The catabolite control protein CcpA binds to Pmga and influences expression of the virulence regulator Mga in the Group A streptococcus

Novel motif associated with carbon catabolite repression in two major Gram-positive pathogen virulence regulatory proteins

Carbon catabolite repression (CCR) is a widely conserved regulatory process that ensures enzymes and transporters of less-preferred carbohydrates are transcriptionally repressed in the presence of a preferred carbohydrate. This phenomenon can be regulated via a CcpA-dependent or CcpA-independent mechanism. The CcpA-independent mechanism typically requires a transcriptional regulator harboring a phosphotransferase regulatory domain (PRD) that interacts with phosphotransferase system (PTS) components. PRDs contain a conserved histidine residue that is phosphorylated by the PTS-associated HPr-His15~P protein. PRD-containing regulators often harbor additional domains that resemble PTS-associated EIIB protein domains with a conserved cysteine residue that can be phosphorylated by cognate PTS components. We noted that Mga, the PRD-containing central virulence regulator of Streptococcus pyogenes, has an EIIBGat domain containing a cysteine that, based on the presence of a similar motif in glycerol kinase, could be a target for phosphorylation. Using site-directed mutagenesis, we constructed phospho-ablative and phospho-mimetic substitutions of this cysteine and found that these substitutions modify the CCR of the Rgg2/3 quorum-sensing system. Moreover, we provide genetic evidence that the phospho-donor of this cysteine residue is likely to be ManL, the EIIA/B subunit of the mannose PTS system. Interestingly, a structurally distinct virulence gene regulator, PrfA of Listeria monocytogenes, harbors a similar cysteine-containing motif, and phospho-ablative and phospho-mimetic substitutions of the cysteine-altered CCR of PrfA-dependent virulence gene expression. Collectively, our data suggest that phosphorylation of a cysteine within the shared novel motif in Mga and PrfA may be a heretofore missing link between cellular metabolism and virulence.IMPORTANCEIn this study, we identified a novel cysteine-containing motif within the amino acid sequence of two structurally distinct transcriptional regulators of virulence in two Gram-positive pathogens that appears to link carbon metabolism with virulence gene expression. The results also highlight the potential post-translational modification of cysteine in bacterial species, a rare and understudied modification.

Molecular Targets in Streptococcus pyogenes for the Development of Anti-Virulence Agents

Streptococcus pyogenes, commonly known as Group A Streptococcus (GAS), is a significant human pathogen responsible for a wide range of diseases, from mild pharyngitis to severe conditions such as necrotizing fasciitis and toxic shock syndrome. The increasing antibiotic resistance, especially against macrolide antibiotics, poses a challenge to the effective treatment of these infections. This paper reviews the current state and mechanisms of antibiotic resistance in S. pyogenes. Furthermore, molecular targets for developing anti-virulence agents, which aim to attenuate virulence rather than killing it outright, are explored. This review specifically focuses on virulence regulators, proteins that coordinate the expression of multiple virulence factors in response to environmental signals, playing a crucial role in the pathogen's ability to cause disease. Key regulatory systems, such as RopB, Mga, CovRS, and the c-di-AMP signaling system, are discussed for their roles in modulating virulence gene expression. Additionally, potential molecular target sites for the development of anti-virulence agents are suggested. By concentrating on these regulatory pathways, it is proposed that anti-virulence strategies could enhance the effectiveness of existing antibiotics and reduce the selective pressure that drives the development of resistance.

Group A Streptococcus adaptation to diverse niches: lessons from transcriptomic studies

Group A Streptococcus (GAS) is a major human pathogen, causing diseases ranging from mild superficial infections of the skin and pharyngeal epithelium to severe systemic and invasive diseases. Moreover, post infection auto-immune sequelae arise by a yet not fully understood mechanism. The ability of GAS to cause a wide variety of infections is linked to the expression of a large set of virulence factors and their transcriptional regulation in response to various physiological environments. The use of transcriptomics, among others -omics technologies, in addition to traditional molecular methods, has led to a better understanding of GAS pathogenesis and host adaptation mechanisms. This review focusing on bacterial transcriptomic provides new insight into gene-expression patterns in vitro, ex vivo and in vivo with an emphasis on metabolic shifts, virulence genes expression and transcriptional regulators role.

Ultrasound-assisted extraction of emodin from Rheum officinale Baill and its antibacterial mechanism against Streptococcus suis based on CcpA

Emodin was extracted from Rheum officinale Baill by ultrasound-assisted extraction (UAE), and ethanol was chosen as the suitable solvent through SEM and molecular dynamic simulation. Under the optimum conditions (power 541 W, time 23 min, liquid to material ratio 13:1 mL/g, ethanol concentration 83 %) predicted by RSM, the yield of emodin was 2.18 ± 0.11 mg/g. Moreover, ultrasound power and time displayed the significant effects on the extraction process. Extracting dynamics analysis indicated that the extraction process of emodin by UAE conformed to Fick's second diffusion law. The results of antibacterial experiments suggested that emodin can damage cell membrane and inhibit the expression of cps2A, sao, mrp, epf, neu and the hemolytic activity of S. suis. Biolayer interferometry and FT-IR multi-peak fitting assays demonstrated that emodin induced a secondary conformational shift in CcpA. Molecular docking and molecular dynamics confirmed that emodin bound to CcpA through hydrogen bonding (ALA248, GLU249, GLY129 and ASN196) and π-π T-shaped interaction (TYR225 and TYR130), and the mutation of amino acid residues affected the affinity of CcpA to emodin. Therefore, emodin inhibited the sugar utilization of S. suis through binding to CcpA, and CcpA may be a potential target to inhibit the growth of S. suis.

Group B Streptococcus Cas9 variants provide insight into programmable gene repression and CRISPR-Cas transcriptional effects

Group B Streptococcus (GBS; S. agalactiae) causes chorioamnionitis, neonatal sepsis, and can also cause disease in healthy or immunocompromised adults. GBS possesses a type II-A CRISPR-Cas9 system, which defends against foreign DNA within the bacterial cell. Several recent publications have shown that GBS Cas9 influences genome-wide transcription through a mechanism uncoupled from its function as a specific, RNA-programmable endonuclease. We examine GBS Cas9 effects on genome-wide transcription through generation of several isogenic variants with specific functional defects. We compare whole-genome RNA-seq from Δcas9 GBS with a full-length Cas9 gene deletion; dcas9 defective in its ability to cleave DNA but still able to bind to frequently occurring protospacer adjacent motifs; and scas9 that retains its catalytic domains but is unable to bind protospacer adjacent motifs. Comparing scas9 GBS to the other variants, we identify nonspecific protospacer adjacent motif binding as a driver of genome-wide, Cas9 transcriptional effects in GBS. We also show that Cas9 transcriptional effects from nonspecific scanning tend to influence genes involved in bacterial defense and nucleotide or carbohydrate transport and metabolism. While genome-wide transcription effects are detectable by analysis of next-generation sequencing, they do not result in virulence changes in a mouse model of sepsis. We also demonstrate that catalytically inactive dCas9 expressed from the GBS chromosome can be used with a straightforward, plasmid-based, single guide RNA expression system to suppress transcription of specific GBS genes without potentially confounding off-target effects. We anticipate that this system will be useful for study of nonessential and essential gene roles in GBS physiology and pathogenesis.

Group B Streptococcus Cas9 variants provide insight into programmable gene repression and CRISPR-Cas transcriptional effects

Group B Streptococcus (GBS; S. agalactiae ) causes chorioamnionitis, neonatal sepsis, and can also cause disease in healthy or immunocompromised adults. GBS possesses a type II-A CRISPR-Cas9 system, which defends against foreign DNA within the bacterial cell. Several recent publications have shown that GBS Cas9 influences genome-wide transcription through a mechanism uncoupled from its function as a specific, RNA-programmable endonuclease. We examine GBS Cas9 effects on genome-wide transcription through generation of several isogenic variants with specific functional defects. We compare whole-genome RNA-seq from Δ cas9 GBS with a full-length Cas9 gene deletion; dcas9 defective in its ability to cleave DNA but still able to bind to frequently occurring protospacer adjacent motifs; and scas9 that retains its catalytic domains but is unable to bind protospacer adjacent motifs. Comparing scas9 GBS to the other variants, we identify nonspecific protospacer adjacent motif binding as a driver of genome-wide, Cas9 transcriptional effects in GBS. We also show that Cas9 transcriptional effects from nonspecific scanning tend to influence genes involved in bacterial defense and nucleotide or carbohydrate transport and metabolism. While genome-wide transcription effects are detectable by analysis of next-generation sequencing, they do not result in virulence changes in a mouse model of sepsis. We also demonstrate that catalytically inactive dCas9 expressed from the GBS chromosome can be used with a straightforward, plasmid-based, single guide RNA expression system to suppress transcription of specific GBS genes without potentially confounding off-target effects. We anticipate that this system will be useful for study of nonessential and essential gene roles in GBS physiology and pathogenesis.

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.

Role of Metabolic Adaptation of Streptococcus suis to Host Niches in Bacterial Fitness and Virulence

Streptococcus suis, both a common colonizer of the porcine upper respiratory tract and an invasive pig pathogen, successfully adapts to different host environments encountered during infection. Whereas the initial infection mainly occurs via the respiratory tract, in a second step, the pathogen can breach the epithelial barrier and disseminate within the whole body. Thereby, the pathogen reaches other organs such as the heart, the joints, or the brain. In this review, we focus on the role of S. suis metabolism for adaptation to these different in vivo host niches to encounter changes in nutrient availability, host defense mechanisms and competing microbiota. Furthermore, we highlight the close link between S. suis metabolism and virulence. Mutants deficient in metabolic regulators often show an attenuation in infection experiments possibly due to downregulation of virulence factors, reduced resistance to nutritive or oxidative stress and to phagocytic activity. Finally, metabolic pathways as potential targets for new therapeutic strategies are discussed. As antimicrobial resistance in S. suis isolates has increased over the last years, the development of new antibiotics is of utmost importance to successfully fight infections in the future.

Glucose Phosphotransferase System Modulates Pyruvate Metabolism, Bacterial Fitness, and Microbial Ecology in Oral Streptococci

Spontaneous mutants with defects in the primary glucose phosphotransferase permease (manLMNO) of Streptococcus sanguinis SK36 showed enhanced fitness at low pH. Transcriptomics and metabolomics with a manL deletion mutant (SK36/manL) revealed redirection of pyruvate to production of acetate and formate, rather than lactate. These observations were consistent with measurements of decreased lactic acid accumulation and increased excretion of acetate, formate, pyruvate, and H2O2. Genes showing increased expression in SK36/manL included those encoding carbohydrate transporters, extracellular glycosidases, intracellular polysaccharide metabolism, and arginine deiminase and pathways for metabolism of acetoin, ethanolamine, ascorbate, and formate, along with genes required for membrane biosynthesis and adhesion. Streptococcus mutans UA159 persisted much better in biofilm cocultures with SK36/manL than with SK36, an effect that was further enhanced by culturing the biofilms anaerobically but dampened by adding arginine to the medium. We posited that the enhanced persistence of S. mutans with SK36/manL was in part due to excess excretion of pyruvate by the latter, as addition of pyruvate to S. mutans-S. sanguinis cocultures increased the proportions of UA159 in the biofilms. Reducing the buffer capacity or increasing the concentration of glucose benefited UA159 when cocultured with SK36, but not with SK36/manL, likely due to the altered metabolism and enhanced acid tolerance of the mutant. When manL was deleted in S. mutans or Streptococcus gordonii, the mutants presented altered fitness characteristics. Our study demonstrated that phosphotransferase system (PTS)-dependent modulation of central metabolism can profoundly affect streptococcal fitness and metabolic interactions, revealing another dimension in commensal-pathogen relationships influencing dental caries development. IMPORTANCE Dental caries is underpinned by a dysbiotic microbiome and increased acid production. As beneficial bacteria that can antagonize oral pathobionts, oral streptococci such as S. sanguinis and S. gordonii can ferment many carbohydrates, despite their relative sensitivity to low pH. We characterized the molecular basis for why mutants of glucose transporter ManLMNO of S. sanguinis showed enhanced production of hydrogen peroxide and ammonia and improved persistence under acidic conditions. A metabolic shift involving more than 300 genes required for carbohydrate transport, energy production, and envelope biogenesis was observed. Significantly, manL mutants engineered in three different oral streptococci displayed altered capacities for acid production and interspecies antagonism, highlighting the potential for targeting the glucose-PTS to modulate the pathogenicity of oral biofilms.

PRD-Containing Virulence Regulators (PCVRs) in Pathogenic Bacteria

Bacterial pathogens rely on a complex network of regulatory proteins to adapt to hostile and nutrient-limiting host environments. The phosphoenolpyruvate phosphotransferase system (PTS) is a conserved pathway in bacteria that couples transport of sugars with phosphorylation to monitor host carbohydrate availability. A family of structurally homologous PTS-regulatory-domain-containing virulence regulators (PCVRs) has been recognized in divergent bacterial pathogens, including Streptococcus pyogenes Mga and Bacillus anthracis AtxA. These paradigm PCVRs undergo phosphorylation, potentially via the PTS, which impacts their dimerization and their activity. Recent work with predicted PCVRs from Streptococcus pneumoniae (MgaSpn) and Enterococcus faecalis (MafR) suggest they interact with DNA like nucleoid-associating proteins. Yet, Mga binds to promoter sequences as a homo-dimeric transcription factor, suggesting a bi-modal interaction with DNA. High-resolution crystal structures of 3 PCVRs have validated the domain structure, but also raised additional questions such as how ubiquitous are PCVRs, is PTS-mediated histidine phosphorylation via potential PCVRs widespread, do specific sugars signal through PCVRs, and do PCVRs interact with DNA both as transcription factors and nucleoid-associating proteins? Here, we will review known and putative PCVRs based on key domain and functional characteristics and consider their roles as both transcription factors and possibly chromatin-structuring proteins.

Bacterial-induced pH shifts link individual cell physiology to macroscale collective behavior

Bacteria have evolved a diverse array of signaling pathways that enable them to quickly respond to environmental changes. Understanding how these pathways reflect environmental conditions and produce an orchestrated response is an ongoing challenge. Herein, we present a role for collective modifications of environmental pH carried out by microbial colonies living on a surface. We show that by collectively adjusting the local pH value, Paenibacillus spp., specifically, regulate their swarming motility. Moreover, we show that such pH-dependent regulation can converge with the carbon repression pathway to down-regulate flagellin expression and inhibit swarming in the presence of glucose. Interestingly, our results demonstrate that the observed glucose-dependent swarming repression is not mediated by the glucose molecule per se, as commonly thought to occur in carbon repression pathways, but rather is governed by a decrease in pH due to glucose metabolism. In fact, modification of the environmental pH by neighboring bacterial species could override this glucose-dependent repression and induce swarming of Paenibacillus spp. away from a glucose-rich area. Our results suggest that bacteria can use local pH modulations to reflect nutrient availability and link individual bacterial physiology to macroscale collective behavior.

Genome-wide analysis of in vivo CcpA binding with and without its key co-factor HPr in the major human pathogen group A Streptococcus

Catabolite control protein A (CcpA) is a master regulator of carbon source utilization and contributes to the virulence of numerous medically important Gram‐positive bacteria. Most functional assessments of CcpA, including interaction with its key co‐factor HPr, have been performed in nonpathogenic bacteria. In this study we aimed to identify the in vivo DNA binding profile of CcpA and assess the extent to which HPr is required for CcpA‐mediated regulation and DNA binding in the major human pathogen group A Streptococcus (GAS). Using a combination RNAseq/ChIP‐seq approach, we found that CcpA affects transcript levels of 514 of 1667 GAS genes (31%) whereas direct DNA binding was identified for 105 GAS genes. Three of the directly regulated genes encode the key GAS virulence factors Streptolysin S, PrtS (IL‐8 degrading proteinase), and SpeB (cysteine protease). Mutating CcpA Val301 to Ala (strain 2221‐CcpA‐V301A) abolished interaction between CcpA and HPr and impacted the transcript levels of 205 genes (40%) in the total CcpA regulon. By ChIP‐seq analysis, CcpAV301A bound to DNA from 74% of genes bound by wild‐type CcpA, but generally with lower affinity. These data delineate the direct CcpA regulon and clarify the HPr‐dependent and independent activities of CcpA in a key pathogenic bacterium.

Subpopulation behaviors in lactose metabolism by Streptococcus mutans

When Streptococcus mutans is transferred from a preferred carbohydrate (glucose or fructose) to lactose, initiation of growth can take several hours, and substantial amounts of glucose are released during growth. Here, S. mutans strains UA159 and GS-5 were examined for stochastic behaviors in transcription of the lac operon. Using a gfp reporter fusion, we demonstrated that induction of the lac operon occurs in only a fraction of the population, with prior exposure to carbohydrate source and strain influencing the magniture of the sub-population response. Lower glucokinase activity in GS-5 was associated with release of substantially more glucose than UA159 and significantly lower lac expression. Mutants unable to use lactose grew on lactose as the sole carbohydrate when strains with an intact lac operon were also present in the cultures, indicative of the potential for population cheating. Utilizing a set of engineered obligate cheating and non-cheating strains, we confirmed that cheating can sustain a heterogeneous population. Futher, obligate cheaters of GS-5 competed well with the non-cheaters and showed a high degree of competitive fitness in a human-derived consortium biofilm model. The results show that bet-hedging behaviors in carbohydrate metabolism may substantially influence the composition and pathogenic potential of oral biofilms.

Phosphotransferase System Uptake and Metabolism of the β-Glucoside Salicin Impact Group A Streptococcal Bloodstream Survival and Soft Tissue Infection

Streptococcus pyogenes (group A Streptococcus [GAS]), a major human-specific pathogen, relies on efficient nutrient acquisition for successful infection within its host. The phosphotransferase system (PTS) couples the import of carbohydrates with their phosphorylation prior to metabolism and has been linked to GAS pathogenesis. In a screen of an insertional mutant library of all 14 annotated PTS permease (EIIC) genes in MGAS5005, the annotated β-glucoside PTS transporter (bglP) was found to be crucial for GAS growth and survival in human blood and was validated in another M1T1 GAS strain, 5448. In 5448, bglP was shown to be in an operon with a putative phospho-β-glucosidase (bglB) downstream and a predicted antiterminator (licT) upstream. Using defined nonpolar mutants of the β-glucoside permease (bglP) and β-glucosidase enzyme (bglB) in 5448, we showed that bglB, not bglP, was important for growth in blood. Furthermore, transcription of the licT-blgPB operon was found to be repressed by glucose and induced by the β-glucoside salicin as the sole carbon source. Investigation of the individual bglP and bglB mutants determined that they influence in vitro growth in the β-glucoside salicin; however, only bglP was necessary for growth in other non-β-glucoside PTS sugars, such as fructose and mannose. Additionally, loss of BglP and BglB suggests that they are important for the regulation of virulence-related genes that control biofilm formation, streptolysin S (SLS)-mediated hemolysis, and localized ulcerative lesion progression during subcutaneous infections in mice. Thus, our results indicate that the β-glucoside PTS transports salicin and its metabolism can differentially influence GAS pathophysiology during soft tissue infection.

The local transcriptional regulators SacR1 and SacR2 act as repressors of fructooligosaccharides metabolism in Lactobacillus plantarum

Background

In Lactobacillus plantarum, fructooligosaccharides (FOS) metabolism is controlled by both global and local regulatory mechanisms. Although catabolite control protein A has been identified as a global regulator of FOS metabolism, the functions of local regulators remain unclear. This study aimed to elucidate the roles of two local regulators, SacR1 and SacR2, in the regulation of FOS metabolism in L. plantarum both in vitro and in vivo.

Results

The inactivation of sacR1 and sacR2 affected the growth and production of metabolites for strains grown on FOS or glucose, respectively. A reverse transcription-quantitative PCR analysis of one wild-type and two mutant strains (ΔsacR1 and ΔsacR2) of L. plantarum identified SacR1 and SacR2 as repressors of genes relevant to FOS metabolism in the absence of FOS, and these genes could be induced or derepressed by the addition of FOS. The analysis predicted four potential transcription factor binding sites (TFBSs) in the putative promoter regions of two FOS-related clusters. The binding of SacR1 and SacR2 to these TFBSs both in vitro and in vivo was verified using electrophoretic mobility shift assays and chromatin immunoprecipitation, respectively. A consensus sequence of WNNNNNAACGNNTTNNNNNW was deduced for the TFBSs of SacR1 and SacR2.

Conclusion

Our results identified SacR1 and SacR2 as local repressors for FOS metabolism in L. plantarum. The regulation is achieved by the binding of SacR1 and SacR2 to TFBSs in the promoter regions of FOS-related clusters. The results provide new insights into the complex network regulating oligosaccharide metabolism by lactic acid bacteria.

Influence of the phosphoenolpyruvate:carbohydrate phosphotransferase system on toxin gene expression and virulence in Bacillus anthracis

AtxA, the master virulence gene regulator of Bacillus anthracis, is a PRD-Containing Virulence Regulator (PCVR) as indicated by the crystal structure, post-translational modifications and activity of the protein. PCVRs are transcriptional regulators, named for PTS Regulatory Domains (PRDs) subject to phosphorylation by the phosphoenolpyruvate phosphotransferase system (PEP-PTS) and for their impact on virulence gene expression. Here we present data from experiments employing physiological, genetic and biochemical approaches that support a model in which the PTS proteins HPr and Enzyme I (EI) are required for transcription of the atxA gene, rather than phosphorylation of AtxA. We show that atxA transcription is reduced 2.5-fold in a mutant lacking HPr and EI, and that this change is sufficient to affect anthrax toxin production. Mutants harboring HPr proteins altered for phosphotransfer activity were unable to restore atxA transcription to parent levels, suggesting that phosphotransfer activity of HPr and EI is important for regulation of atxA. In a mouse model for anthrax, a HPr^- EI^- mutant was attenuated for virulence. Virulence was restored by expressing atxA from an alternative, PTS-independent, promoter. Our data support a model in which HPr transfers a phosphate to an unidentified downstream transcriptional regulator to influence atxA gene transcription.

Regulation of the β-hemolysin gene cluster of Streptococcus anginosus by CcpA

Streptococcus anginosus is increasingly recognized as an opportunistic pathogen. However, our knowledge about virulence determinants in this species is scarce. One exception is the streptolysin-S (SLS) homologue responsible for the β-hemolytic phenotype of the S. anginosus type strain. In S. anginosus the expression of the hemolysin is reduced in the presence of high glucose concentrations. To investigate the genetic mechanism of the hemolysin repression we created an isogenic ccpA deletion strain. In contrast to the wild type strain, this mutant exhibits hemolytic activity in presence of up to 25 mM glucose supplementation, a phenotype that could be reverted by ccpA complementation. To further demonstrate that CcpA directly regulates the hemolysin expression, we performed an in silico analysis of the promoter of the SLS gene cluster and we verified the binding of CcpA to the promoter by electrophoretic mobility shift assays. This allowed us to define the CcpA binding site in the SLS promoter region of S. anginosus. In conclusion, we report for the first time the characterization of a potential virulence regulator in S. anginosus.

CcpA-Dependent Carbon Catabolite Repression Regulates Fructooligosaccharides Metabolism in Lactobacillus plantarum

Fructooligosaccharides (FOSs) metabolism in Lactobacillus plantarum is controlled by two gene clusters, and the global regulator catabolite control protein A (CcpA) may be involved in the regulation. To understand the mechanism, this study focused on the regulation relationships of CcpA toward target genes and the binding effects on the catabolite responsive element (cre). First, reverse transcription-PCR analysis of the transcriptional organization of the FOS-related gene clusters showed that they were organized in three independent polycistronic units. Diauxic growth, hierarchical utilization of carbohydrates and repression of FOS-related genes were observed in cultures containing FOS and glucose, suggesting carbon catabolite repression (CCR) control in FOS utilization. Knockout of ccpA gene eliminated these phenomena, indicating the principal role of this gene in CCR of FOS metabolism. Furthermore, six potential cre sites for CcpA binding were predicted in the regions of putative promoters of the two clusters. Direct binding was confirmed by electrophoretic mobility shift assays in vitro and chromatin immunoprecipitation in vivo. The results of the above studies suggest that CcpA is a vital regulator of FOS metabolism in L. plantarum and that CcpA-dependent CCR regulates FOS metabolism through the direct binding of CcpA toward the cre sites in the promoter regions of FOS-related clusters.

Glucose Levels Alter the Mga Virulence Regulon in the Group A Streptococcus

Many bacterial pathogens coordinately regulate genes encoding important metabolic pathways during disease progression, including the phosphoenolpyruvate (PEP)-phosphotransferase system (PTS) for uptake of carbohydrates. The Gram-positive Group A Streptococcus (GAS) is a pathogen that infects multiple tissues in the human host. The virulence regulator Mga in GAS can be phosphorylated by the PTS, affecting Mga activity based on carbohydrate availability. Here, we explored the effects of glucose availability on the Mga regulon. RNA-seq was used to identify transcriptomic differences between the Mga regulon grown to late log phase in the presence of glucose (THY) or after glucose has been expended (C media). Our results revealed a correlation between the genes activated in C media with those known to be repressed by CcpA, indicating that C media mimics a non-preferred sugar environment. Interestingly, we found very little overlap in the Mga regulon from GAS grown in THY versus C media beyond the core virulence genes. We also observed an alteration in the phosphorylation status of Mga, indicating that the observed media differences in the Mga regulon may be directly attributed to glucose levels. Thus, these results support an in vivo link between glucose availability and virulence regulation in GAS.

Antimicrobial and Antibiofilm Activity of Human Milk Oligosaccharides against Streptococcus agalactiae, Staphylococcus aureus, and Acinetobacter baumannii

In a previous study, we reported that human milk oligosaccharides (HMOs) isolated from five donor milk samples possessed antimicrobial and antibiofilm activity against Streptococcus agalactiae, also known as Group B Streptococcus or GBS. Herein, we present a broader evaluation of the antimicrobial and antibiofilm activity by screening HMOs from 14 new donors against three strains of GBS and two of the ESKAPE pathogens of particular interest to child health, Staphylococcus aureus and Acinetobacter baumannii. Growth and biofilm assays showed that HMOs from these new donors possessed antimicrobial and antibiofilm activity against all three strains of GBS, antibiofilm activity against methicillin-resistant S. aureus strain USA300, and antimicrobial activity against A. baumannii strain ATCC 19606.

A Flexible Binding Site Architecture Provides New Insights into CcpA Global Regulation in Gram-Positive Bacteria

Catabolite control protein A (CcpA) is the master regulator in Gram-positive bacteria that mediates carbon catabolite repression (CCR) and carbon catabolite activation (CCA), two fundamental regulatory mechanisms that enable competitive advantages in carbon catabolism. It is generally regarded that CcpA exerts its regulatory role by binding to a typical 14- to 16-nucleotide (nt) consensus site that is called a catabolite response element (cre) within the target regions. However, here we report a previously unknown noncanonical flexible architecture of the CcpA-binding site in solventogenic clostridia, providing new mechanistic insights into catabolite regulation. This novel CcpA-binding site, named cre_var, has a unique architecture that consists of two inverted repeats and an intervening spacer, all of which are variable in nucleotide composition and length, except for a 6-bp core palindromic sequence (TGTAAA/TTTACA). It was found that the length of the intervening spacer of cre_var can affect CcpA binding affinity, and moreover, the core palindromic sequence of cre_var is the key structure for regulation. Such a variable architecture of cre_var shows potential importance for CcpA’s diverse and fine regulation. A total of 103 potential cre_var sites were discovered in solventogenic Clostridium acetobutylicum, of which 42 sites were picked out for electrophoretic mobility shift assays (EMSAs), and 30 sites were confirmed to be bound by CcpA. These 30 cre_var sites are associated with 27 genes involved in many important pathways. Also of significance, the cre_var sites are found to be widespread and function in a great number of taxonomically different Gram-positive bacteria, including pathogens, suggesting their global role in Gram-positive bacteria.

In Gram-positive bacteria, the global regulator CcpA controls a large number of important physiological and metabolic processes. Although a typical consensus CcpA-binding site, cre, has been identified, it remains poorly explored for the diversity of CcpA-mediated catabolite regulation. Here, we discovered a novel flexible CcpA-binding site architecture (cre_var) that is highly variable in both length and base composition but follows certain principles, providing new insights into how CcpA can differentially recognize a variety of target genes to form a complicated regulatory network. A comprehensive search further revealed the wide distribution of cre_var sites in Gram-positive bacteria, indicating it may have a universal function. This finding is the first to characterize such a highly flexible transcription factor-binding site architecture, which would be valuable for deeper understanding of CcpA-mediated global catabolite regulation in bacteria.

A Multi-Serotype Approach Clarifies the Catabolite Control Protein A Regulon in the Major Human Pathogen Group A Streptococcus

Catabolite control protein A (CcpA) is a highly conserved, master regulator of carbon source utilization in gram-positive bacteria, but the CcpA regulon remains ill-defined. In this study we aimed to clarify the CcpA regulon by determining the impact of CcpA-inactivation on the virulence and transcriptome of three distinct serotypes of the major human pathogen Group A Streptococcus (GAS). CcpA-inactivation significantly decreased GAS virulence in a broad array of animal challenge models consistent with the idea that CcpA is critical to gram-positive bacterial pathogenesis. Via comparative transcriptomics, we established that the GAS CcpA core regulon is enriched for highly conserved CcpA binding motifs (i.e. cre sites). Conversely, strain-specific differences in the CcpA transcriptome seems to consist primarily of affected secondary networks. Refinement of cre site composition via analysis of the core regulon facilitated development of a modified cre consensus that shows promise for improved prediction of CcpA targets in other medically relevant gram-positive pathogens.

Metabolic traits of pathogenic streptococci

Invasive and noninvasive diseases caused by facultative pathogenic streptococci depend on their equipment with virulence factors and on their ability to sense and adapt to changing nutrients in different host environments. The knowledge of the principal metabolic mechanisms which allow these bacteria to recognize and utilize nutrients in host habitats is a prerequisite for our understanding of streptococcal pathogenicity and the development of novel control strategies. This review aims to summarize and compare the central carbohydrate metabolic and amino acid biosynthetic pathways of a selected group of streptococcal species, all belonging to the naso-oropharyngeal microbiome in humans and/or animals. We also discuss the urgent need of comprehensive metabolomics approaches for a better understanding of the streptococcal metabolism during host-pathogen interaction.

Lactobacilli Interfere with Streptococcus pyogenes Hemolytic Activity and Adherence to Host Epithelial Cells

Streptococcus pyogenes [Group A streptococcus (GAS)], a frequent colonizer of the respiratory tract mucosal surface, causes a variety of human diseases, ranging from pharyngitis to the life-threatening streptococcal toxic shock-like syndrome. Lactobacilli have been demonstrated to colonize the respiratory tract. In this study, we investigated the interference of lactobacilli with the virulence phenotypes of GAS. The Lactobacillus strains L. rhamnosus Kx151A1 and L. reuteri PTA-5289, but not L. salivarius LMG9477, inhibited the hemolytic activity of S. pyogenes S165. The inhibition of hemolytic activity was attributed to a decrease in the production of streptolysin S (SLS). Conditioned medium (CM) from the growth of L. rhamnosus Kx151A1 and L. reuteri PTA-5289 was sufficient to down-regulate the expression of the sag operon, encoding SLS. The Lactobacillus strains L. rhamnosus Kx151A1, L. reuteri PTA-5289, and L. salivarius LMG9477 inhibited the initial adherence of GAS to host epithelial cells. Intriguingly, competition with a combination of Lactobacillus species reduced GAS adherence to host cells most efficiently. The data suggest that an effector molecule released from certain Lactobacillus strains attenuates the production of SLS at the transcriptional level and that combinations of Lactobacillus strains may protect the pharyngeal mucosa more efficiently from the initial colonization of GAS. The effector molecules released from Lactobacillus strains affecting the virulence phenotypes of pathogens hold potential in the development of a new generation of therapeutics.

The roles of RelA/(p)ppGpp in glucose-starvation induced adaptive response in the zoonotic Streptococcus suis

The (p)ppGpp signal molecules play a central role in the stringent response (SR) to adapt to nutrient starvation in bacteria, yet the carbohydrate starvation induced adaptive response and the roles of SR in this response is not well characterized, especially in Gram-positives. Here, two (p)ppGpp synthetases RelA and RelQ are identified in Streptococcus suis, an important emerging zoonotic Gram-positive bacterium, while only RelA is functional under glucose starvation. To characterize the roles of RelA/(p)ppGpp in glucose starvation response in S. suis, the growth curves and transcriptional profiles were compared between the mutant strain ΔrelA [a (p)ppGpp⁰ strain under glucose starvation] and its parental strain SC-19 [(p)ppGpp⁺]. The results showed great difference between SC-19 and ΔrelA on adaptive responses when suffering glucose starvation, and demonstrated that RelA/(p)ppGpp plays important roles in adaptation to glucose starvation. Besides the classic SR including inhibition of growth and related macromolecular synthesis, the extended adaptive response also includes inhibited glycolysis, and carbon catabolite repression (CCR)-mediated carbohydrate-dependent metabolic switches. Collectively, the pheno- and genotypic characterization of the glucose starvation induced adaptive response in S. suis makes a great contribution to understanding better the mechanism of SR.

The essential genome of Streptococcus agalactiae

BACKGROUND

Next-generation sequencing of transposon-genome junctions from a saturated bacterial mutant library (Tn-seq) is a powerful tool that permits genome-wide determination of the contribution of genes to fitness of the organism under a wide range of experimental conditions. We report development, testing, and results from a Tn-seq system for use in Streptococcus agalactiae (group B Streptococcus; GBS), an important cause of neonatal sepsis.

METHODS

Our method uses a Himar1 mini-transposon that inserts at genomic TA dinucleotide sites, delivered to GBS on a temperature-sensitive plasmid that is subsequently cured from the bacterial population. In order to establish the GBS essential genome, we performed Tn-seq on DNA collected from three independent mutant libraries-with at least 135,000 mutants per library-at serial 24 h time points after outgrowth in rich media.

RESULTS

After statistical analysis of transposon insertion density and distribution, we identified 13.5 % of genes as essential and 1.2 % as critical, with high levels of reproducibility. Essential and critical genes are enriched for fundamental cellular housekeeping functions, such as acyl-tRNA biosynthesis, nucleotide metabolism, and glycolysis. We further validated our system by comparing fitness assignments of homologous genes in GBS and a close bacterial relative, Streptococcus pyogenes, which demonstrated 93 % concordance. Finally, we used our fitness assignments to identify signal transduction pathway components predicted to be essential or critical in GBS.

CONCLUSIONS

We believe that our baseline fitness assignments will be a valuable tool for GBS researchers and that our system has the potential to reveal key pathogenesis gene networks and potential therapeutic/preventative targets.

Regulating the Intersection of Metabolism and Pathogenesis in Gram-positive Bacteria

Pathogenic bacteria must contend with immune systems that actively restrict the availability of nutrients and cofactors, and create a hostile growth environment. To deal with these hostile environments, pathogenic bacteria have evolved or acquired virulence determinants that aid in the acquisition of nutrients. This connection between pathogenesis and nutrition may explain why regulators of metabolism in nonpathogenic bacteria are used by pathogenic bacteria to regulate both metabolism and virulence. Such coordinated regulation is presumably advantageous because it conserves carbon and energy by aligning synthesis of virulence determinants with the nutritional environment. In Gram-positive bacterial pathogens, at least three metabolite-responsive global regulators, CcpA, CodY, and Rex, have been shown to coordinate the expression of metabolism and virulence genes. In this chapter, we discuss how environmental challenges alter metabolism, the regulators that respond to this altered metabolism, and how these regulators influence the host-pathogen interaction.

Induction of a quorum sensing pathway by environmental signals enhances group A streptococcal resistance to lysozyme

The human-restricted pathogen Streptococcus pyogenes (Group A Streptococcus, GAS) is responsible for wide-ranging pathologies at numerous sites in the body but has the proclivity to proliferate in individuals asymptomatically. The ability to survive in diverse tissues is undoubtedly benefited by sensory pathways that recognize environmental cues corresponding to stress and nutrient availability and thereby trigger adaptive responses. We investigated the impact that environmental signals contribute to cell-to-cell chemical communication [quorum sensing (QS)] by monitoring activity of the Rgg2/Rgg3 and SHP-pheromone system in GAS. We identified metal limitation and the alternate carbon source mannose as two environmental indicators likely to be encountered by GAS in the host that significantly induced the Rgg-SHP system. Disruption of the metal regulator MtsR partially accounted for the response to metal depletion, whereas ptsABCD was primarily responsible for QS induction due to mannose, but each sensory system induced Rgg-SHP signaling apparently by different mechanisms. Significantly, we found that induction of QS, regardless of the GAS serotype tested, led to enhanced resistance to the antimicrobial agent lysozyme. These results indicate the benefits for GAS to integrate environmental signals with intercellular communication pathways in protection from host defenses.

Essential Genes in the Core Genome of the Human Pathogen Streptococcus pyogenes

Streptococcus pyogenes (Group A Streptococcus, GAS) remains a major public health burden worldwide, infecting over 750 million people leading to over 500,000 deaths annually. GAS pathogenesis is complex, involving genetically distinct GAS strains and multiple infection sites. To overcome fastidious genetic manipulations and accelerate pathogenesis investigations in GAS, we developed a mariner-based system (Krmit) for en masse monitoring of complex mutant pools by transposon sequencing (Tn-seq). Highly saturated transposant libraries (Krmit insertions in ca. every 25 nucleotides) were generated in two distinct GAS clinical isolates, a serotype M1T1 invasive strain 5448 and a nephritogenic serotype M49 strain NZ131, and analyzed using a Bayesian statistical model to predict GAS essential genes, identifying sets of 227 and 241 of those genes in 5448 and NZ131, respectively. A large proportion of GAS essential genes corresponded to key cellular processes and metabolic pathways, and 177 were found conserved within the GAS core genome established from 20 available GAS genomes. Selected essential genes were validated using conditional-expression mutants. Finally, comparison to previous essentiality analyses in S. sanguinis and S. pneumoniae revealed significant overlaps, providing valuable insights for the development of new antimicrobials to treat infections by GAS and other pathogenic streptococci.

The bacterial phosphoenolpyruvate:carbohydrate phosphotransferase system: regulation by protein phosphorylation and phosphorylation-dependent protein-protein interactions

The bacterial phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS) carries out both catalytic and regulatory functions. It catalyzes the transport and phosphorylation of a variety of sugars and sugar derivatives but also carries out numerous regulatory functions related to carbon, nitrogen, and phosphate metabolism, to chemotaxis, to potassium transport, and to the virulence of certain pathogens. For these different regulatory processes, the signal is provided by the phosphorylation state of the PTS components, which varies according to the availability of PTS substrates and the metabolic state of the cell. PEP acts as phosphoryl donor for enzyme I (EI), which, together with HPr and one of several EIIA and EIIB pairs, forms a phosphorylation cascade which allows phosphorylation of the cognate carbohydrate bound to the membrane-spanning EIIC. HPr of firmicutes and numerous proteobacteria is also phosphorylated in an ATP-dependent reaction catalyzed by the bifunctional HPr kinase/phosphorylase. PTS-mediated regulatory mechanisms are based either on direct phosphorylation of the target protein or on phosphorylation-dependent interactions. For regulation by PTS-mediated phosphorylation, the target proteins either acquired a PTS domain by fusing it to their N or C termini or integrated a specific, conserved PTS regulation domain (PRD) or, alternatively, developed their own specific sites for PTS-mediated phosphorylation. Protein-protein interactions can occur with either phosphorylated or unphosphorylated PTS components and can either stimulate or inhibit the function of the target proteins. This large variety of signal transduction mechanisms allows the PTS to regulate numerous proteins and to form a vast regulatory network responding to the phosphorylation state of various PTS components.

Streptococcus pyogenes biofilms-formation, biology, and clinical relevance

Streptococcus pyogenes (group A streptococci, GAS) is an exclusive human bacterial pathogen. The virulence potential of this species is tremendous. Interactions with humans range from asymptomatic carriage over mild and superficial infections of skin and mucosal membranes up to systemic purulent toxic-invasive disease manifestations. Particularly the latter are a severe threat for predisposed patients and lead to significant death tolls worldwide. This places GAS among the most important Gram-positive bacterial pathogens. Many recent reviews have highlighted the GAS repertoire of virulence factors, regulators and regulatory circuits/networks that enable GAS to colonize the host and to deal with all levels of the host immune defense. This covers in vitro and in vivo studies, including animal infection studies based on mice and more relevant, macaque monkeys. It is now appreciated that GAS, like many other bacterial species, do not necessarily exclusively live in a planktonic lifestyle. GAS is capable of microcolony and biofilm formation on host cells and tissues. We are now beginning to understand that this feature significantly contributes to GAS pathogenesis. In this review we will discuss the current knowledge on GAS biofilm formation, the biofilm-phenotype associated virulence factors, regulatory aspects of biofilm formation, the clinical relevance, and finally contemporary treatment regimens and future treatment options.

Fueling the caries process: carbohydrate metabolism and gene regulation by Streptococcus mutans

The nature of the oral cavity and host behaviors has mandated that the oral microbiota evolve mechanisms for coping with environmental fluctuations, especially changes in the type and availability of carbohydrates. In the case of human dental caries, the presence of excess carbohydrates is often responsible for altering the local environment to be more favorable for species associated with the initiation and progression of disease, including Streptococcus mutans. Some of the earliest endeavors to understand how cariogenic species respond to environmental perturbations were carried out using chemostat cultivation, which provides fine control over culture conditions and bacterial behaviors. The development of genome-scale methodologies has allowed for the combination of sophisticated cultivation technologies with genome-level analysis to more thoroughly probe how bacterial pathogens respond to environmental stimuli. Recent investigations in S. mutans and other closely related streptococci have begun to reveal that carbohydrate metabolism can drastically impact pathogenic potential and highlight the important influence that nutrient acquisition has on the success of pathogens; inside and outside of the oral cavity. Collectively, research into pathogenic streptococci, which have evolved in close association with the human host, has begun to unveil the essential nature of careful orchestration of carbohydrate acquisition and catabolism to allow the organisms to persist and, when conditions allow, initiate or worsen disease.

To harm or not to harm? On the evolution and expression of virulence in group A streptococci

Group A streptococci (GAS) cause three different types of infection (sensu lato) with distinct levels of virulence: asymptomatic colonization, superficial symptomatic infection, and invasive infection. To address why this pattern with several infection types has evolved, we combine mechanistic understanding from infection medicine with recent theory from evolutionary ecology. We propose that asymptomatic colonization and superficial symptomatic infection exploit different states of the host epithelium to maximize transmission between hosts in different epidemiological conditions, whereas the ability of the bacteria to cause invasive infection is a non-adaptive side effect of traits required for superficial symptomatic infection.

Regulation of pqs quorum sensing via catabolite repression control in Pseudomonas aeruginosa

Bacteria have evolved a set of regulatory pathways to adapt to the dynamic nutritional environment during the course of infection. However, the underlying mechanism of the regulatory effects by nutritional cues on bacterial pathogenesis is unclear. In the present study, we showed that the Pseudomonas aeruginosa catabolite repression control protein regulates the Pseudomonas quinolone signal quorum sensing, which further controls synthesis of virulence factor pyocyanin, biofilm formation and survival during infection models. Our study suggests that deregulation of the catabolite repression by P. aeruginosa might enhance its fitness during cystic fibrosis infections.

LacR mutations are frequently observed in Streptococcus intermedius and are responsible for increased intermedilysin production and virulence

Streptococcus intermedius secretes a human-specific cytolysin, intermedilysin (ILY), which is considered to be the major virulence factor of this pathogen. We screened for a repressor of ily expression by using random gene disruption in a low-ILY-producing strain (PC574). Three independent high-ILY-producing colonies that had plasmid insertions within a gene that has high homology to lacR were isolated. Validation of these observations was achieved through disruption of lacR in strain PC574 with an erythromycin cassette, which also led to higher hemolytic activity, increased transcription of ily, and higher cytotoxicity against HepG2 cells, compared to the parental strain. The direct binding of LacR within the ily promoter region was shown by a biotinylated DNA probe pulldown assay, and the amount of ILY secreted into the culture supernatant by PC574 cells was increased by adding lactose or galactose to the medium as a carbon source. Furthermore, we examined lacR nucleotide sequences and the hemolytic activity of 50 strains isolated from clinical infections and 7 strains isolated from dental plaque. Of the 50 strains isolated from infections, 13 showed high ILY production, 11 of these 13 strains had one or more point mutations and/or an insertion mutation in LacR, and almost all mutations were associated with a marked decline in LacR function. These results strongly suggest that mutation in lacR is required for the overproduction of ILY, which is associated with an increase in pathogenicity of S. intermedius.

PTS phosphorylation of Mga modulates regulon expression and virulence in the group A streptococcus

The ability of a bacterial pathogen to monitor available carbon sources in host tissues provides a clear fitness advantage. In the group A streptococcus (GAS), the virulence regulator Mga contains homology to phosphotransferase system (PTS) regulatory domains (PRDs) found in sugar operon regulators. Here we show that Mga was phosphorylated in vitro by the PTS components EI/HPr at conserved PRD histidines. A ΔptsI (EI-deficient) GAS mutant exhibited decreased Mga activity. However, PTS-mediated phosphorylation inhibited Mga-dependent transcription of emm in vitro. Using alanine (unphosphorylated) and aspartate (phosphomimetic) mutations of PRD histidines, we establish that a doubly phosphorylated PRD1 phosphomimetic (D/DMga4) is completely inactive in vivo, shutting down expression of the Mga regulon. Although D/DMga4 is still able to bind DNA in vitro, homo-multimerization of Mga is disrupted and the protein is unable to activate transcription. PTS-mediated regulation of Mga activity appears to be important for pathogenesis, as bacteria expressing either non-phosphorylated (A/A) or phosphomimetic (D/D) PRD1 Mga mutants were attenuated in a model of GAS invasive skin disease. Thus, PTS-mediated phosphorylation of Mga may allow the bacteria to modulate virulence gene expression in response to carbohydrate status. Furthermore, PRD-containing virulence regulators (PCVRs) appear to be widespread in Gram-positive pathogens.

Adaptive response of Group B streptococcus to high glucose conditions: new insights on the CovRS regulation network

Although the contribution of carbohydrate catabolism to bacterial colonization and infection is well recognized, the transcriptional changes during these processes are still unknown. In this study, we have performed comparative global gene expression analysis of GBS in sugar-free versus high glucose milieu. The analysis revealed a differential expression of genes involved in metabolism, transport and host-pathogen interaction. Many of them appeared to be among the genes previously reported to be controlled by the CovRS two-component system. Indeed, the transcription profile of a ΔcovRS strain grown in high-glucose conditions was profoundly affected. In particular, of the total genes described to be regulated by glucose, ∼27% were under CovRS control with a functional role in protein synthesis, transport, energy metabolism and regulation. Among the CovRS dependent genes, we found bibA, a recently characterized adhesin involved in bacterial serum resistance and here reported to be down-regulated by glucose. ChIP analysis revealed that in the presence of glucose, CovR binds bibA promoter in vivo, suggesting that CovR may act as a negative regulator or a repressor. We also demonstrated that, as for other target promoters, chemical phosphorylation of CovR in aspartic acid increases its affinity for the bibA promoter region. The data reported in this study contribute to the understanding of the molecular mechanisms modulating the adaptation of GBS to glucose.

Catabolite control protein A of Streptococcus suis type 2 contributes to sugar metabolism and virulence

Catabolite control protein A (CcpA) is the major transcriptional regulator in carbon catabolite repression in several Gram-positive bacteria. We attempted to characterize the role of a CcpA homologue of Streptococcus suis type 2 in sugar metabolism and virulence. Addition of glucose or sucrose to the defined medium significantly reduced the activity of raffinose-inducible α-galactosidase, cellobiose-inducible β-glucosidase, and maltose-inducible α-glucosidase of the wild-type strain by about 9, 4, and 2-3 fold, respectively. Deletion of ccpA substantially derepressed the effects of repressing sugars on α-galactosidase or β-glucosidase activity. The ccpA deletion mutant showed reduced expression of virulence genes sly and eno (P<0.05), decreased adhesion to and invasion into endothelial cells (P<0.05), and attenuated virulence to mice with significant reduction of death rate and bacterial burden in organs, as compared to the wild-type strain. Both the in vitro and in vivo defect phenotypes were reversible by ccpA complementation. Thus, this study shows that CcpA of S. suis type 2 plays an important role in carbon catabolite repression and virulence.

Nucleotides critical for the interaction of the Streptococcus pyogenes Mga virulence regulator with Mga-regulated promoter sequences

The Mga regulator of Streptococcus pyogenes directly activates the transcription of a core regulon that encodes virulence factors such as M protein (emm), C5a peptidase (scpA), and streptococcal inhibitor of complement (sic) by directly binding to a 45-bp binding site as determined by an electrophoretic mobility shift assay (EMSA) and DNase I protection. However, by comparing the nucleotide sequences of all established Mga binding sites, we found that they exhibit only 13.4% identity with no discernible symmetry. To determine the core nucleotides involved in functional Mga-DNA interactions, the M1T1 Pemm1 binding site was altered and screened for nucleotides important for DNA binding in vitro and for transcriptional activation using a plasmid-based luciferase reporter in vivo. Following this analysis, 34 nucleotides within the Pemm1 binding site that had an effect on Mga binding, Mga-dependent transcriptional activation, or both were identified. Of these critical nucleotides, guanines and cytosines within the major groove were disproportionately identified clustered at the 5' and 3' ends of the binding site and with runs of nonessential adenines between the critical nucleotides. On the basis of these results, a Pemm1 minimal binding site of 35 bp bound Mga at a level comparable to the level of binding of the larger 45-bp site. Comparison of Pemm with directed mutagenesis performed in the M1T1 Mga-regulated PscpA and Psic promoters, as well as methylation interference analysis of PscpA, establish that Mga binds to DNA in a promoter-specific manner.

cis-Acting elements that control expression of the master virulence regulatory gene atxA in Bacillus anthracis

Transcription of the Bacillus anthracis structural genes for the anthrax toxin proteins and biosynthetic operon for capsule is positively regulated by AtxA, a transcription regulator with unique properties. Consistent with the role of atxA in virulence factor expression, a B. anthracis atxA-null mutant is avirulent in a murine model for anthrax. In culture, multiple signals impact atxA transcript levels, and the timing and steady-state level of atxA expression are critical for optimal toxin and capsule synthesis. Despite the apparent complex control of atxA transcription, only one trans-acting protein, the transition state regulator AbrB, has been demonstrated to interact directly with the atxA promoter. Here we employ 5' and 3' deletion analysis and site-directed mutagenesis of the atxA control region to demonstrate that atxA transcription from the major start site P1 is dependent upon a consensus sequence for the housekeeping sigma factor SigA and an A+T-rich upstream element for RNA polymerase. We also show that an additional trans-acting protein(s) binds specifically to atxA promoter sequences located between -13 and +36 relative to P1 and negatively impacts transcription. Deletion of this region increases promoter activity up to 15-fold. Site-directed mutagenesis of a 9-bp palindromic sequence within the region prevents binding of the trans-acting protein(s), increasing promoter activity 7-fold and resulting in a corresponding increase in AtxA and anthrax toxin production. Notably, an atxA promoter mutant that produced elevated levels of AtxA and toxin proteins during culture was unaffected for virulence in a murine model for anthrax.

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.

CcpA-dependent carbohydrate catabolite repression regulates galactose metabolism in Streptococcus oligofermentans

Streptococcus oligofermentans is an oral commensal that inhibits the growth of the caries pathogen Streptococcus mutans by producing copious amounts of H(2)O(2) and that grows faster than S. mutans on galactose. In this study, we identified a novel eight-gene galactose (gal) operon in S. oligofermentans that was comprised of lacABCD, lacX, and three genes encoding a galactose-specific transporter. Disruption of lacA caused more growth reduction on galactose than mutation of galK, a gene in the Leloir pathway, indicating that the principal role of this operon is in galactose metabolism. Diauxic growth was observed in cultures containing glucose and galactose, and a luciferase reporter fusion to the putative gal promoter demonstrated 12-fold repression of the operon expression by glucose but was induced by galactose, suggesting a carbon catabolite repression (CCR) control in galactose utilization. Interestingly, none of the single-gene mutations in the well-known CCR regulators ccpA and manL affected diauxic growth, although the operon expression was upregulated in these mutants in glucose. A double mutation of ccpA and manL eliminated glucose repression of galactose utilization, suggesting that these genes have parallel functions in regulating gal operon expression and mediating CCR. Electrophoretic mobility shift assays demonstrated binding of CcpA to the putative catabolite response element motif in the promoter regions of the gal operon and manL, suggesting that CcpA regulates CCR through direct regulation of the transcription of the gal operon and manL. This provides the first example of oral streptococci using two parallel CcpA-dependent CCR pathways in controlling carbohydrate metabolism.

Common regulators of virulence in streptococci

Streptococcal species are a diverse group of bacteria which can be found in animals and humans. Their interactions with host organisms can vary from commensal to pathogenic. Many of the pathogenic species are causative agents of severe, invasive infections in their hosts, accounting for a high burden of morbidity and mortality, associated with high economic costs in industry and health care. Among them, Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus pneumoniae, and Streptococcus suis are discussed here. An environmentally stimulated and tightly controlled expression of their virulence factors is of utmost importance for their pathogenic potential. Thus, the most universal and widespread regulators from the classes of stand-alone transcriptional regulators, two-component signal transduction systems (TCS), eukaryotic-like serine/threonine kinases, and small noncoding RNAs are the topic of this chapter. The regulatory levels are reviewed with respect to function, activity, and their role in pathogenesis. Understanding of and interfering with transcriptional regulation mechanisms and networks is a promising basis for the development of novel anti-infective therapies.

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.

Surface export of GAPDH/SDH, a glycolytic enzyme, is essential for Streptococcus pyogenes virulence

Streptococcal surface dehydrogenase (SDH) (glyceraldehyde-3-phosphate dehydrogenase [GAPDH]) is an anchorless major multifunctional surface protein in group A Streptococcus (GAS) with the ability to bind important mammalian proteins, including plasmin(ogen). Although several biological properties of SDH are suggestive of its possible role in GAS virulence, its direct role in GAS pathogenesis has not been ascertained because it is essential for GAS survival. Thus, it has remained enigmatic as to “how and why” SDH/GAPDH is exported onto the bacterial surface. The present investigation highlights “why” SDH is exported onto the GAS surface. Differential microarray-based genome-wide transcript abundance analysis was carried out using a specific mutant, which was created by inserting a hydrophobic tail at the C-terminal end of SDH (M1-SDH_HBtail) and thus preventing its exportation onto the GAS surface. This analysis revealed downregulation of the majority of genes involved in GAS virulence and genes belonging to carbohydrate and amino acid metabolism and upregulation of those related to lipid metabolism. The complete attenuation of this mutant for virulence in the mouse model and the decreased and increased virulence of the wild-type and mutant strains postcomplementation with SDH_HBtail and SDH, respectively, indicated that the SDH surface export indeed regulates GAS virulence. M1-SDH_HBtail also displayed unaltered growth patterns, increased intracellular ATP concentration and Hpr double phosphorylation, and significantly reduced pH tolerance, streptolysin S, and SpeB activities. These phenotypic and physiological changes observed in the mutant despite the unaltered expression levels of established transcriptional regulators further highlight the fact that SDH interfaces with many regulators and its surface exportation is essential for GAS virulence.

Streptococcal surface dehydrogenase (SDH), a classical anchorless cytoplasmically localized glycolytic enzyme, is exported onto the group A Streptococcus (GAS) surface through a hitherto unknown mechanism(s). It has not been known why GAS or other prokaryotes should export this protein onto the surface. By genetic manipulations, we created a novel GAS mutant strain expressing SDH with a 12-amino-acid hydrophobic tail at its C-terminal end and thus were able to prevent its surface exportation without altering its enzymatic activity or growth pattern. Interestingly, the mutant was completely attenuated for virulence in a mouse peritonitis model. The global gene expression profiles of this mutant reveal that the surface exportation of SDH is mandatory to maintain GAS virulence. The ability of GAS as a successful pathogen to localize SDH in the cytoplasm as well as on the surface is physiologically relevant and dynamically obligatory to fine-tune the functions of many transcriptional regulators and also to exploit its virulence properties for infection.

Mutational analysis of glucose transport regulation and glucose-mediated virulence gene repression in Listeria monocytogenes

Listeria monocytogenes transports glucose/mannose via non-PTS permeases and phosphoenolpyruvate:carbohydrate phosphotransferase systems (PTS). Two mannose class PTS are encoded by the constitutively expressed mpoABCD and the inducible manLMN operons. The man operon encodes the main glucose transporter because manL or manM deletion significantly slows glucose utilization, whereas mpoA deletion has no effect. The PTS(Mpo) mainly functions as a constitutively synthesized glucose sensor controlling man operon expression by phosphorylating and interacting with ManR, a LevR-like transcription activator. EIIB(Mpo) plays a dual role in ManR regulation: P~EIIB(Mpo) prevailing in the absence of glucose phosphorylates and thereby inhibits ManR activity, whereas unphosphorylated EIIB(Mpo) prevailing during glucose uptake is needed to render ManR active. In contrast to mpoA, deletion of mpoB therefore strongly inhibits man operon expression and glucose consumption. A ΔptsI (EI) mutant consumes glucose at an even slower rate probably via GlcU-like non-PTS transporters. Interestingly, deletion of ptsI, manL, manM or mpoB causes elevated PrfA-mediated virulence gene expression. The PTS(Man) is the major player in glucose-mediated PrfA inhibition because the ΔmpoA mutant showed normal PrfA activity. The four mutants showing PrfA derepression contain no or only little unphosphorylated EIIAB(Man) (ManL), which probably plays a central role in glucose-mediated PrfA regulation.