturonase.

The transcriptional regulator RovS controls the attachment of Streptococcus agalactiae to human epithelial cells and the expression of virulence genes

Streptococcus agalactiae is part of the normal flora of the human gastrointestinal tract and also the leading cause of bacterial infections in human newborns and immunocompromised adults. The colonization and infection of different regions within the human host require a regulatory network in S. agalactiae that senses environmental stimuli and controls the formation of specific virulence factors. In the present study, we characterized an Rgg-like transcriptional regulator, designated RovS (regulator of virulence in Streptococcus agalactiae). Deletion of the rovS gene in the genome of S. agalactiae resulted in strain 6313 DeltarovS, which exhibited an increased attachment to immobilized fibrinogen and a significant increase in adherence to the eukaryotic lung epithelial cell line A549. Quantification of expression levels of known and putative S. agalactiae virulence genes by real-time PCR revealed that RovS influences the expression of fbsA, gbs0230, sodA, rogB, and the cyl operon. The altered gene expression in mutant 6313 DeltarovS was restored by plasmid-mediated expression of rovS, confirming the RovS deficiency as the cause for the observed changes in virulence gene expression in S. agalactiae. DNA electrophoretic mobility shift assays showed that RovS specifically binds to the promoter regions of fbsA, gbs0230, sodA, and the cyl operon, indicating that RovS directly regulates their expression. Deletion and mutation studies in the promoter region of fbsA, encoding the main fibrinogen receptor in S. agalactiae, identified a RovS DNA motif. Similar motifs were also found in the promoter regions of gbs0230, sodA, and the cyl operon, and alignments allowed us to propose a consensus sequence for the DNA-binding site of RovS.

Contribution of invariant residues to the function of Rgg family transcription regulators

The Rgg family of transcription regulators is widely distributed among gram-positive bacteria, yet how these proteins control transcription is poorly understood. Using Streptococcus pyogenes RopB as a model, we demonstrated that residues invariant among Rgg-like regulators are critical for function and obtained evidence for a mechanism involving protein complex formation.

Inactivation of the group A Streptococcus regulator srv results in chromosome wide reduction of transcript levels, and changes in extracellular levels of Sic and SpeB

Group A Streptococcus is characterized by the ability to cause a diverse number of human infections including pharyngitis, necrotizing fasciitis, toxic shock syndrome, and acute rheumatic fever, yet the regulation of streptococcal genes involved in disease processes and survival in the host is not completely understood. Genome scale analysis has revealed a complex regulatory network including 13 two-component regulatory systems and more than 100 additional putative regulators, the majority of which remain uncharacterized. Among these is the streptococcal regulator of virulence, Srv, the first Group A Streptococcus member of the Crp/Fnr family of transcriptional regulators. Previous work demonstrated that the loss of srv resulted in a significant decrease in Group A Streptococcus virulence. To begin to define the gene products influenced by Srv, we combined microarray and two-dimensional gel electrophoresis analysis. Loss of srv results in a chromosome wide reduction of gene transcription and changes in the production of the extracellular virulence factors Sic (streptococcal inhibitor of complement) and SpeB (cysteine proteinase). Sic levels are reduced in the srv mutant, whereas the extracellular concentration and activity of SpeB is increased. These data link Srv to the increasingly complex GAS regulatory network.

Defining the Mga regulon: comparative transcriptome analysis reveals both direct and indirect regulation by Mga in the group A streptococcus

The regulator Mga in the group A streptococcus (GAS) is known to directly activate several virulence genes important for colonization and immune evasion. Transcriptome analysis comparing two mga-1 serotypes (M1 SF370, M6 JRS4) and one mga-2 serotype (M4 GA40634) against their isogenic mga-inactivated strains uncovered a broader Mga regulon profile containing both activated and repressed genes with predicted functions primarily related to sugar metabolism. This was reflected in the altered abilities of M1 and M4 Mga mutants to grow in chemically defined media with a single sugar source compared with their wild-type counterparts. Although the M1 and M4 Mga profiles were similar, the M6 JRS4 was clearly distinct, even from other M6 strains. Real-time RT-PCR and Northern blots confirmed that established core Mga regulon genes directly activated by Mga (emm, scpA, sof, fba) exhibited the highest activation levels across all strains tested. Spy2036 encoding a cytosolic hypothetical protein was highly activated in all three serotypes and was called gene regulated by Mga (grm). Mga bound directly to Pgrm, which overlaps the Mga-regulated Psof in OF+ strains, suggesting that grm is part of the core Mga regulon and Mga is able to activate divergently transcribed genes from a single site. Furthermore, Mga activated speB when detectable in the wild-type strain, although direct binding of Mga to PspeB could not be demonstrated. Thus, Mga is able to both directly and indirectly regulate genes shown to be important for virulence and the metabolic homeostasis of GAS.

Maltodextrin utilization plays a key role in the ability of group A Streptococcus to colonize the oropharynx

Analysis of multiple group A Streptococcus (GAS) genomes shows that genes encoding proteins involved in carbohydrate utilization comprise some 15% of the core GAS genome. Yet there is a limited understanding of how carbohydrate utilization contributes to GAS pathogenesis. Previous genome-wide GAS studies led us to a focused investigation of MalE, a putative maltodextrin-binding protein. Analysis of 28 strains of 22 distinct M protein serotypes showed that MalE is highly conserved among diverse GAS strains. malE transcript levels were significantly increased during growth in human saliva compared to growth in a chemically defined glucose-containing medium or a nutrient-rich medium. MalE was accessible to antibody binding, indicating that it is expressed on the GAS cell surface. Moreover, growth in human saliva appeared to increase MalE surface expression compared to growth in a nutrient-rich medium. Analysis of a delta malE isogenic mutant strain revealed decreased growth in human saliva compared to wild-type GAS. Radiolabeled carbohydrate binding assays showed that MalE was required for the binding of maltose but not glucose. The delta malE isogenic mutant strain colonized a lower percentage of GAS-challenged mice compared to wild-type and genetically complemented strains. Furthermore, decreased numbers of CFU were recovered from mice infected with the delta malE strain compared to those infected with wild-type GAS. These data demonstrate that maltodextrin acquisition is likely to be a key factor in the ability of GAS to successfully infect the oropharynx. Further investigation into carbohydrate transport and metabolism pathways may yield novel insights into GAS pathogenesis.

Adaptive response of Yersinia pestis to extracellular effectors of innate immunity during bubonic plague

Yersinia pestis causes bubonic plague, characterized by an enlarged, painful lymph node, termed a bubo, that develops after bacterial dissemination from a fleabite site. In susceptible animals, the bacteria rapidly escape containment in the lymph node, spread systemically through the blood, and produce fatal sepsis. The fulminant progression of disease has been largely ascribed to the ability of Y. pestis to avoid phagocytosis and exposure to antimicrobial effectors of innate immunity. In vivo microarray analysis of Y. pestis gene expression, however, revealed an adaptive response to nitric oxide (NO)-derived reactive nitrogen species and to iron limitation in the extracellular environment of the bubo. Polymorphonuclear neutrophils recruited to the infected lymph node expressed abundant inducible NO synthase, and several Y. pestis homologs of genes involved in the protective response to reactive nitrogen species were up-regulated in the bubo. Mutation of one of these genes, which encodes the Hmp flavohemoglobin that detoxifies NO, attenuated virulence. Thus, the ability of Y. pestis to destroy immune cells and remain extracellular in the bubo appears to limit exposure to some but not all innate immune effectors. High NO levels induced during plague may also influence the developing adaptive immune response and contribute to septic shock.

The rggC locus, with a frameshift mutation, is involved in oxidative stress response by Streptococcus thermophilus

In Streptococcus thermophilus, the locus rggC contains a frameshift mutation and thus consists of two open reading frames (ORFs), rggC (1) and rggC (2), which encode proteins exhibiting similarity with the Rgg transcriptional regulator family. In this work, mutants showing a partial deletion of rggC (1) and rggC (2 )were constructed and their response to menadione, a superoxide-generating compound, was analysed. These mutants exhibited different behaviour to this oxidative stress compared with the wild-type strain. Analysis of this locus among 21 strains of S. thermophilus showed a polythymine tract length variability and a strain-dependant adenine residue could be found upstream of this repeat. This interstrain polymorphism supports evidence for the hypothesis that the rggC locus is phase variable.

Characterization of late acyltransferase genes of Yersinia pestis and their role in temperature-dependent lipid A variation

Yersinia pestis is an important human pathogen that is maintained in flea-rodent enzootic cycles in many parts of the world. During its life cycle, Y. pestis senses host-specific environmental cues such as temperature and regulates gene expression appropriately to adapt to the insect or mammalian host. For example, Y. pestis synthesizes different forms of lipid A when grown at temperatures corresponding to the in vivo environments of the mammalian host and the flea vector. At 37 degrees C, tetra-acylated lipid A is the major form; but at 26 degrees C or below, hexa-acylated lipid A predominates. In this study, we show that the Y. pestis msbB (lpxM) and lpxP homologs encode the acyltransferases that add C12 and C(16:1) groups, respectively, to lipid IV(A) to generate the hexa-acylated form, and that their expression is upregulated at 21 degrees C in vitro and in the flea midgut. A Y. pestis deltamsbB deltalpxP double mutant that did not produce hexa-acylated lipid A was more sensitive to cecropin A, but not to polymyxin B. This mutant was able to infect and block fleas as well as the parental wild-type strain, indicating that the low-temperature-dependent change to hexa-acylated lipid A synthesis is not required for survival in the flea gut.

Regulation of SpeB in Streptococcus pyogenes by pH and NaCl: a model for in vivo gene expression

For a pathogen such as Streptococcus pyogenes, ecological success is determined by its ability to sense the environment and mount an appropriate adaptive transcriptional response. Thus, determining conditions for analyses of gene expression in vitro that are representative of the in vivo environment is critical for understanding the contributions of transcriptional response pathways to pathogenesis. In this study, we determined that the gene encoding the SpeB cysteine protease is up-regulated over the course of infection in a murine soft-tissue model. Conditions were identified, including growth phase, acidic pH, and an NaCl concentration of <0.1 M, that were required for expression of speB in vitro. Analysis of global expression profiles in response to these conditions in vitro identified a set of coregulated genes whose expression patterns showed a significant correlation with that of speB when examined during infection of murine soft tissues. This analysis revealed that a culture medium that promotes high levels of SpeB expression in vitro produced an expression profile that showed significant correlation to the profile observed in vivo. Taken together, these studies establish culture conditions that mimic in vivo expression patterns; that growth phase, pH, and NaCl may mimic relevant cues sensed by S. pyogenes during infection; and that identification of other environmental cues that alter expression of speB in vitro may provide insight into the signals that direct global patterns of gene expression in vivo.

Enhancement of streptolysin O activity and intrinsic cytotoxic effects of the group A streptococcal toxin, NAD-glycohydrolase

Streptolysin O (SLO) is a cholesterol-dependent cytolysin produced by the important human pathogen, group A Streptococcus (Streptococcus pyogenes or GAS). In addition to its cytolytic activity, SLO mediates the translocation of GAS NAD-glycohydrolase (NADase) into human epithelial cells in vitro. Production of both NADase and SLO is associated with augmented host cell injury beyond that produced by SLO alone, but the mechanism of enhanced cytotoxicity is not known. We have now shown that expression of NADase together with SLO dramatically enhanced the lytic activity of GAS culture supernatants for erythrocytes but had no effect on SLO-mediated poration of synthetic cholesterol-rich liposomes. This result revealed a previously unknown contribution of NADase to the cytolytic activity associated with GAS production of SLO. Purified recombinant SLO bound NADase in vitro, supporting a specific, physical interaction of the two proteins. Exposure of human keratinocytes to wild-type GAS, but not to a NADase-deficient mutant strain, resulted in profound depletion of cellular NAD+ and ATP. Furthermore, expression of recombinant GAS NADase in yeast, in the absence of SLO, induced growth arrest, depletion of NAD+ and ATP, and cell death. These findings have provided evidence that the augmentation of SLO-mediated cytotoxicity by NADase is a consequence of depletion of host cell energy stores through the enzymatic action of NADase. Together, the results have provided mechanistic insight into the cytotoxic effects of a unique bipartite bacterial toxin.

Central role of a bacterial two-component gene regulatory system of previously unknown function in pathogen persistence in human saliva

The molecular genetic mechanisms used by bacteria to persist in humans are poorly understood. Group A Streptococcus (GAS) causes the majority of bacterial pharyngitis cases in humans and is prone to persistently inhabit the upper respiratory tract. To gain information about how GAS survives in and infects the oropharynx, we analyzed the transcriptome of a serotype M1 strain grown in saliva. The dynamic pattern of changes in transcripts of genes [spy0874/0875, herein named sptR and sptS (sptR/S), for saliva persistence] encoding a two-component gene regulatory system of unknown function suggested that SptR/S contributed to persistence of GAS in saliva. Consistent with this idea, an isogenic nonpolar mutant strain (DeltasptR) was dramatically less able to survive in saliva compared with the parental strain. Iterative expression microarray analysis of bacteria grown in saliva revealed that transcripts of several known and putative GAS virulence factor genes were decreased significantly in the DeltasptR mutant strain. Compared with the parental strain, the isogenic mutant strain also had altered transcripts of multiple genes encoding proteins involved in complex carbohydrate acquisition and utilization pathways. Western immunoblot analysis and real-time PCR analysis of GAS in throat swabs taken from humans with pharyngitis confirmed the findings. We conclude that SptR/S optimizes persistence of GAS in human saliva, apparently by strategically influencing metabolic pathways and virulence factor production. The discovery of a genetic program that significantly increased persistence of a major human pathogen in saliva enhances understanding of how bacteria survive in the host and suggests new therapeutic strategies.

The Protein Expression of Streptococcus pyogenes Is Significantly Influenced by Human Plasma

During the course of infection, the common human pathogen Streptococcus pyogenes encounters plasma. We show that plasma causes S. pyogenes to rapidly remodel its cellular metabolism and virulence pathways. We also identified a variant of the major virulence factor, M1 protein, lacking 13 amino acids at the NH(2)-terminus in bacteria grown with plasma. The pronounced effect of plasma on protein expression, suggests this is an important adaptive mechanism with implications for S. pyogenes pathogenicity.

SpeB-Spi: a novel protease-inhibitor pair from Streptococcus pyogenes

This study presents evidence for a novel protease-protease inhibitor couple, SpeB-Spi, in the human pathogen Streptococcus pyogenes. The gene for the inhibitor Spi is located directly downstream of the gene for the streptococcal cysteine protease SpeB. Spi is 37% identical and 70% similar to the sequence of the SpeB propeptide, suggesting that Spi and the SpeB propeptide might bind to SpeB in an analogous manner. Secondary structure predictions and molecular modelling suggested that Spi would adopt a structure similar to the SpeB propeptide. The spi gene was co-transcribed with speB on the 1.7 knt and 2.2 knt transcripts previously identified for speB. The Spi protein was purified by SpeB-affinity chromatography from the S. pyogenes cytoplasm. Recombinant Spi was produced and purified, and shown to bind to SpeB and to inhibit its protease activity. Although a similar genetic arrangement of protease and inhibitor is present in staphylococci, this is the first example of an inhibitor molecule that is a structural homologue of the cognate propeptide, and which is genetically linked to the protease gene. Thus, this represents a novel system whereby bacteria may control the intracellular activity of their proteases.

Surface analyses and immune reactivities of major cell wall-associated proteins of group a streptococcus

A proteomic analysis was undertaken to identify cell wall-associated proteins of Streptococcus pyogenes. Seventy-four distinct cell wall-associated proteins were identified, 66 of which were novel. Thirty-three proteins were immunoreactive with pooled S. pyogenes-reactive human antisera. Biotinylation of the GAS cell surface identified 23 cell wall-associated proteins that are surface exposed.