Mry, a trans-acting positive regulator of the M protein gene of Streptococcus pyogenes with similarity to the receptor proteins of two-component regulatory systems

Activation of the SMU.1882 transcription by CovR in Streptococcus mutans

In Streptococcus mutans, the global response regulator CovR plays an important role in biofilm formation, stress-tolerance response, and caries production. We have previously shown that CovR acts as a transcriptional repressor by binding to the upstream promoter regions of its target genes. Here, we report that in vivo, CovR activates the transcription of SMU.1882, which encodes a small peptide containing a double-glycine motif. We also show that SMU.1882 is transcriptionally linked to comA that encodes a putative ABC transporter protein. Several genes from man gene clusters that encode mannose phosphotranferase system flank SMU.1882 -comA genes. Genomic comparison with other streptococci indicates that SMU.1882 is uniquely present in S. mutans, while the man operon is conserved among all streptococci, suggesting that a genetic rearrangement might have taken place at this locus. With the use of a transcriptional reporter system and semi-quantitative RT-PCR, we demonstrated the transcriptional regulation of SMU.1882 by CovR. In vitro gel shift and DNase I foot-printing analyses with purified CovR suggest that CovR binds to a large region surrounding the -10 region of the P(1882). Using this information and comparing with other CovR regulated promoters, we have developed a putative consensus binding sequence for CovR. Although CovR binds to P(1882), in vitro experiments using purified S. mutans RpoD, E. coli RNA polymerase, and CovR did not activate transcription from this promoter. Thus, we speculate that in vivo, CovR may interfere with the binding of a repressor or requires a cofactor.

Role of purine biosynthesis in Bacillus anthracis pathogenesis and virulence

Bacillus anthracis, the etiological agent of anthrax, is a spore-forming, Gram-positive bacterium and a category A biothreat agent. Screening of a library of transposon-mutagenized B. anthracis spores identified a mutant displaying an altered phenotype that harbored a mutated gene encoding the purine biosynthetic enzyme PurH. PurH is a bifunctional protein that catalyzes the final steps in the biosynthesis of the purine IMP. We constructed and characterized defined purH mutants of the virulent B. anthracis Ames strain. The virulence of the purH mutants was assessed in guinea pigs, mice, and rabbits. The spores of the purH mutants were as virulent as wild-type spores in mouse intranasal and rabbit subcutaneous infection models but were partially attenuated in a mouse intraperitoneal model. In contrast, the purH mutant spores were highly attenuated in guinea pigs regardless of the administration route. The reduced virulence in guinea pigs was not due solely to a germination defect, since both bacilli and toxins were detected in vivo, suggesting that the significant attenuation was associated with a growth defect in vivo. We hypothesize that an intact purine biosynthetic pathway is required for the virulence of B. anthracis in guinea pigs.

Rational design of a plasmid origin that replicates efficiently in both gram-positive and gram-negative bacteria

BACKGROUND

Most plasmids replicate only within a particular genus or family.

METHODOLOGY/PRINCIPAL FINDINGS

Here we describe an engineered high copy number expression vector, pBAV1K-T5, that produces varying quantities of active reporter proteins in Escherichia coli, Acinetobacter baylyi ADP1, Agrobacterium tumefaciens, (all gram-negative), Streptococcus pneumoniae, Leifsonia shinshuensis, Peanibacillus sp. S18-36 and Bacillus subtilis (gram-positive).

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate the efficiency of pBAV1K-T5 replication in different bacterial species, thereby facilitating the study of proteins that don't fold well in E. coli and pathogens not amenable to existing genetic tools.

Staphylococcus aureus NrdH redoxin is a reductant of the class Ib ribonucleotide reductase

Staphylococci contain a class Ib NrdEF ribonucleotide reductase (RNR) that is responsible, under aerobic conditions, for the synthesis of deoxyribonucleotide precursors for DNA synthesis and repair. The genes encoding that RNR are contained in an operon consisting of three genes, nrdIEF, whereas many other class Ib RNR operons contain a fourth gene, nrdH, that determines a thiol redoxin protein, NrdH. We identified a 77-amino-acid open reading frame in Staphylococcus aureus that resembles NrdH proteins. However, S. aureus NrdH differs significantly from the canonical NrdH both in its redox-active site, C-P-P-C instead of C-M/V-Q-C, and in the absence of the C-terminal [WF]SGFRP[DE] structural motif. We show that S. aureus NrdH is a thiol redox protein. It is not essential for aerobic or anaerobic growth and appears to have a marginal role in protection against oxidative stress. In vitro, S. aureus NrdH was found to be an efficient reductant of disulfide bonds in low-molecular-weight substrates and proteins using dithiothreitol as the source of reducing power and an effective reductant for the homologous class Ib RNR employing thioredoxin reductase and NADPH as the source of the reducing power. Its ability to reduce NrdEF is comparable to that of thioredoxin-thioredoxin reductase. Hence, S. aureus contains two alternative thiol redox proteins, NrdH and thioredoxin, with both proteins being able to function in vitro with thioredoxin reductase as the immediate hydrogen donors for the class Ib RNR. It remains to be clarified under which in vivo physiological conditions the two systems are used.

Characterization of the haem-uptake system of the equine pathogen Streptococcus equi subsp. equi

Streptococcus equi possesses a haem-uptake system homologous to that of Streptococcus pyogenes and Streptococcus zooepidemicus. The system consists of two ligand-binding proteins (Shr and Shp) and proteins (HtsA–C) with homology to an ABC transporter. The haem-uptake system of S. equi differs from that of S. pyogenes and S. zooepidemicus in that Shr is truncated by two-thirds. This study focused on the SeShr, SeShp and SeHtsA proteins of S. equi. Analysis of shr, shp and shphtsA knockout mutants showed that all three proteins were expressed in vitro and that expression was upregulated under conditions of iron limitation. SeShr possesses no membrane-/cell wall-spanning sequences and was shown to be secreted. Both SeShp and SeHtsA were confirmed to be envelope-associated. Recombinant SeShp and SeHtsA proteins have been previously shown to bind haem and SeHtsA could capture haem from SeShp. This report extends these studies and shows that both SeShp and SeHtsA can sequester haem from haemoglobin but not from haemoglobin–haptoglobin complexes. Like full-length Shr, SeShr possesses haemoglobin and haemoglobin–haptoglobin binding ability but unlike full-length Shr, it lacks haem- or fibronectin-binding capabilities. Analysis of SeShr truncates showed that residues within and upstream of the near transporter (NEAT) domain are required for this ligand binding. Structural predictions suggest that truncation of NEAT1 in SeShr accounts for its impaired ability to bind haem. Haem and haemoglobin restored to almost normal the impaired growth rates of wild-type S. equi cultured under iron-limiting conditions. However, no difference in the growth rates of wild-type and mutants could be detected under the in vitro growth conditions tested.

Role of GlnR in acid-mediated repression of genes encoding proteins involved in glutamine and glutamate metabolism in Streptococcus mutans

The acid tolerance response (ATR) is one of the major virulence traits of Streptococcus mutans. In this study, the role of GlnR in acid-mediated gene repression that affects the adaptive ATR in S. mutans was investigated. Using a whole-genome microarray and in silico analyses, we demonstrated that GlnR and the GlnR box (ATGTNAN(7)TNACAT) were involved in the transcriptional repression of clusters of genes encoding proteins involved in glutamine and glutamate metabolism under acidic challenge. Reverse transcription-PCR (RT-PCR) analysis revealed that the coordinated regulation of the GlnR regulon occurred 5 min after acid treatment and that prolonged acid exposure (30 min) resulted in further reduction in expression. A lower level but consistent reduction in response to acidic pH was also observed in chemostat-grown cells, confirming the negative regulation of GlnR. The repression by GlnR through the GlnR box in response to acidic pH was further confirmed in the citBZC operon, containing genes encoding the first three enzymes in the glutamine/glutamate biosynthesis pathway. The survival rate of the GlnR-deficient mutant at pH 2.8 was more than 10-fold lower than that in the wild-type strain 45 min after acid treatment, suggesting that the GlnR regulon participates in S. mutans ATR. It is hypothesized that downregulation of the synthesis of the amino acid precursors in response to acid challenge would promote citrate metabolism to pyruvate, with the consumption of H(+) and potential ATP synthesis. Such regulation will ensure an optimal acid adaption in S. mutans.

Functional analysis of the quorum-sensing streptococcal invasion locus (sil)

Group A streptococcus (GAS) causes a wide variety of human diseases, and at the same time, GAS can also circulate without producing symptoms, similar to its close commensal relative, group G streptococcus (GGS). We previously identified, by transposon-tagged mutagenesis, the streptococcal invasion locus (sil). sil is a quorum-sensing regulated locus which is activated by the autoinducer peptide SilCR through the two-component system SilA-SilB. Here we characterize the DNA promoter region necessary for SilA-mediated activation. This site is composed of two direct repeats of 10 bp, separated by a spacer of 11 bp. Fusion of this site to gfp allowed us to systematically introduce single-base substitutions in the repeats region and to assess the relative contribution of various positions to promoter strength. We then developed an algorithm giving different weights to these positions, and performed a chromosome-wide bioinformatics search which was validated by transcriptome analysis. We identified 13 genes, mostly bacteriocin related, that are directly under the control of SilA. Having developed the ability to quantify SilCR signaling via GFP accumulation prompted us to search for GAS and GGS strains that sense and produce SilCR. While the majority of GAS strains lost sil, all GGS strains examined still possess the locus and ∼63% are able to respond to exogenously added SilCR. By triggering the autoinduction circle using a minute concentration of synthetic SilCR, we identified GAS and GGS strains that are capable of sensing and naturally producing SilCR, and showed that SilCR can be sensed across these streptococci species. These findings suggest that sil may be involved in colonization and establishment of commensal host-bacterial relationships.

Cell-to-cell communication in bacteria is termed quorum-sensing (QS), which is triggered by signaling molecules called autoinducers. In streptococci, autoinducers are synthesized as immature peptides that are processed, secreted, and then sensed by two-component systems (TCSs). As a result, the autoinducer's own expression is upregulated (autoinduction), subsequently creating an ultrasensitive switch that turns on more genes. Group A streptococcus (GAS) is a human pathogen that causes many infections, including necrotizing fasciitis (NF). Previously, we identified in a NF GAS strain a QS locus termed streptococcal invasion locus (sil). Due to a mutation in the autoinducer peptide-SilCR, it is not produced by this strain. Here we sought to better explore sil and to examine if SilCR can be produced by other GAS strains, or strains of its close relative group G streptococcus (GGS). To this end, we characterized the DNA promoter region responsible for the TCS-mediated activation upon sensing of SilCR, and based on bioinformatics and transcriptome analyses we identified genes that are directly affected by the autoinducer peptide. By converting SilCR response to fluorescence production and turning on the autoinduction circle with minute concentrations of synthetic SilCR, we discovered naturally SilCR-producing GAS and GGS strains, and showed that SilCR can be sensed across these species. Our study describes a novel way of cell-to-cell communications among streptococci.

Processing, assembly and localization of a Bacillus anthracis spore protein

All Bacillus spores are encased in macromolecular shells. One of these is a proteinacious shell called the coat that, in Bacillus subtilis, provides critical protective functions. The Bacillus anthracis spore is the infectious particle for the disease anthrax. Therefore, the coat is of particular interest because it may provide essential protective functions required for the appearance of anthrax. Here, we analyse a protein component of the spore outer layers that was previously designated BxpA. Our data indicate that a significant amount of BxpA is located below the spore coat and associated with the cortex. By SDS-PAGE, BxpA migrates as a 9 kDa species when extracted from Sterne strain spores, and as 11 and 14 kDa species from Ames strain spores, even though it has predicted masses of 27 and 29 kDa, respectively, in these two strains. We investigated the possibility that BxpA is subject to post-translational processing as previously suggested. In B. subtilis, a subset of coat proteins is proteolysed or cross-linked by the spore proteins YabG or Tgl, respectively. To investigate the possibility that similar processing occurs in B. anthracis, we generated mutations in the yabG or tgl genes in the Sterne and Ames strains and analysed the consequences for BxpA assembly by SDS-PAGE. We found that in a tgl mutant of B. anthracis, the apparent mass of BxpA increased. This is consistent with the possibility that Tgl directs the cross-linking of BxpA into a form that normally does not enter the gel. Unexpectedly, the apparent mass of BxpA also increased in a yabG mutant, suggesting a relatively complex role for proteolysis in spore protein maturation in B. anthracis. These data reveal a previously unobserved event in spore protein maturation in B. anthracis. We speculate that proteolysis and cross-linking are ubiquitous spore assembly mechanisms throughout the genus Bacillus.

Localization and assembly of proteins comprising the outer structures of the Bacillus anthracis spore

Bacterial spores possess a series of concentrically arranged protective structures that contribute to dormancy, survival and, ultimately, germination. One of these structures, the coat, is present in all spores. In Bacillus anthracis, however, the spore is surrounded by an additional, poorly understood, morphologically complex structure called the exosporium. Here, we characterize three previously discovered exosporium proteins called ExsFA (also known as BxpB), ExsFB (a highly related paralogue of exsFA/bxpB) and IunH (similar to an inosine-uridine-preferring nucleoside hydrolase). We show that in the absence of ExsFA/BxpB, the exosporium protein BclA accumulates asymmetrically to the forespore pole closest to the midpoint of the sporangium (i.e. the mother-cell-proximal pole of the forespore), instead of uniformly encircling the exosporium. ExsFA/BxpB may also have a role in coat assembly, as mutant spore surfaces lack ridges seen in wild-type spores and have a bumpy appearance. ExsFA/BxpB also has a modest but readily detected effect on germination. Nonetheless, an exsFA/bxpB mutant strain is fully virulent in both intramuscular and aerosol challenge models in Guinea pigs. We show that the pattern of localization of ExsFA/BxpB-GFP is a ring, consistent with a location for this protein in the basal layer of the exosporium. In contrast, ExsFB-GFP fluorescence is a solid oval, suggesting a distinct subcellular location for ExsFB-GFP. We also used these fusion proteins to monitor changes in the subcellular locations of these proteins during sporulation. Early in sporulation, both fusions were present throughout the mother cell cytoplasm. As sporulation progressed, GFP fluorescence moved from the mother cell cytoplasm to the forespore surface and formed either a ring of fluorescence, in the case of ExsFA/BxpB, or a solid oval of fluorescence, in the case of ExsFB. IunH-GFP also resulted in a solid oval of fluorescence. We suggest the interpretation that at least some ExsFB-GFP and IunH-GFP resides in the region between the coat and the exosporium, called the interspace.

3'-Phosphoadenosine-5'-phosphate phosphatase activity is required for superoxide stress tolerance in Streptococcus mutans

Aerobic microorganisms have evolved different strategies to withstand environmental oxidative stresses generated by various reactive oxygen species (ROS). For the facultative anaerobic human oral pathogen Streptococcus mutans, the mechanisms used to protect against ROS are not fully understood, since it does not possess catalase, an enzyme that degrades hydrogen peroxide. In order to elucidate the genes that are essential for superoxide stress response, methyl viologen (MV)-sensitive mutants of S. mutans were generated via ISS1 mutagenesis. Screening of approximately 2,500 mutants revealed six MV-sensitive mutants, each containing an insertion in one of five genes, including a highly conserved hypothetical gene, SMU.1297. Sequence analysis suggests that SMU.1297 encodes a hypothetical protein with a high degree of homology to the Bacillus subtilis YtqI protein, which possesses an oligoribonuclease activity that cleaves nano-RNAs and a phosphatase activity that degrades 3'-phosphoadenosine-5'-phosphate (pAp) and 3'-phosphoadenosine-5'-phosphosulfate (pApS) to produce AMP; the latter activity is similar to the activity of the Escherichia coli CysQ protein, which is required for sulfur assimilation. SMU.1297 was deleted using a markerless Cre-loxP-based strategy; the SMU.1297 deletion mutant was just as sensitive to MV as the ISS1 insertion mutant. Complementation of the deletion mutant with wild-type SMU.1297, in trans, restored the parental phenotype. Biochemical analyses with purified SMU.1297 protein demonstrated that it has pAp phosphatase activity similar to that of YtqI but apparently lacks an oligoribonuclease activity. The ability of SMU.1297 to dephosphorylate pApS in vivo was confirmed by complementation of an E. coli cysQ mutant with SMU.1297 in trans. Thus, our results suggest that SMU.1297 is involved in superoxide stress tolerance in S. mutans. Furthermore, the distribution of homologs of SMU.1297 in streptococci indicates that this protein is essential for superoxide stress tolerance in these organisms.

Functional genomics of Enterococcus faecalis: multiple novel genetic determinants for biofilm formation in the core genome

The ability of Enterococcus faecalis to form robust biofilms on host tissues and on abiotic surfaces such as catheters likely plays a major role in the pathogenesis of opportunistic antibiotic-resistant E. faecalis infections and in the transfer of antibiotic resistance genes. We have carried out a comprehensive analysis of genetic determinants of biofilm formation in the core genome of E. faecalis. Here we describe 68 genetic loci predicted to be involved in biofilm formation that were identified by recombinase in vivo expression technology (RIVET); most of these genes have not been studied previously. Differential expression of a number of these determinants during biofilm growth was confirmed by quantitative reverse transcription-PCR, and genetic complementation studies verified a role in biofilm formation for several candidate genes. Of particular interest was genetic locus EF1809, predicted to encode a regulatory protein of the GntR family. We isolated 14 independent nonsibling clones containing the putative promoter region for this gene in the RIVET screen; EF1809 also showed the largest increase in expression during biofilm growth of any of the genes tested. Since an in-frame deletion of EF1809 resulted in a severe biofilm defect that could be complemented by the cloned wild-type gene, we have designated EF1809 ebrA (enterococcal biofilm regulator). Most of the novel genetic loci identified in our studies are highly conserved in gram-positive bacterial pathogens and may thus constitute a pool of uncharacterized genes involved in biofilm formation that may be useful targets for drug discovery.

Use of 4-sulfophenyl isothiocyanate labeling and mass spectrometry to determine the site of action of the streptococcolytic peptidoglycan hydrolase zoocin A

Zoocin A is a streptococcolytic peptidoglycan hydrolase with an unknown site of action that is produced by Streptococcus equi subsp. zooepidemicus 4881. Zoocin A has now been determined to be a d-alanyl-l-alanine endopeptidase by digesting susceptible peptidoglycan with a combination of mutanolysin and zoocin A, separating the resulting muropeptides by reverse-phase high-pressure liquid chromatography, and analyzing them by mass spectrometry (MS) in both the positive- and negative-ion modes to determine their compositions. In order to distinguish among possible structures for these muropeptides, they were N-terminally labeled with 4-sulfophenyl isothiocyanate (SPITC) and analyzed by tandem MS in the negative-ion mode. This novel application of SPITC labeling and MS/MS analysis can be used to analyze the structure of peptidoglycans and to determine the sites of action of other peptidoglycan hydrolases.

Transcription of clpP is enhanced by a unique tandem repeat sequence in Streptococcus mutans

Streptococcus mutans, the primary causative agent of human dental caries, contains a single copy of the gene encoding ClpP, the chief intracellular protease responsible for tolerance to various environmental stresses. To better understand the role of ClpP in stress response, we investigated the regulation of clpP expression in S. mutans. Using semiquantitative reverse transcription-PCR analysis, we observed that, under nonstressed conditions, clpP expression is somewhat constant throughout the growth phases, although it gradually decreases as cells enter the late stationary phase. The half-life of the clpP transcript was found to be less than 1 minute. Sequence analysis of the clpP locus reveals the presence of a 50-bp tandem repeat sequence located immediately upstream of the clpP promoter (PclpP). PCR and DNA sequence analyses suggest that the number of tandem repeat units can vary from as few as two to as many as nine, depending on the particular S. mutans isolate. Further analysis, using a transcriptional reporter fusion consisting of PclpP fused to a promoterless gusA gene, indicates that the presence of the repeat sequence region within PclpP results in an approximately fivefold increase in expression from PclpP compared to the repeat-free transcriptional reporter fusion. CtsR, a transcriptional repressor that negatively regulates clpP expression, has no effect on this repeat-mediated induction of clpP transcription. Furthermore, the repeat sequence is not necessary for the induction of clpP under stress conditions. Database searches indicate that the region containing the tandem repeats is absent in the clpP loci in other bacteria, including other closely related Streptococcus spp., suggesting that the repeat sequences are specific for the induction of clpP expression in S. mutans. We speculate that a host-specific transcriptional activator might be involved in the upregulation of clpP expression in S. mutans.

Characterization of a Bacillus anthracis spore coat-surface protein that influences coat-surface morphology

Bacterial spores are encased in a multilayered proteinaceous shell, called the coat. In many Bacillus spp., the coat protects against environmental assault and facilitates germination. In Bacillus anthracis, the spore is the etiological agent of anthrax, and the functions of the coat likely contribute to virulence. Here, we characterize a B. anthracis spore protein, called Cotbeta, which is encoded only in the genomes of the Bacillus cereus group. We found that Cotbeta is synthesized specifically during sporulation and is assembled onto the spore coat surface. Our analysis of a cotbeta null mutant in the Sterne strain reveals that Cotbeta has a role in determining coat-surface morphology but does not detectably affect germination. In the fully virulent Ames strain, a cotbeta null mutation has no effect on virulence in a murine model of B. anthracis infection.

Construction of non-polar mutants in Haemophilus influenzae using FLP recombinase technology

Background

Nontypeable Haemophilus influenzae (NTHi) is a gram-negative bacterium that causes otitis media in children as well as other infections of the upper and lower respiratory tract in children and adults. We are employing genetic strategies to identify and characterize virulence determinants in NTHi. NTHi is naturally competent for transformation and thus construction of most mutants by common methodologies is relatively straightforward. However, new methodology was required in order to construct unmarked non-polar mutations in poorly expressed genes whose products are required for transformation. We have adapted the lambda red/FLP-recombinase-mediated strategy used in E. coli for use in NTHi.

Results

A cassette containing a spectinomycin resistance gene and an rpsL gene flanked by FRT sites was constructed. A PCR amplicon containing 50 base pairs of DNA homologous to the 5' and 3' ends of the gene to be disrupted and the cassette was generated, then recombineered into the target NTHi gene, cloned on a plasmid, using the lambda recombination proteins expressed in E. coli DY380. Thus, the gene of interest was replaced by the cassette. The construct was then transformed into a streptomycin resistant NTHi strain and mutants were selected on spectinomycin-containing growth media. A plasmid derived from pLS88 with a temperature sensitive replicon expressing the FLP recombinase gene under the control of the tet operator/repressor was constructed. This plasmid was electroporated into the NTHi mutant at the permissive temperature and FLP expression was induced using anhydrotetracycline. The recombinase recognizes the FRT sites and eliminates the antibiotic cassette by site-specific recombination, creating the unmarked non-polar mutation. The plasmid is cured by growth of cells at the restrictive temperature.

Conclusion

The products of the genes in the NTHi pilABCD operon are required for type IV pilus biogenesis and have a role in transformation. We demonstrated the utility of our methodology by the construction of a non-polar pilA mutation in NTHi strain 2019 and complementation of the mutation with a plasmid containing the pilA gene. Utilization of this approach allowed us to readily generate unmarked non-polar mutations in NTHi genes.

Shuttle expression plasmids for genetic studies in Streptococcus mutans

A set of shuttle plasmids containing four different constitutive promoters was generated to facilitate overexpression of foreign and native genes in streptococci, such as Streptococcus mutans. The four promoters that were chosen were: P(ami), P(spac), P(23) and P(veg). These promoters are active in many Gram-positive bacteria, and allow various levels of gene expression depending on the host bacterium. Shuttle plasmids were constructed based on two types of broad-host-range replication origins: a rolling-circle replicon (pSH71) and a theta replicon (pAMbeta1). Shuttle plasmids derived from the pAMbeta1 replicon were generated to avoid the structural and segregational stability problems associated with rolling-circle replication, since these problems may be encountered during large gene cloning. In a complementation assay, we used one such plasmid to express a gene in trans to show the utility of these plasmids. In addition, a series of plasmids was generated for the expression of recombinant proteins with an N-terminal 6xHis tag or a C-terminal Strep-tag fusion, and, using a gene derived from S. mutans, we showed a high level of recombinant protein expression in S. mutans and Streptococcus pyogenes. Since these plasmids contain broad-host-range replication origins, and because the selected promoters are functional in many bacteria, they can be used for gene expression studies, such as complementation and recombinant protein expression.

TrxR, a new CovR-repressed response regulator that activates the Mga virulence regulon in group A Streptococcus

Coordinate regulation of virulence factors by the group A streptococcus (GAS) Streptococcus pyogenes is important in this pathogen's ability to cause disease. To further elucidate the regulatory network in this human pathogen, the CovR-repressed two-component system (TCS) trxSR was chosen for further analysis based on its homology to a virulence-related TCS in Streptococcus pneumoniae. In a murine skin infection model, an insertion mutation in the response regulator gene, trxR, led to a significant reduction in lesion size, lesion severity, and lethality. Curing the trxR mutation restored virulence comparable to the wild-type strain. The trxSR operon was defined in vivo, and CovR was found to directly repress its promoter in vitro. DNA microarray analysis established that TrxR activates transcription of Mga-regulated virulence genes, which may explain the virulence attenuation of the trxR mutant. This regulation appears to occur by activation of the mga promoter, Pmga, as demonstrated by analysis of a luciferase reporter fusion. Complementation of the trxR mutant with trxR on a plasmid restored expression of Mga regulon genes and restored virulence in the mouse model to wild-type levels. TrxR is the first TCS shown to regulate Mga expression. Because it is CovR repressed, TrxR defines a new pathway by which CovR can influence Mga to affect pathogenesis in the GAS.

Streptococcus iniae M-like protein contributes to virulence in fish and is a target for live attenuated vaccine development

Background

Streptococcus iniae is a significant pathogen in finfish aquaculture, though knowledge of virulence determinants is lacking. Through pyrosequencing of the S. iniae genome we have identified two gene homologues to classical surface-anchored streptococcal virulence factors: M-like protein (simA) and C5a peptidase (scpI).

Methodology/Principal Findings

S. iniae possesses a Mga-like locus containing simA and a divergently transcribed putative mga-like regulatory gene, mgx. In contrast to the Mga locus of group A Streptococcus (GAS, S. pyogenes), scpI is located distally in the chromosome. Comparative sequence analysis of the Mgx locus revealed only one significant variant, a strain with an insertion frameshift mutation in simA and a deletion mutation in a region downstream of mgx, generating an ORF which may encode a second putative mga-like gene, mgx2. Allelic exchange mutagenesis of simA and scpI was employed to investigate the potential role of these genes in S. iniae virulence. Our hybrid striped bass (HSB) and zebrafish models of infection revealed that M-like protein contributes significantly to S. iniae pathogenesis whereas C5a peptidase-like protein does not. Further, in vitro cell-based analyses indicate that SiMA, like other M family proteins, contributes to cellular adherence and invasion and provides resistance to phagocytic killing. Attenuation in our virulence models was also observed in the S. iniae isolate possessing a natural simA mutation. Vaccination of HSB with the ΔsimA mutant provided 100% protection against subsequent challenge with a lethal dose of wild-type (WT) S. iniae after 1,400 degree days, and shows promise as a target for live attenuated vaccine development.

Conclusions/Significance

Analysis of M-like protein and C5a peptidase through allelic replacement revealed that M-like protein plays a significant role in S. iniae virulence, and the Mga-like locus, which may regulate expression of this gene, has an unusual arrangement. The M-like protein mutant created in this research holds promise as live-attenuated vaccine.

Environmental and growth phase regulation of the Streptococcus gordonii arginine deiminase genes

A 1,026-bp open reading frame sharing significant similarity with queA, which encodes a predicted S-adenosylmethionine:tRNA ribosyltransferase-isomerase responsible for queosine modification of tRNAs, was found immediately 5' of the gene for the transcriptional activator (ArcR) of the arginine deiminase system (ADS) operon of Streptococcus gordonii. The role of QueA in bacterial physiology is enigmatic, but loss of QueA has been shown to compromise stationary-phase survival or virulence in certain enteric bacteria. Interestingly, S. gordonii appears to be unique among ADS-positive bacteria in the linkage of queA with the ADS genes. A putative sigma(70) promoter (p(queA); TTGCCA-N(21)-TATAAT) was mapped 5' of queA by primer extension, and queA and arcR were shown to be cotranscribed. The expression from p(queA) was found to be constitutive under all conditions tested, but the expression of p(arcA), which drives the expression of the arc structural genes, was enhanced in stationary phase and could be induced by low pH and arginine. QueA and CcpA acted repressively on arc transcription, but neither QueA-deficient strains nor CcpA-deficient strains showed significant differences in arginine deiminase enzyme activities compared with the wild-type strain. The growth rate of a QueA-deficient strain did not differ significantly from that of the parental strain, but the QueA-deficient strain did not compete well with the wild-type during serial passage. In addition to the finding that ADS expression can be regulated separately by growth phase and pH, a significant linkage between the ADS, translational efficiency modulated by QueA, and post-exponential-phase survival of S. gordonii was found.

CcpA-mediated repression of streptolysin S expression and virulence in the group A streptococcus

CcpA is the global mediator of carbon catabolite repression (CCR) in gram-positive bacteria, and growing evidence from several pathogens, including the group A streptococcus (GAS), suggests that CcpA plays an important role in virulence gene regulation. In this study, a deletion of ccpA in an invasive M1 GAS strain was used to test the contribution of CcpA to pathogenesis in mice. Surprisingly, the DeltaccpA mutant exhibited a dramatic "hypervirulent" phenotype compared to the parental MGAS5005 strain, reflected as increased lethality in a model of systemic infection (intraperitoneal administration) and larger lesion size in a model of skin infection (subcutaneous administration). Expression of ccpA in trans from its native promoter was able to complement both phenotypes, suggesting that CcpA acts to repress virulence in GAS. To identify the CcpA-regulated gene(s) involved, a transcriptome analysis was performed on mid-logarithmic-phase cells grown in rich medium. CcpA was found to primarily repress 6% of the GAS genome (124 genes), including genes involved in sugar metabolism, transcriptional regulation, and virulence. Notably, the entire sag operon necessary for streptolysin S (SLS) production was under CcpA-mediated CCR, as was SLS hemolytic activity. Purified CcpA-His bound specifically to a cre within sagAp, demonstrating direct repression of the operon. Finally, SLS activity is required for the increased virulence of a DeltaccpA mutant during systemic infection but did not affect virulence in a wild-type background. Thus, CcpA acts to repress SLS activity and virulence during systemic infection in mice, revealing an important link between carbon metabolism and GAS pathogenesis.

Markerless multiple-gene-deletion system for Streptococcus mutans

Inactivation or selective modification is essential to elucidate the putative function of a gene. The present study describes an improved Cre-loxP-based method for markerless multiple gene deletion in Streptococcus mutans, the principal etiological agent of dental caries. This modified method uses two mutant loxP sites, which after recombination creates a double-mutant loxP site that is poorly recognized by Cre recombinase, facilitating multiple gene deletions in a single genetic background. The effectiveness of this modified strategy was demonstrated by the construction of both single and double gene deletions at the htrA and clpP loci on the chromosome of Streptococcus mutans. HtrA and ClpP play key roles in the processing and maturation of several important proteins, including many virulence factors. Deletion of these genes resulted in reducing the organism's ability to withstand exposure to low pH and oxidative agents. The method described here is simple and efficient and can be easily implemented for multiple gene deletions with S. mutans and other streptococci.

cadDX operon of Streptococcus salivarius 57.I

A CadDX system that confers resistance to Cd(2+) and Zn(2+) was identified in Streptococcus salivarius 57.I. Unlike with other CadDX systems, the expression of the cad promoter was negatively regulated by CadX, and the repression was inducible by Cd(2+) and Zn(2+), similar to what was found for CadCA systems. The lower G+C content of the S. salivarius cadDX genes suggests acquisition by horizontal gene transfer.

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

Carbon catabolite repression (CCR) allows bacteria to alter metabolism in response to the availability of specific sugar sources, and increasing evidence suggests that CCR is involved in regulating virulence gene expression in many pathogens. A scan of the M1 SF370 group A streptococcus (GAS) genome using a Bacillus subtilis consensus identified a number of potential catabolite-responsive elements (cre) important for binding by the catabolite control protein A (CcpA), a mediator of CCR in gram-positive bacteria. Intriguingly, a putative cre was identified in the promoter region of mga upstream of its distal P1 start of transcription. Electrophoretic mobility shift assays showed that a His-CcpA fusion protein was capable of binding specifically to the cre in Pmga in vitro. Deletion analysis of Pmga using single-copy Pmga-gusA reporter strains found that Pmga P1 and its upstream cre were not required for normal autoregulated mga expression from Pmga P2 as long as Mga was produced from its native locus. In fact, the Pmga P1 region appeared to show a negative influence on Pmga P2 in these studies. However, deletion of the cre at the native Pmga resulted in a reduction of total mga transcripts as determined by real-time reverse transcription-PCR, supporting a role for CcpA in initial expression. Furthermore, normal transcriptional initiation from the Pmga P1 start site alone was dependent on the presence of the cre. Importantly, inactivation of ccpA in the M6 GAS strain JRS4 resulted in a reduction in Pmga expression and Mga protein levels in late-logarithmic-phase cell growth. These data support a role for CcpA in the early activation of the mga promoter and establish a link between CCR and Mga regulation in the GAS.

The oligopeptide (opp) gene cluster of Streptococcus mutans: identification, prevalence, and characterization

INTRODUCTION

The Opp system is an ATP-binding cassette-type transporter formed by membrane-associated proteins required for the uptake of oligopeptides in bacteria. In gram-positive bacteria, the Opp system, and particularly the oligopeptide-binding protein (OppA), has been shown to be involved in different aspects of cell physiology, including intercellular communication and binding to host proteins.

METHODS

In the present study we began to investigate the Opp system of Streptococcus mutans, the main etiological agent of dental caries.

RESULTS

Five opp genes (oppABCDF) organized in a single operon were identified in the genome of the S. mutans UA159 strain. Amino acid sequence analyses showed that the S. mutans OppA is closely related to an ortholog found in Streptococcus agalactiae. Incubation of S. mutans UA159 cells with an anti-OppA-specific serum did not inhibit biofilm formation on polystyrene plates. Moreover, S. mutans UA159 derivatives carrying deletions on the oppA or oppB genes did not show significant growth impairment, increased sensitivity to aminopterin, or defective capacity to form biofilms on polystyrene wells in the presence or not of saliva. Remarkably, only two out of three laboratory strains and one out of seven clinical strains recovered from tooth decay processes harbored a copy of the oppA gene and expressed the OppA protein.

CONCLUSION

Collectively, these results indicate that, in contrast to other Streptococcus species, the S. mutans Opp system, and particularly the OppA protein, does not represent an important trait required for growth and colonization.

The BclB glycoprotein of Bacillus anthracis is involved in exosporium integrity

Anthrax is a highly fatal disease caused by the gram-positive, endospore-forming, rod-shaped bacterium Bacillus anthracis. Spores, rather than vegetative bacterial cells, are the source of anthrax infections. Spores of B. anthracis are enclosed by a prominent loose-fitting structure called the exosporium. The exosporium is composed of a basal layer and an external hair-like nap. Filaments of the hair-like nap are made up largely of a single collagen-like glycoprotein called BclA. A second glycoprotein, BclB, has been identified in the exosporium layer. The specific location of this glycoprotein within the exosporium layer and its role in the biology of the spore are unknown. We created a mutant strain of B. anthracis DeltaSterne that carries a deletion of the bclB gene. The mutant was found to possess structural defects in the exosporium layer of the spore (visualized by electron microscopy, immunofluorescence, and flow cytometry) resulting in an exosporium that is more fragile than that of a wild-type spore and is easily lost. Immunofluorescence studies also indicated that the mutant strain produced spores with increased levels of the BclA glycoprotein accessible to the antibodies on the surface. The resistance properties of the mutant spores were unchanged from those of the wild-type spores. A bclB mutation did not affect spore germination or kinetics of spore survival within macrophages. BclB plays a key role in the formation and maintenance of the exosporium structure in B. anthracis.

Bacillus anthracis spores of the bclA mutant exhibit increased adherence to epithelial cells, fibroblasts, and endothelial cells but not to macrophages

Bacillus anthracis is the causative agent of anthrax, and the spore form of the bacterium represents the infectious particle introduced into a host. The spore is surrounded by an exosporium, a loose-fitting membrane composed of proteins and carbohydrates from which hair-like projections extend. These projections are composed mainly of BclA (Bacillus-collagen-like protein of B. anthracis). To date, exact roles of the exosporium structure and BclA protein remain undetermined. We examined differences in spore binding of wild-type Ames and a bclA mutant of B. anthracis to bronchial epithelial cells as well as to the following other epithelial cells: A549, CHO, and Caco-2 cells; the IMR-90 fibroblast line; and human umbilical vein vascular endothelium cells. The binding of wild-type Ames spores to bronchial epithelial cells appeared to be a dose-dependent, receptor-ligand-mediated event. There were similar findings for the bclA mutant, with an additional nonspecific binding component likely leading to significantly more adherence to all nonprofessional phagocytic cell types. In contrast, we detected no difference in adherence and uptake of spores by macrophages for either the wild-type Ames or the bclA mutant strain. These results suggest that one potential role of the BclA fibers may be to inhibit nonspecific interactions between B. anthracis spores with nonprofessional phagocytic cells and thus direct the spores towards uptake by macrophages during initiation of infection in mammals.

A Bacillus anthracis-based in vitro system supports replication of plasmid pXO2 as well as rolling-circle-replicating plasmids

Capsule-encoding virulence plasmid pXO2 of Bacillus anthracis is predicted to replicate by a unidirectional theta-type mechanism. To gain a better understanding of the mechanism of replication of pXO2 and other plasmids in B. anthracis and related organisms, we have developed a cell-free system based on B. anthracis that can faithfully replicate plasmid DNA in vitro. The newly developed system was shown to support the in vitro replication of plasmid pT181, which replicates by the rolling-circle mechanism. We also demonstrate that this system supports the replication of plasmid pXO2 of B. anthracis. Replication of pXO2 required directional transcription through the plasmid origin of replication, and increased transcription through the origin resulted in an increase in plasmid replication.

Staphylococcus aureus ArcR controls expression of the arginine deiminase operon

We identified a single open reading frame that is strongly similar to ArcR, a member of the Crp/Fnr family of bacterial transcriptional regulators, in all sequenced Staphylococcus aureus genomes. The arcR gene encoding ArcR forms an operon with the arginine deiminase (ADI) pathway genes arcABDC that enable the utilization of arginine as a source of energy for growth under anaerobic conditions. In this report, we show that under anaerobic conditions, S. aureus growth is subject to glucose catabolic repression and is enhanced by arginine. Likewise, glucose and arginine have reciprocal effects on the transcription of the arcABDCR genes. Furthermore, we show using a mutant deleted for arcR that the transcription of the arc operon under anaerobic conditions depends strictly on a functional ArcR. These findings are supported by proteome analyses, which showed that under anaerobic conditions the expression of the ADI catabolic proteins depends on ArcR. Bioinformatic analysis of S. aureus ArcR predicts an N-terminal nucleotide binding domain and a C-terminal helix-turn-helix DNA binding motif. ArcR binds to a conserved Crp-like sequence motif, TGTGA-N(6)-TCACA, present in the arc promoter region and thereby activates the expression of the ADI pathway genes. Crp-like sequence motifs were also found in the regulatory regions of some 30 other S. aureus genes mostly encoding anaerobic enzymatic systems, virulence factors, and regulatory systems. ArcR was tested and found to bind to the regulatory regions of four such genes, adh1, lctE, srrAB, and lukM. In one case, for lctE, encoding l-lactate dehydrogenase, ArcR was able to bind only in the presence of cyclic AMP. These observations suggest that ArcR is likely to play an important role in the expression of numerous genes required for anaerobic growth.

Transcriptional regulation of the sil locus by the SilCR signalling peptide and its implications on group A streptococcus virulence

In the last two decades an increasing number of local outbreaks of invasive group A streptococcus (GAS) infections including necrotizing fasciitis (NF) have been reported. We identified the streptococcal invasion locus (sil) which is essential for virulence of the M14 strain JS95 isolated from an NF patient. This locus contains six genes: silA/B and silD/E encoding two-component system (TCS) and ABC transporter, respectively, homologous to the corresponding entities in the regulon of Streptococcus pneumoniae involved in genetic competence. Situated between these two units are silC and silCR, which highly overlap and are transcribed from the complementing strand at opposite directions. SilCR is a putative competence stimulating peptide, but in the M14 strain it has a start codon mutation. Deletion of silC or addition of synthetic SilCR attenuates virulence of the M14 strain. Here we found that silC and silCR form a novel regulatory circuit that controls the sil locus transcription. Under non-inducing conditions silC represses the silCR promoter. Externally added SilCR peptide activates the TCS, which in turn stimulates silCR transcription. Ongoing silCR transcription mediates the repression of the converging and overlapping silC transcript. Transcription of bacteriocin-like peptide (blp) operon mirrors the inverse relationships between the silC and silCR transcripts. It is upregulated by either addition of SilCR or deletion of silC. Moreover, expression of silC from a plasmid in a silC deleted-mutant significantly represses blp transcription. Finally, we show that 18% of clinically relevant GAS isolates possess sil and produce SilCR. Based on these results we propose a working model for regulation gene expression and virulence in GAS by the SilCR signalling peptide.

NrdR controls differential expression of the Escherichia coli ribonucleotide reductase genes

Escherichia coli possesses class Ia, class Ib, and class III ribonucleotide reductases (RNR). Under standard laboratory conditions, the aerobic class Ia nrdAB RNR genes are well expressed, whereas the aerobic class Ib nrdEF RNR genes are poorly expressed. The class III RNR is normally expressed under microaerophilic and anaerobic conditions. In this paper, we show that the E. coli YbaD protein differentially regulates the expression of the three sets of genes. YbaD is a homolog of the Streptomyces NrdR protein. It is not essential for growth and has been renamed NrdR. Previously, Streptomyces NrdR was shown to transcriptionally regulate RNR genes by binding to specific 16-bp sequence motifs, NrdR boxes, located in the regulatory regions of its RNR operons. All three E. coli RNR operons contain two such NrdR box motifs positioned in their regulatory regions. The NrdR boxes are located near to or overlap with the promoter elements. DNA binding experiments showed that NrdR binds to each of the upstream regulatory regions. We constructed deletions in nrdR (ybaD) and showed that they caused high-level induction of transcription of the class Ib RNR genes but had a much smaller effect on induction of transcription of the class Ia and class III RNR genes. We propose a model for differential regulation of the RNR genes based on binding of NrdR to the regulatory regions. The model assumes that differences in the positions of the NrdR binding sites, and in the sequences of the motifs themselves, determine the extent to which NrdR represses the transcription of each RNR operon.

A novel signal transduction system and feedback loop regulate fructan hydrolase gene expression in Streptococcus mutans

The fruA gene of Streptococcus mutans encodes for a secreted fructan hydrolase (fructanase), an established virulence determinant required for releasing D-fructose from levan- and inulin-type fructans. Expression of fruA is under the control of carbon catabolite repression and is induced by growth in fructans. In this report, we identified an operon in S. mutans UA159 encoding a two-component system flanked by two predicted carbohydrate-binding proteins that is absolutely required for the expression of fruA. All four genes were found to be required for optimal growth of S. mutans on inulin-containing medium and for transcriptional activation of fruA. Complementation assays using a plasmid expressing the response regulator suggested that the two-component system works in concert with the sugar-binding proteins. This operon was also shown to activate a four-gene cluster located immediately downstream and encoding an Enzyme II (EII(Lev)) for a fructose/mannose sugar : phosphotransferase enzyme, which was found to negatively regulate the expression of fruA. Using transcriptional fusions, it was found that fructose could signal induction of the fruA and levD operons through the two-component system/sugar-binding protein complex. A recombinant LevR protein was shown to bind to the promoter regions of fruA and levD in gel mobility shift assays. Thus, a 'four-component signal transduction system' activates fructan catabolism and the expression of an Enzyme II complex that functions in a feedback loop to sense the accumulation of the end-product of fructan degradation.

Physiologic effects of forced down-regulation of dnaK and groEL expression in Streptococcus mutans

Strains of Streptococcus mutans lacking DnaK or GroEL appear not to be isolable. To better distinguish the roles played by these chaperones/chaperonins in the physiology of S. mutans, we created a knockdown strategy to lower the levels of DnaK by over 95% in strain SM12 and the level of GroEL about 80% in strain SM13. Interestingly, GroEL levels were approximately twofold higher in SM12 than in the parent strain, but the levels of DnaK were not altered in the GroEL knockdown strain. Both SM12 and SM13 grew slower than the parent strain, had a strong tendency to aggregate in broth culture, and showed major changes in their proteomes. Compared with the wild-type strain, SM12 and SM13 had impaired biofilm-forming capacities when grown in the presence of glucose. The SM12 strain was impaired in its capacity to grow at 44 degrees C or at pH 5.0 and was more susceptible to H(2)O(2), whereas SM13 behaved like the wild-type strain under these conditions. Phenotypical reversions were noted for both mutants when cells were grown in continuous culture at a low pH, suggesting the occurrence of compensatory mutations. These results demonstrate that DnaK and GroEL differentially affect the expression of key virulence traits, including biofilm formation and acid tolerance, and support that these chaperones have evolved to accommodate unique roles in the context of this organism and its niche.

Genetic characterization and virulence role of the RALP3/LSA locus upstream of the streptolysin s operon in invasive M1T1 Group A Streptococcus

Group A Streptococcus (GAS) is a leading human pathogen associated with a wide spectrum of mucosal and invasive infections. GAS expresses a large number of virulence determinants whose expression is under the control of several transcriptional regulatory networks. Here we performed the first mutational analysis of a genetic locus immediately upstream of the streptolysin S biosynthetic operon in several GAS genome sequences, including that of the M1T1 serotype, the leading isolates associated with serious invasive disease. The locus consists of a predicted RofA-like stand-alone transcriptional regulator (RALP3) and the largest open reading frame in the GAS genome, encoding a predicted LPXSG motif cell wall-anchored protein we have named LSA (for "large surface-anchored" protein). Comparative reverse transcription-PCR analysis of wild-type M1T1 GAS and an isogenic RALP3-deficient mutant identifies RALP3 as a global transcriptional regulator affecting expression of numerous virulence factor genes, including those for strong repression of the hyaluronic acid capsule and cysteine protease production. RALP3 contributed to GAS epithelial cell invasion and bloodstream survival. LSA was found to be under negative regulation by RALP3 and to influence GAS-epithelial cell interactions and GAS antimicrobial peptide sensitivity. Isogenic M1T1 GAS mutants lacking either RALP3 or LSA were attenuated in a murine model of systemic infection, indicating that this locus plays a role in the virulence potential of the organism.

Morphogenesis of the Bacillus anthracis spore

Bacillus spp. and Clostridium spp. form a specialized cell type, called a spore, during a multistep differentiation process that is initiated in response to starvation. Spores are protected by a morphologically complex protein coat. The Bacillus anthracis coat is of particular interest because the spore is the infective particle of anthrax. We determined the roles of several B. anthracis orthologues of Bacillus subtilis coat protein genes in spore assembly and virulence. One of these, cotE, has a striking function in B. anthracis: it guides the assembly of the exosporium, an outer structure encasing B. anthracis but not B. subtilis spores. However, CotE has only a modest role in coat protein assembly, in contrast to the B. subtilis orthologue. cotE mutant spores are fully virulent in animal models, indicating that the exosporium is dispensable for infection, at least in the context of a cotE mutation. This has implications for both the pathophysiology of the disease and next-generation therapeutics. CotH, which directs the assembly of an important subset of coat proteins in B. subtilis, also directs coat protein deposition in B. anthracis. Additionally, however, in B. anthracis, CotH effects germination; in its absence, more spores germinate than in the wild type. We also found that SpoIVA has a critical role in directing the assembly of the coat and exosporium to an area around the forespore. This function is very similar to that of the B. subtilis orthologue, which directs the assembly of the coat to the forespore. These results show that while B. anthracis and B. subtilis rely on a core of conserved morphogenetic proteins to guide coat formation, these proteins may also be important for species-specific differences in coat morphology. We further hypothesize that variations in conserved morphogenetic coat proteins may play roles in taxonomic variation among species.

Fully virulent Bacillus anthracis does not require the immunodominant protein BclA for pathogenesis

The BclA protein is the immunodominant epitope on the surface of Bacillus anthracis spores; however, its roles in pathogenesis are unclear. We constructed a BclA deletion mutant (bclA) of the fully virulent Ames strain. This derivative retained full virulence in several small-animal models of infection despite the bclA deletion.

CooB is required for assembly but not transport of CS1 pilin

CS1 pili are filamentous proteinaceous appendages found on many enterotoxigenic Escherichia coli (ETEC) strains isolated from human diarrhoeal disease. They are thought to effect colonization of the upper intestine by facilitating binding to human ileal epithelial cells. We have identified a gene, cooB, which lies directly upstream of cooA, the gene that encodes the major structural CS1 protein. When translated in vitro, the protein product of cooB migrates in sodium dodecyl sulphate/polyacrylamide gel with an apparent molecular mass of 26 kDa, which is consistent with that predicted from its DNA sequence. We constructed a mutant allele (cooB-1) by insertion of the omega fragment, which inhibits transcription and translation, into the cooB gene in vitro. In a derivative of an ETEC strain with the cooB-1 mutation (JEF100) and a plasmid that encodes Rns (pEU2030), the positive regulator required for CS1 expression, no cooB and a greatly reduced level of cooA product was detectable in total cell extracts. The reduction of cooA in this strain appears to result from polarity of the cooB mutation because introduction of the wild-type cooA gene in trans causes production of CooA protein, which is found in cell pellet extracts, in extracts containing only surface proteins and in the culture supernatant. Therefore, in the absence of CooB, CooA is stable and it is transported through both inner and outer membranes. However, the cooB-1 strain with cooA in trans does not cause haemagglutination of bovine erythrocytes (the model system used to assay adherence mediated by coli surface antigen 1 (CS1) pili).(ABSTRACT TRUNCATED AT 250 WORDS)

A streptococcal protease that degrades CXC chemokines and impairs bacterial clearance from infected tissues

Group A Streptococcus (GAS) causes the life-threatening infection in humans known as necrotizing fasciitis (NF). Infected subcutaneous tissues from an NF patient and mice challenged with the same GAS strain possessed high bacterial loads but a striking paucity of infiltrating polymorphonuclear leukocytes (PMNs). Impaired PMN recruitment was attributed to degradation of the chemokine IL-8 by a GAS serine peptidase. Here, we use bioinformatics approach coupled with target mutagenesis to identify this peptidase as ScpC. We show that SilCR pheromone downregulates scpC transcription via the two-component system-SilA/B. In addition, we demonstrate that in vitro, ScpC degrades the CXC chemokines: IL-8 (human), KC, and MIP-2 (both murine). Furthermore, using a murine model of human NF, we demonstrate that ScpC, but not the C5a peptidase ScpA, is an essential virulence factor. An ScpC-deficient mutant is innocuous for untreated mice but lethal for PMN-depleted mice. ScpC degrades KC and MIP-2 locally in the infected skin tissues, inhibiting PMN recruitment. In conclusion, ScpC represents a novel GAS virulence factor functioning to directly inactivate a key element of the host innate immune response.

A novel FtsZ-like protein is involved in replication of the anthrax toxin-encoding pXO1 plasmid in Bacillus anthracis

Plasmid pXO1 encodes the tripartite anthrax toxin, which is the major virulence factor of Bacillus anthracis. In spite of the important role of pXO1 in anthrax pathogenesis, very little is known about its replication and maintenance in B. anthracis. We cloned a 5-kb region of the pXO1 plasmid into an Escherichia coli vector and showed that this plasmid can replicate when introduced into B. anthracis. Mutational analysis showed that open reading frame 45 (repX) of pXO1 was required for the replication of the miniplasmid in B. anthracis. Interestingly, repX showed limited homology to bacterial FtsZ proteins that are involved in cell division. A mutation in the predicted GTP binding domain of RepX abolished its replication activity. Genes almost identical to repX are contained on several megaplasmids in members of the Bacillus cereus group, including a B. cereus strain that causes an anthrax-like disease. Our results identify a novel group of FtsZ-related initiator proteins that are required for the replication of virulence plasmids in B. anthracis and possibly in related organisms. Such replication proteins may provide novel drug targets for the elimination of plasmids encoding the anthrax toxin and other virulence factors.

Domains required for transcriptional activation show conservation in the mga family of virulence gene regulators

Mga, or the multigene regulator of the group A streptococcus (GAS) (Streptococcus pyogenes), is a transcriptional regulator of virulence genes important for colonization and immune evasion. All serotypes of the GAS possess one of two divergent mga alleles (mga-1 or mga-2), and orthologues of Mga have also been identified in other pathogenic streptococci. To date, the only functional motifs established within Mga are two amino-terminal DNA-binding domains (HTH-3 and HTH-4). To uncover novel domains, a random mutagenesis screen using an M6 Mga (mga-1) was undertaken to find mutations leading to a defect in transcriptional activation of the Mga-regulated emm gene. In addition to mutations in the established DNA-binding domains, the screen also revealed mutations in a region conserved among several Mga orthologues. Alanine scanning helped resolve the boundaries of this conserved Mga domain (CMD-1) spanning from residues 10 to 15 of the protein, with the two flanking amino acid residues likely involved in protein stability. Transcriptional reporter analyses demonstrated the importance of CMD-1 for activation of Pemm and autoactivation of Pmga in the serotype M6 Mga. Mutational analyses showed that both CMD-1 and HTH-4 are also necessary for activation of the promoter target Pmrp in a divergent serotype M4 Mga (mga-2), suggesting a conserved functionality. However, in contrast to M6, the M4 Mga mutants did not show a defect in autoregulation. Mutation of similar conserved residues in the Mga-like regulator DmgB from S. dysgalactiae subsp. dysgalactiae showed that CMD-1 and HTH-4 are critical for transcriptional activation in this orthologue, implying that a common mechanism of virulence gene activation may exist for members of the Mga family of regulators.

The streptococcal Blr and Slr proteins define a family of surface proteins with leucine-rich repeats: camouflaging by other surface structures

Regions with tandemly arranged leucine-rich repeats (LRRs) have been found in many prokaryotic and eukaryotic proteins, in which they provide a remarkably versatile framework for the formation of ligand-binding sites. Bacterial LRR proteins include the recently described Slr protein of Streptococcus pyogenes, which is related to internalin A of Listeria monocytogenes. Here, we show that strains of the human pathogen Streptococcus agalactiae express a protein, designated Blr, which together with Slr defines a family of internalin A-related streptococcal LRR proteins. Analysis with specific antibodies demonstrated that Blr is largely inaccessible on S. agalactiae grown in vitro, but surface exposure was increased approximately 100-fold on mutants lacking polysaccharide capsule. In S. pyogenes, surface exposure of Slr was not affected in a mutant lacking hyaluronic acid capsule but was increased >20-fold in mutants lacking M protein or protein F. Thus, both Blr and Slr are efficiently camouflaged by other surface structures on bacteria grown in vitro. When Blr and Slr exposed on the bacterial surface were compared, they exhibited only little immunological cross-reactivity, in spite of extensive residue identity, suggesting that their surface-exposed parts have been under evolutionary pressure to diverge functionally and/or antigenically. These data identify a family of immunologically diverse streptococcal LRR proteins that show unexpected complexity in their interactions with other bacterial surface components.

Regulation and physiologic significance of the agmatine deiminase system of Streptococcus mutans UA159

We previously demonstrated that Streptococcus mutans expresses a functional agmatine deiminase system (AgDS) encoded by the agmatine-inducible aguBDAC operon (A. R. Griswold, Y. Y. Chen, and R. A. Burne, J. Bacteriol. 186:1902-1904, 2004). The AgDS yields ammonia, CO2, and ATP while converting agmatine to putrescine and is proposed to augment the acid resistance properties and pathogenic potential of S. mutans. To initiate a study of agu gene regulation, the aguB transcription initiation site was identified by primer extension and a putative sigma70-like promoter was mapped 5' to aguB. Analysis of the genome database revealed an open reading frame (SMU.261c) encoding a putative transcriptional regulator located 239 bases upstream of aguB. Inactivation of SMU.261c decreased AgD activity by sevenfold and eliminated agmatine induction. AgD was also found to be induced by certain environmental stresses, including low pH and heat, implying that the AgDS may also be a part of a general stress response pathway of this organism. Interestingly, an AgDS-deficient strain was unable to grow in the presence of 20 mM agmatine, suggesting that the AgDS converts a growth-inhibitory substance into products that can enhance acid tolerance and contribute to the competitive fitness of the organism at low pH. The capacity to detoxify and catabolize agmatine is likely to have major ramifications on oral biofilm ecology.

Plasmid-specified FemABX-like immunity factor in Staphylococcus sciuri DD 4747

A plasmid from Staphylococcus sciuri DD 4747 had three open reading frames: a replication gene, an N-acetylmuramyl-l-alanine amidase-like gene, and a gene similar to the lysostaphin endopeptidase resistance gene (epr/lif). The epr-like gene was introduced into S. aureus RN4220; the recombinant strain was more resistant to lysostaphin endopeptidase and its cell wall peptidoglycan contained more serines and fewer glycines than the parental strain with the shuttle vector alone. Based on both its function and its similarity to femAB, this gene is a member of the femABX-like immunity gene family. Furthermore, this is the first example of a femABX-like immunity gene that is not linked to the gene for the bacteriolytic enzyme against which it specifies immunity.

Characterization of MtsR, a new metal regulator in group A streptococcus, involved in iron acquisition and virulence

Group A streptococcus (GAS) is a common pathogen of the human skin and mucosal surfaces capable of producing a variety of diseases. In this study, we investigated regulation of iron uptake in GAS and the role of a putative transcriptional regulator named MtsR (for Mts repressor) with homology to the DtxR family of metal-dependent regulatory proteins. An mtsR mutant was constructed in NZ131 (M49 serotype) and analyzed. Western blot and RNA analysis showed that mtsR inactivation results in constitutive transcription of the sia (streptococcal iron acquisition) operon, which was negatively regulated by iron in the parent strain. A recombinant MtsR with C-terminal His(6) tag fusion (rMtsR) was cloned and purified. Electrophoretic mobility gel shift assays demonstrated that rMtsR specifically binds to the sia promoter region in an iron- and manganese-dependent manner. Together, these observations indicate that MtsR directly represses the sia operon during cell growth under conditions of high metal levels. Consistent with deregulation of iron uptake, the mtsR mutant is hypersensitive to streptonigrin and hydrogen peroxide, and (55)Fe uptake assays demonstrate that it accumulates 80% +/- 22.5% more iron than the wild-type strain during growth in complete medium. Studies with a zebrafish infection model revealed that the mtsR mutant is attenuated for virulence in both the intramuscular and the intraperitoneal routes. In conclusion, MtsR, a new regulatory protein in GAS, controls iron homeostasis and has a role in disease production.

Role of HtrA in surface protein expression and biofilm formation by Streptococcus mutans

The HtrA surface protease in gram-positive bacteria is involved in the processing and maturation of extracellular proteins and degradation of abnormal or misfolded proteins. Inactivation of htrA has been shown to affect the tolerance to thermal and environmental stress and to reduce virulence. We found that inactivation of Streptococcus mutans htrA by gene-replacement also resulted in a reduced ability to withstand exposure to low and high temperatures, low pH, and oxidative and DNA damaging agents. The htrA mutation affected surface expression of several extracellular proteins including glucan-binding protein B (GbpB), glucosyltransferases, and fructosyltransferase. In addition, htrA mutation also altered the surface expression of enolase and glyceraldehyde-3-phosphate dehydrogenease, two glycolytic enzymes that are known to be present on the streptococcal cell surface. As expected, microscopic analysis of in vitro grown biofilm structure revealed that the htrA deficient biofilms adopted a much more granular patchy appearance, rather than the relatively smooth confluent layer normally seen in the wild type. These results suggest that HtrA plays an important role in the biogenesis of extracellular proteins including surface associated glycolytic enzymes and in biofilm formation of S. mutans.

Transcriptional analysis of the Bacillus anthracis capsule regulators

The poly-d-glutamic acid capsule of Bacillus anthracis is essential for virulence. Control of capsule synthesis occurs at the level of transcription and involves positive regulation of the capsule biosynthetic operon capBCAD by a CO2/bicarbonate signal and three plasmid-borne regulators: atxA, acpA, and acpB. Although the molecular mechanism for control of cap transcription is unknown, atxA affects cap expression via positive control of acpA and acpB, two genes with partial functional similarity. Transcriptional analyses of a genetically complete strain indicate that capB expression is several hundred-fold higher during growth in 5% CO2 compared to growth in air. atxA was expressed appreciably during growth in air and induced only 2.5-fold by CO2. In contrast, expression of acpA and acpB was induced up to 23-fold and 59-fold, respectively, by CO2. The 5'-end mapping of gene transcripts revealed atxA-regulated and atxA-independent apparent transcription start sites for capB, acpA, and acpB. Transcripts mapping to all atxA-regulated start sites were increased during growth in elevated CO2. The acpA gene has one atxA-regulated and one atxA-independent start site. acpB lies downstream of capBCAD. A single atxA-independent start site maps immediately upstream of acpB. atxA-mediated control of acpB appears to occur via transcriptional read-through from atxA-dependent start sites 5' of capB. One atxA-independent and two atxA-regulated start sites map upstream of capB. Transcription from the atxA-regulated start sites of capBCAD was reduced significantly in an acpA acpB double mutant but unaffected in mutants with deletion of only acpA or acpB, in agreement with the current model for epistatic relationships between the regulators.