A 60-kilodalton immunodominant glycoprotein is essential for cell wall integrity and the maintenance of cell shape in Streptococcus mutans

Another Breaker of the Wall: the Biological Function of the Usp45 Protein of Lactococcus lactis

Lactococcus lactis is a Gram-positive bacterium that is widely used as a cell factory for the expression of heterologous proteins that are relevant in the pharmaceutical and nutraceutical fields. The signal peptide of the major secreted protein of L. lactis, Usp45, has been employed extensively in engineering strategies to secrete proteins of interest. However, the biological function of Usp45 has remained obscure despite more than 25 years of research. Studies on Usp45 homologs in other Gram-positive bacteria suggest that Usp45 may play a role in cell wall turnover processes. Here, we show the effect of inactivation and overexpression of the usp45 gene on L. lactis growth, phenotype, and cell division. Our results are in agreement with those obtained in streptococci and demonstrate that the L. lactis Usp45 protein is essential for proper cell division. We also show that the usp45 promoter is highly activated by galactose. Overall, our results indicate that Usp45 mediates cell separation, probably by acting as a peptidoglycan hydrolase.IMPORTANCE The cell wall, composed mainly of peptidoglycan, is key to maintaining the cell shape and protecting the cell from bursting. Peptidoglycan degradation by peptidoglycan hydrolysis and autolysins occurs during growth and cell division. Since peptidoglycan hydrolases are important for virulence, envelope integrity, and regulation of cell division, it is valuable to investigate their function and regulation. Notably, PcsB-like proteins such as Usp45 have been proposed as new targets for antimicrobial drugs and could also be target for the development of food-grade suicide systems. In addition, although various other expression and secretion systems have been developed for use in Lactococcus lactis, the most-used signal peptide for protein secretion in this bacterium is that of the Usp45 protein. Thus, elucidating the biological function of Usp45 and determining the factors affecting its expression would contribute to optimize several applications.

Essentiality and function of WalK/WalR two-component system: the past, present, and future of research

The WalK/WalR two-component system (TCS), originally identified in Bacillus subtilis, is very highly conserved in gram-positive bacteria, including several important pathogens. The WalK/WalR TCS appears to be involved in the growth of most bacterial species encoding it. Previous studies have indicated conserved functions of this system, defining this signal transduction pathway as a crucial regulatory system for cell wall metabolism. Because of such effects on essential functions, this system is considered a potential target for anti-infective therapeutics. In this review, we discuss the role of WalK/WalR TCS in different bacterial cells, focusing on the function of the genes in its regulon as well as the variations in walRK operon structure, its auxiliary proteins, and the composition of its regulon. We also discuss recent experimental data addressing its essential function and the potential type of signal being sensed by B. subtilis. This review also focuses on the potential future research.

Extracellular SalB Contributes to Intrinsic Cephalosporin Resistance and Cell Envelope Integrity in Enterococcus faecalis

Enterococci are major causes of hospital-acquired infections. Intrinsic resistance to cephalosporins is a universal trait among clinically relevant enterococci. Cephalosporin resistance enables enterococci to proliferate to high densities in the intestines of patients undergoing cephalosporin treatment, a precursor to the emergence of infection. However, the genetic and biochemical mechanisms of intrinsic cephalosporin resistance in enterococci are not well understood. A two-component signal transduction system, CroR/S, is required for cephalosporin resistance in enterococci. Although the CroR/S regulon is not well defined, one gene reported to be CroR dependent in Enterococcus faecalis JH2-2 encodes an extracellular putative peptidoglycan hydrolase, SalB. To test the hypothesis that SalB is responsible for CroR-dependent cephalosporin resistance, we examined ΔsalB mutants in multiple genetic lineages of E. faecalis, revealing that SalB is required not only for intrinsic cephalosporin resistance but also for maintenance of cell envelope integrity in the absence of antibiotic stress. The N-terminal signal sequence is necessary for SalB secretion, and secretion is required for SalB to promote cephalosporin resistance. Functional dissection revealed that the C-terminal SCP domain of SalB is essential for biological activity and identified three residues within the SCP domain that are required for the stability and function of SalB. Additionally, we found that in contrast to what is seen in E. faecalis JH2-2, SalB is not regulated by the CroR/S two-component system in E. faecalis OG1, suggesting diversity in the CroR/S regulon among distinct lineages of E. faecalis IMPORTANCE Resistance to cephalosporins is universal among clinically relevant enterococci, enabling enterococcal proliferation to high densities in the intestines of patients undergoing cephalosporin treatment, a precursor to the emergence of infection. Disabling cephalosporin resistance could therefore reduce the incidence of enterococcal infections. However, the genetic and biochemical mechanisms of cephalosporin resistance are not well understood. The significance of this work is the identification of a novel extracellular factor (SalB) that promotes cephalosporin resistance in E. faecalis, which could potentially serve as a target for therapeutics that impair enterococcal cephalosporin resistance. Additionally, our work highlights the importance of the C-terminal SCP domain of SalB, including several conserved residues within the SCP domain, for the ability of SalB to promote cephalosporin resistance.

Collagen-binding proteins of Streptococcus mutans and related streptococci

The ability of Streptococcus mutans to interact with collagen through the expression of collagen-binding proteins (CBPs) bestows this oral pathogen with an alternative to the sucrose-dependent mechanism of colonization classically attributed to caries development. Based on the abundance and distribution of collagen throughout the human body, stringent adherence to this molecule grants S. mutans with the opportunity to establish infection at different host sites. Surface proteins, such as SpaP, WapA, Cnm and Cbm, have been shown to bind collagen in vitro, and it has been suggested that these molecules play a role in colonization of oral and extra-oral tissues. However, robust collagen binding is not achieved by all strains of S. mutans, particularly those that lack Cnm or Cbm. These observations merit careful dissection of the contribution from these different CBPs towards tissue colonization and virulence. In this review, we will discuss the current understanding of mechanisms used by S. mutans and related streptococci to colonize collagenous tissues, and the possible contribution of CBPs to infections in different sites of the host.

Evidence for the Sialylation of PilA, the PI-2a Pilus-Associated Adhesin of Streptococcus agalactiae Strain NEM316

Streptococcus agalactiae (or Group B Streptococcus, GBS) is a commensal bacterium present in the intestinal and urinary tracts of approximately 30% of humans. We and others previously showed that the PI-2a pilus polymers, made of the backbone pilin PilB, the tip adhesin PilA and the cell wall anchor protein PilC, promote adhesion to host epithelia and biofilm formation. Affinity-purified PI-2a pili from GBS strain NEM316 were recognized by N-acetylneuraminic acid (NeuNAc, also known as sialic acid) specific lectins such as Elderberry Bark Lectin (EBL) suggesting that pili are sialylated. Glycan profiling with twenty different lectins combined with monosaccharide composition by HPLC suggested that affinity-purified PI-2a pili are modified by N-glycosylation and decorated with sialic acid attached to terminal galactose. Analysis of various relevant mutants in the PI-2a pilus operon by flow-cytometry and electron microscopy analyses pointed to PilA as the pilus subunit modified by glycosylation. Double labeling using PilB antibody and EBL lectin, which specifically recognizes N-acetylneuraminic acid attached to galactose in α-2, 6, revealed a characteristic binding of EBL at the tip of the pilus structures, highly reminiscent of PilA localization. Expression of a secreted form of PilA using an inducible promoter showed that this recombinant PilA binds specifically to EBL lectin when produced in the native GBS context. In silico search for potentially glycosylated asparagine residues in PilA sequence pointed to N427 and N597, which appear conserved and exposed in the close homolog RrgA from S. pneumoniae, as likely candidates. Conversion of these two asparagyl residues to glutamyl resulted in a higher instability of PilA. Our results provide the first evidence that the tip PilA adhesin can be glycosylated, and suggest that this modification is critical for PilA stability and may potentially influence interactions with the host.

The sweet tooth of bacteria: common themes in bacterial glycoconjugates

Humans have been increasingly recognized as being superorganisms, living in close contact with a microbiota on all their mucosal surfaces. However, most studies on the human microbiota have focused on gaining comprehensive insights into the composition of the microbiota under different health conditions (e.g., enterotypes), while there is also a need for detailed knowledge of the different molecules that mediate interactions with the host. Glycoconjugates are an interesting class of molecules for detailed studies, as they form a strain-specific barcode on the surface of bacteria, mediating specific interactions with the host. Strikingly, most glycoconjugates are synthesized by similar biosynthesis mechanisms. Bacteria can produce their major glycoconjugates by using a sequential or an en bloc mechanism, with both mechanistic options coexisting in many species for different macromolecules. In this review, these common themes are conceptualized and illustrated for all major classes of known bacterial glycoconjugates, with a special focus on the rather recently emergent field of glycosylated proteins. We describe the biosynthesis and importance of glycoconjugates in both pathogenic and beneficial bacteria and in both Gram-positive and -negative organisms. The focus lies on microorganisms important for human physiology. In addition, the potential for a better knowledge of bacterial glycoconjugates in the emerging field of glycoengineering and other perspectives is discussed.

Activated human nasal epithelial cells modulate specific antibody response against bacterial or viral antigens

Nasal mucosa is an immune responsive organ evidenced by eliciting both specific local secretory IgA and systemic IgG antibody responses with intra-nasal administration of antigens. Nevertheless, the role of nasal epithelial cells in modulating such responses is unclear. Human nasal epithelial cells (hNECs) obtained from sinus mucosa of patients with chronic rhinosinusitis were cultured in vitro and firstly were stimulated by Lactococcus lactis bacterium-like particles (BLPs) in order to examine their role on antibody production. Secondly, both antigens of immunodominant protein IDG60 from oral Streptococcus mutans and hemagglutinin (HA) from influenza virus were tested to evaluate the specific antibody response. Stimulated hNECs by BLPs exhibited a significant increase in the production of interleukin-6 (IL-6), and thymic stromal lymphopoietin (TSLP). Conditioned medium of stimulated hNECs has effects on enhancing the proliferation of CD4+ T cells together with interferon-γ and IL-5 production, increasing the costimulatory molecules on dendritic cells and augmenting the production of IDG60 specific IgA, HA specific IgG, IgA by human peripheral blood lymphocytes. Such production of antigen specific IgG and IgA is significantly counteracted in the presence of IL-6 and TSLP neutralizing antibodies. In conclusion, properly stimulated hNECs may impart immuno-modulatory effects on the antigen-specific antibody response at least through the production of IL-6 and TSLP.

Use of a mariner-based transposon mutagenesis system to isolate Clostridium perfringens mutants deficient in gliding motility

Clostridium perfringens is an anaerobic Gram-positive pathogen that causes many human and animal diseases, including food poisoning and gas gangrene. C. perfringens lacks flagella but possesses type IV pili (TFP). We have previously shown that C. perfringens can glide across an agar surface in long filaments composed of individual bacteria attached end to end and that two TFP-associated proteins, PilT and PilC, are needed for this. To discover additional gene products that play a role in gliding, we developed a plasmid-based mariner transposon mutagenesis system that works effectively in C. perfringens. More than 10,000 clones were screened for mutants that lacked the ability to move away from the edge of a colony. Twenty-four mutants (0.24%) were identified that fit the criteria. The genes containing insertions that affected gliding motility fell into nine different categories. One gene, CPE0278, which encodes a homolog of the SagA cell wall-dependent endopeptidase, acquired distinct transposon insertions in two independent mutants. sagA mutants were unable to form filaments due to a complete lack of end-to-end connections essential for gliding motility. Complementation of the sagA mutants with a wild-type copy of the gene restored gliding motility. We constructed an in-frame deletion mutation in the sagA gene and found that this mutant had a phenotype similar to those of the transposon mutants. We hypothesize that the sagA mutant strains are unable to form the molecular complexes which are needed to keep the cells in an end-to-end orientation, leading to separation of daughter cells and the inability to carry out gliding motility.

Role of the Group B antigen of Streptococcus agalactiae: a peptidoglycan-anchored polysaccharide involved in cell wall biogenesis

Streptococcus agalactiae (Group B streptococcus, GBS) is a leading cause of infections in neonates and an emerging pathogen in adults. The Lancefield Group B carbohydrate (GBC) is a peptidoglycan-anchored antigen that defines this species as a Group B Streptococcus. Despite earlier immunological and biochemical characterizations, the function of this abundant glycopolymer has never been addressed experimentally. Here, we inactivated the gene gbcO encoding a putative UDP-N-acetylglucosamine-1-phosphate:lipid phosphate transferase thought to catalyze the first step of GBC synthesis. Indeed, the gbcO mutant was unable to synthesize the GBC polymer, and displayed an important growth defect in vitro. Electron microscopy study of the GBC-depleted strain of S. agalactiae revealed a series of growth-related abnormalities: random placement of septa, defective cell division and separation processes, and aberrant cell morphology. Furthermore, vancomycin labeling and peptidoglycan structure analysis demonstrated that, in the absence of GBC, cells failed to initiate normal PG synthesis and cannot complete polymerization of the murein sacculus. Finally, the subcellular localization of the PG hydrolase PcsB, which has a critical role in cell division of streptococci, was altered in the gbcO mutant. Collectively, these findings show that GBC is an essential component of the cell wall of S. agalactiae whose function is reminiscent of that of conventional wall teichoic acids found in Staphylococcus aureus or Bacillus subtilis. Furthermore, our findings raise the possibility that GBC-like molecules play a major role in the growth of most if not all beta-hemolytic streptococci.

Group A streptococcus adheres to pharyngeal epithelial cells with salivary proline-rich proteins via GrpE chaperone protein

Group A Streptococcus pyogenes (GAS) is an important human pathogen that frequently causes pharyngitis. GAS organisms can adhere to and invade pharyngeal epithelial cells, which are overlaid by salivary components. However, the role of salivary components in GAS adhesion to pharyngeal cells has not been reported precisely. We collected human saliva and purified various salivary components, including proline-rich protein (PRP), statherin, and amylase, and performed invasion assays. The GAS-HEp-2 association ratio (invasion/adhesion ratio) and invasion ratio of GAS were increased significantly with whole human saliva and PRP, while the anti-PRP antibody inhibited the latter. GAS strain NY-5, which lacks M and F proteins on the cell surface, was promoted to cohere with HEp-2 cells by whole human saliva and PRP. The 28-kDa protein of GAS bound to PRP and was identified as GrpE, a chaperone protein, whereas the N-terminal of GrpE was found to bind to PRP. A GrpE-deficient mutant of GAS strain B514Sm, TR-45, exhibited a reduced ability to adhere to and invade HEp-2 cells. Microscopic observations showed the GrpE was mainly expressed on the surface of the cell division site of GAS. Furthermore, GrpE-deficient mutants of GAS and Streptococcus pneumoniae showed an elongated morphology as compared with the wild type. Taken together, this is the first study to show an interaction between salivary PRP and GAS GrpE, which plays an important role in GAS infection on the pharynx, whereas the expression of GrpE on the surface of GAS helps to maintain morphology.

Antimicrobial and osteogenic effect of Ag-implanted titanium with a nanostructured surface

Ag-implanted titanium with a nanostructured surface was prepared by hydrothermal treatment with H(2)O(2) followed by Ag plasma immersion ion implantation. Streptococcus mutans, Porphyromonas gingivalis and Candida albicans were chosen for antimicrobial tests. Genes related to microbial structure or adhesion, namely glucan-binding proteins B (GbpB), fimbria protein A (FimA), and agglutinin-like sequence4 (Als4), were examined. The osteoblast's attachment, viability, and quantitative analysis of osteogenic gene expression (Alp, Ocn, RunX2) on titanium surfaces were evaluated. Scanning electron microscopy (SEM) revealed that Ag nanoparticles of approximately 10 nm were incorporated on the nanostructured surface of titanium after Ag plasma immersion ion implantation. Trials showed that 93.99% of S. mutans, 93.57% of P. g, and 89.78% of C. albicans were killed on the Ag-implanted titanium with a nanostructured surface. Gene expressions from the three microorganisms confirmed the antimicrobial activities of the Ag-implanted titanium with a nanostructured surface. Furthermore, the adhesive images and viability assays indicated that the Ag-implanted titanium with a nanostructured surface did not impair osteoblasts. The expressions of osteoblast phenotype genes in cells grown on the Ag-implanted titanium surface were significantly increased. The results of this study suggest that the Ag-implanted titanium with a nanostructured surface displays good antimicrobial properties, reducing gene expressions of microorganisms, and excellent cell adhesion and osteogenic effects.

Identification of SagA as a novel vaccine target for the prevention of Enterococcus faecium infections

Infections caused by multiresistant Gram-positive bacteria represent a major health burden in the community as well as in hospitalized patients. Enterococci, especially Enterococcus faecium, are well-known pathogens of hospitalized patients and are frequently linked with resistance against multiple antibiotics, which compromises effective therapy. Rabbit immune serum raised against heat-killed E. faecium E155, a HiRECC clone, was used in an opsonophagocytic assay, an inhibition assay and a mouse bacteraemia model to identify targets of opsonic and protective antibodies. Serum against whole heat-killed bacteria was opsonic and recognized a protein of about 72 kDa that was abundantly secreted. This protein, identified as SagA by LC-ES-MS/MS, was expressed in Escherichia coli and purified. Rabbit serum raised against the purified protein showed opsonic killing activity that was inhibited by almost 100 % using 100 µg purified protein ml−1. In a mouse bacteraemia model, a statistically significant reduction of the colony counts in blood was shown with immune rabbit serum compared with preimmune serum using the homologous and a heterologous vancomycin-resistant enterococci (VRE) strain. These results indicate that SagA could be used as a promising vaccine target to treat and/or prevent VRE bacteraemia.

Effect of lectins from Diocleinae subtribe against oral Streptococci

Surface colonization is an essential step in biofilm development. The ability of oral pathogens to adhere to tooth surfaces is directly linked with the presence of specific molecules at the bacterial surface that can interact with enamel acquired pellicle ligands. In light of this, the aim of this study was to verify inhibitory and antibiofilm action of lectins from the Diocleinaesubtribe against Streptococcus mutans and Streptococcus oralis. The inhibitory action against planctonic cells was assessed using lectins from Canavaliaensi formis (ConA), Canavalia brasiliensis (ConBr), Canavalia maritima (ConM), Canavalia gladiata (CGL) and Canavalia boliviana (ConBol). ConBol, ConBr and ConM showed inhibitory activity on S. mutans growth. All lectins, except ConA, stimulated significantly the growth of S. oralis. To evaluate the effect on biofilm formation, clarified saliva was added to 96-well, flat-bottomed polystyrene plates, followed by the addition of solutions containing 100 or 200 µg/mL of the selected lectins. ConBol, ConM and ConA inhibited the S. mutans biofilms. No effects were found on S. oralis biofilms. Structure/function analysis were carried out using bioinformatics tools. The aperture and deepness of the CRD (Carbohydrate Recognition Domain) permit us to distinguish the two groups of Canavalia lectins in accordance to their actions against S. mutans and S. oralis. The results found provide a basis for encouraging the use of plant lectins as biotechnological tools in ecological control and prevention of caries disease.

Absence of pneumococcal PcsB is associated with overexpression of LysM domain-containing proteins

The streptococcal protein required for cell separation B (PcsB) is predicted to play an important role in peptidoglycan metabolism, based on sequence motifs and altered phenotypes of gene deletion mutant cells exhibiting defects in cell separation. However, no enzymic activity has been demonstrated for PcsB so far. By generating gene deletion mutant strains in four different genetic backgrounds we could demonstrate that pcsB is not essential for cell survival in Streptococcus pneumoniae, but is essential for proper cell division. Deletion mutant cells displayed cluster formation due to aberrant cell division, reduced growth and antibiotic sensitivity that were fully reverted by transformation with a plasmid carrying pcsB. Immunofluorescence staining revealed that PcsB was localized to the cell poles, similarly to PBP3 and LytB, enzymes with demonstrated peptidoglycan-degrading activity required for daughter cell separation. Similarly to other studies with PcsB homologues, we could not detect peptidoglycan-lytic activity with recombinant or native pneumococcal PcsB in vitro. In addition to defects in septum placement and separation, the absence of PcsB induced an increased release of several proteins, such as enolase, MalX and the SP0107 LysM domain protein. Interestingly, genes encoding both LysM domain-containing proteins that are present in the pneumococcal genome (SP0107 and SP2063) and predicted to be involved in cell wall metabolism were found to be highly overexpressed (14-33-fold increase) in ΔpcsB cells in two different genetic backgrounds. Otherwise, we detected very few changes in the global gene expression profile of cells lacking PcsB. Thus our data suggest that LysM domain proteins partially compensate for the lack of PcsB function and allow the survival and slow growth of the pneumococcus.

Downregulation of GbpB, a component of the VicRK regulon, affects biofilm formation and cell surface characteristics of Streptococcus mutans

The virulence of the dental caries pathogen Streptococcus mutans relies in part on the sucrose-dependent synthesis of and interaction with glucan, a major component of the extracellular matrix of tooth biofilms. However, the mechanisms by which secreted and/or cell-associated glucan-binding proteins (Gbps) produced by S. mutans participate in biofilm growth remain to be elucidated. In this study, we further investigate GbpB, an essential immunodominant protein with similarity to murein hydrolases. A conditional knockdown mutant that expressed gbpB antisense RNA under the control of a tetracycline-inducible promoter was constructed in strain UA159 (UACA2) and used to investigate the effects of GbpB depletion on biofilm formation and cell surface-associated characteristics. Additionally, regulation of gbpB by the two-component system VicRK was investigated, and phenotypic analysis of a vicK mutant (UAvicK) was performed. GbpB was directly regulated by VicR, and several phenotypic changes were comparable between UACA2 and UAvicK, although differences between these strains existed. It was established that GbpB depletion impaired initial phases of sucrose-dependent biofilm formation, while exogenous native GbpB partially restored the biofilm phenotype. Several cellular traits were significantly affected by GbpB depletion, including altered cell shape, decreased autolysis, increased cell hydrophobicity, and sensitivity to antibiotics and osmotic and oxidative stresses. These data provide the first experimental evidence for GbpB participation in sucrose-dependent biofilm formation and in cell surface properties.

Identification of Streptococcus suis serotype 2 genes preferentially expressed in the natural host

Streptococcus suis serotype 2 (SS2) is an important zoonotic pathogen for swine and humans. Previous research about the mechanism of SS2 infection was largely established on in vitro or ex vivo models. In this study, we focused on the identification of SS2 genes preferentially expressed in vivo during natural infection in pigs. Eighty SS2 genes were identified to be up-regulated in the porcine brains and lungs by selective capture of transcribed sequences (SCOTS) and comparative dot blot analysis, followed by quantitative RT-PCR validation. These genes could be classified into 5 functional categories: metabolism, cell wall associated proteins, transporters, cell replication, and function unknown. Some of these genes may contribute to the survival and pathogenesis of SS2 in the host via the following strategies. First, SS2 evades the host innate immune clearance through modifying its metabolism and cell wall composition as indicated by the up-regulation of the corresponding gene ldh and pbp2A, respectively. Secondly, SS2 adapts to the in vivo conditions by inducing the expression of the two-component signal transduction system VicKR which may function on the target genes such as pcsB involved in stress response and cell wall biosynthesis. Thirdly, SS2 enhances its virulence in vivo by up-regulating the virulence genes, such as sly, pdgA, ssp, gidA, gcp and hp1311. Further study of these in vivo up-regulated genes will contribute to understanding the in vivo survival mechanism and pathogenesis of SS2.

Cell surface of Lactococcus lactis is covered by a protective polysaccharide pellicle

In Gram-positive bacteria, the functional role of surface polysaccharides (PS) that are not of capsular nature remains poorly understood. Here, we report the presence of a novel cell wall PS pellicle on the surface of Lactococcus lactis. Spontaneous PS-negative mutants were selected using semi-liquid growth conditions, and all mutations were mapped in a single chromosomal locus coding for PS biosynthesis. PS molecules were shown to be composed of hexasaccharide phosphate repeating units that are distinct from other bacterial PS. Using complementary atomic force and transmission electron microscopy techniques, we showed that the PS layer forms an outer pellicle surrounding the cell. Notably, we found that this cell wall layer confers a protective barrier against host phagocytosis by murine macrophages. Altogether, our results suggest that the PS pellicle could represent a new cell envelope structural component of Gram-positive bacteria.

Streptococcus mutans autolysin AtlA is a fibronectin-binding protein and contributes to bacterial survival in the bloodstream and virulence for infective endocarditis

Streptococcus mutans, a commensal of the human oral cavity, can survive in the bloodstream and cause infective endocarditis (IE). However, the virulence factors associated with this manifestation of disease are not known. Here, we demonstrate that AtlA, an autolysin of S. mutans is a newly identified fibronectin (Fn) binding protein and contributes to bacterial resistance to phagocytosis and survival in the bloodstream. Interestingly, prior exposure to plasma at low concentrations was sufficient to enhance bacterial survival in the circulation. Calcium ions at physiological plasma concentrations induced maturation of AtlA from the 104-90 kDa isoform resulting in increased Fn binding and resistance to phagocytosis. An isogenic mutant strain defective in AtlA expression exhibited reduced survival and virulence when tested in a rat model of IE compared with the wild-type and complemented strains. The data presented suggest that plasma components utilized by S. mutans enhanced survival in the circulation and AtlA is a virulence factor associated with infective endocarditis.

Surface plasmon resonance analysis of ricin binding to plasma membranes isolated from NIH 3T3 cells

As the potential for bioterrorism has appeared to increase, the need for simple systems for identifying potential inhibitors of the binding of such biological agents to cell membranes has increased. In this work, surface plasmon resonance (SPR) was used to monitor binding of ricin, a ribosome-inactivating protein, to the plasma membranes of NIH 3T3 cells. Once conditions were established, efficacy of the system for monitoring effectiveness of compounds at inhibiting ricin binding was ascertained by determining the IC(50) values for asialofetuin (ASF) and for bovine serum albumin derivatized with an average of 34 lactosyl moieties (BSA-Lac(34)). Results indicated that SPR is an efficient method for measuring adherence of a toxin to isolated cell plasma membranes. SPR can also indicate whether a compound that is an effective inhibitor of binding when a single ligand such as ASF is used will be as effective when used in studies with cells that may express multiple cell surface ligands for ricin and/or the inhibitor.

Influences of capsule on cell shape and chain formation of wild-type and pcsB mutants of serotype 2 Streptococcus pneumoniae

PcsB is a protein of unknown function that plays a critical role in cell division in Streptococcus pneumoniae and other ovococcus species of Streptococcus. We constructed isogenic sets of mutants expressing different amounts of PcsB in laboratory strain R6 and virulent serotype 2 strain D39 to evaluate its cellular roles. Insertion mutagenesis in parent and pcsB(+) merodiploid strains indicated that pcsB is essential in serotype 2 S. pneumoniae. Quantitative Western blotting of wild-type and epitope-tagged PcsB showed that all PcsB was processed into cell-associated and secreted forms of the same molecular mass and that cell-associated PcsB was moderately abundant and present at approximately 4,900 monomers per cell. Controlled expression and complementation experiments indicated that there was a causative relationship between the severity of defects in cell division and decreasing PcsB amount. These experiments also showed that perturbations of expression of the upstream mreCD genes did not contribute to the cell division defects of pcsB mutants and that mreCD could be deleted. Unexpectedly, capsule influenced the cell shape and chain formation phenotypes of the wild-type D39 strain and mutants underexpressing PcsB or deleted for other genes involved in peptidoglycan biosynthesis, such as dacA. Underexpression of PcsB did not result in changes in the amounts or composition of lactoyl-peptides, which were markedly different in the R6 and D39 strains, and there was no correlation between decreased PcsB amount and sensitivity to penicillin. Finally, microarray analyses indicated that underexpression of PcsB may generate a signal that increases expression of the VicRK regulon, which includes pcsB.

The CHAP domain of Cse functions as an endopeptidase that acts at mature septa to promote Streptococcus thermophilus cell separation

Cell separation is dependent on cell wall hydrolases that cleave the peptidoglycan shared between daughter cells. In Streptococcus thermophilus, this step is performed by the Cse protein whose depletion resulted in the formation of extremely long chains of cells. Cse, a natural chimeric enzyme created by domain shuffling, carries at least two important domains for its activity: the LysM expected to be responsible for the cell wall-binding and the CHAP domain predicted to contain the active centre. Accordingly, the localization of Cse on S. thermophilus cell surface has been undertaken by immunogold electron and immunofluorescence microscopies using of antibodies raised against the N-terminal end of this protein. Immunolocalization shows the presence of the Cse protein at mature septa. Moreover, the CHAP domain of Cse exhibits a cell wall lytic activity in zymograms performed with cell walls of Micrococcus lysodeikticus, Bacillus subtilis and S. thermophilus. Additionally, RP-HPLC analysis of muropeptides released from B. subtilis and S. thermophilus cell wall after digestion with the CHAP domain shows that Cse is an endopeptidase. Altogether, these results suggest that Cse is a cell wall hydrolase involved in daughter cell separation of S. thermophilus.

DSA affinity glycoproteome of human liver tissue

Due to the critical roles of glycoproteins in the activities of cells to tissues, mapping of liver glycoproteome may provide valuable basic information for finding disease marker proteins. In this study, Datura Stramonium Agglutinin (DSA) was chosen to enrich N-linked glycoproteins for its broader specificity with tri- or tetra-antennary complex type. DSA affinity glycoproteins' profiles of human liver tissue were generated by two-dimensional electrophoresis (2-DE) followed by glycoprotein staining based on multiplexed proteomics (MP) technology. 64+/-3 (n=3) protein spots were detected and 41 of glycoproteins were identified via peptide mass fingerprinting (PMF) using MALDI-TOF-MS/MS and annotated to IPI databases. Identified glycoproteins definitely take part in the regulation of cell cycle and metabolic processes. The detailed carbohydrate moiety of some glycoproteins might be concluded according to the literatures. The construction of DSA affinity glycoprotein database would contribute to the subsequent research.

Biological functions of glucan-binding protein B of Streptococcus mutans

INTRODUCTION

Streptococcus mutans has been implicated as a major causative agent of dental caries in humans. Bacterial components associated with the adhesion phase of S. mutans include glucosyltransferases, protein antigen C and proteins that bind glucan. At least four glucan-binding proteins (Gbp) have been identified; GbpA, GbpB, GbpC and GbpD.

METHODS

In our previous study, the contributions of GbpA and GbpC to the virulence of S. mutans were investigated; however, the biological function of GbpB and its role in the virulence of S. mutans remain to be elucidated. Using a GbpB-deficient mutant strain (BD1), we demonstrated in the present study that GbpB has a role in the biology of S. mutans.

RESULTS

The growth rate of BD1 was lower than that of other strains, while it was also shown to be less susceptible to phagocytosis and to form longer chains than the parental strain MT8148. In addition, electron microscope observations of the cell surfaces of BD1 showed that the cell-wall layers were obscure.

CONCLUSION

These results suggest that GbpB may have an important role in cell-wall construction and be involved in cell separation and cell maintenance.

Involvement of sensor kinases in the stress tolerance response of Streptococcus mutans

The gram-positive bacterium Streptococcus mutans is the primary causative agent in the formation of dental caries in humans. The ability of S. mutans to adapt and to thrive in the hostile environment of the oral cavity suggests that this cariogenic pathogen is capable of sensing and responding to different environmental stimuli. This prompted us to investigate the role of two-component signal transduction systems (TCS), particularly the sensor kinases, in response to environmental stresses. Analysis of the annotated genome sequence of S. mutans indicates the presence of 13 putative TCS. Further bioinformatics analysis in our laboratory has identified an additional TCS in the genome of S. mutans. We verified the presence of the 14 sensor kinases by using PCR and Southern hybridization in 13 different S. mutans strains and found that not all of the sensor kinases are encoded by each strain. To determine the potential role of each TCS in the stress tolerance of S. mutans UA159, insertion mutations were introduced into the genes encoding the individual sensor kinases. We were successful in inactivating all of the sensor kinases, indicating that none of the TCS are essential for the viability of S. mutans. The mutant S. mutans strains were assessed for their ability to withstand various stresses, including osmotic, thermal, oxidative, and antibiotic stress, as well as the capacity to produce mutacin. We identified three sensor kinases, Smu486, Smu1128, and Smu1516, which play significant roles in stress tolerance of S. mutans strain UA159.

One of two gbpC gene homologues is involved in dextran-dependent aggregation of Streptococcus sobrinus

INTRODUCTION

Streptococcus sobrinus exhibits marked dextran-dependent aggregation mediated by glucan-binding proteins (GBPs). In contrast to Streptococcus mutans, in which the gbpC gene responsible for dextran-dependent aggregation of this organism has been characterized, genes encoding the S. sobrinus GBPs have not yet been identified.

METHODS

Recently, we identified the gbpC gene homologue from Streptococcus macacae using polymerase chain reaction primers based on the conserved regions of the gbpC sequence exhibiting intraspecies variations. This method was applied to amplify a S. sobrinus homologue.

RESULTS

Unexpectedly, two gbpC gene homologues were identified in S. sobrinus strain 100-4. One homologue, named gbpC, was more similar to the S. mutans gbpC gene than the other and was approximately half the molecular size of its homologue with similar regions interrupted by several non-similar stretches. However, the dextran-binding activity of the protein expressed from gbpC in Escherichia coli was not detected in contrast to the other homologue, a protein designated as Dbl, expressing this activity. The gbpC gene was shown to be intact on the chromosome of strain OMZ176, which does not exhibit dextran-dependent aggregation, while the dbl gene of this strain contained a single adenine nucleotide insertion at approximately one-third the distance from the 5'-end. The insertion mutation in the dbl gene resulted in translation of a premature protein missing its LPXTG sequence signature sequence of the wall-anchored proteins.

CONCLUSION

These results suggest that the dbl gene is very likely responsible for S. sobrinus dextran-dependent aggregation.

Role of peptidoglycan amidases in the development and morphology of the division septum in Escherichia coli

Escherichia coli contains multiple peptidoglycan-specific hydrolases, but their physiological purposes are poorly understood. Several mutants lacking combinations of hydrolases grow as chains of unseparated cells, indicating that these enzymes help cleave the septum to separate daughter cells after cell division. Here, we confirm previous observations that in the absence of two or more amidases, thickened and dark bands, which we term septal peptidoglycan (SP) rings, appear at division sites in isolated sacculi. The formation of SP rings depends on active cell division, and they apparently represent a cell division structure that accumulates because septal synthesis and hydrolysis are uncoupled. Even though septal constriction was incomplete, SP rings exhibited two properties of mature cell poles: they behaved as though composed of inert peptidoglycan, and they attracted the IcsA protein. Despite not being separated by a completed peptidoglycan wall, adjacent cells in these chains were often compartmentalized by the inner membrane, indicating that cytokinesis could occur in the absence of invagination of the entire cell envelope. Finally, deletion of penicillin-binding protein 5 from amidase mutants exacerbated the formation of twisted chains, producing numerous cells having septa with abnormal placements and geometries. The results suggest that the amidases are necessary for continued peptidoglycan synthesis during cell division, that their activities help create a septum having the appropriate geometry, and that they may contribute to the development of inert peptidoglycan.

Localization of PcsB of Streptococcus pneumoniae and its differential expression in response to stress

PcsB of Streptococcus pneumoniae is an essential hydrolase involved in the separation of dividing cells. In this study, it was found that PcsB localizes to the plasma membrane and is released into the growth environment, yet it is detectable on the pneumococcal surface by flow cytometry analysis. High temperature and osmolarity led to upregulation of pcsB expression.

The predicted secretome of Lactobacillus plantarum WCFS1 sheds light on interactions with its environment

The predicted extracellular proteins of the bacterium Lactobacillus plantarum were analysed to gain insight into the mechanisms underlying interactions of this bacterium with its environment. Extracellular proteins play important roles in processes ranging from probiotic effects in the gastrointestinal tract to degradation of complex extracellular carbon sources such as those found in plant materials, and they have a primary role in the adaptation of a bacterium to changing environmental conditions. The functional annotation of extracellular proteins was improved using a wide variety of bioinformatics methods, including domain analysis and phylogenetic profiling. At least 12 proteins are predicted to be directly involved in adherence to host components such as collagen and mucin, and about 30 extracellular enzymes, mainly hydrolases and transglycosylases, might play a role in the degradation of substrates by L. plantarum to sustain its growth in different environmental niches. A comprehensive overview of all predicted extracellular proteins, their domains composition and their predicted function is provided through a database at http://www.cmbi.ru.nl/secretome which could serve as a basis for targeted experimental studies into the function of extracellular proteins.

Streptococcus mutans glucan-binding protein-A affects Streptococcus gordonii biofilm architecture

The glucan-binding protein-A (GbpA) of Streptococcus mutans has been shown to contribute to the architecture of glucan-dependent biofilms formed by this species and influence virulence in a rat model. As S. mutans synthesizes multiple glucosyltransferases and nonglucosyltransferase glucan-binding proteins (GBPs), it is possible that there is functional redundancy that overshadows the full extent of GbpA contributions to S. mutans biology. Glucan-associated properties such as adhesion, aggregation, and biofilm formation were examined independently of other S. mutans GBPs by cloning the gbpA gene into a heterologous host, Streptococcus gordonii, and derivatives with altered or diminished glucosyltransferase activity. The presence of GbpA did not alter dextran-dependent aggregation nor the initial sucrose-dependent adhesion of S. gordonii. However, expression of GbpA altered the biofilm formed by wild-type S. gordonii as well as the biofilm formed by strain CH107 that produced primarily alpha-1,6-linked glucan. Expression of gbpA did not alter the biofilm formed by strain DS512, which produced significantly lower quantities of parental glucan. These data are consistent with a role for GbpA in facilitating the development of biofilms that harbor taller microcolonies via binding to alpha-1,6-linkages within glucan. The magnitude of the GbpA effect appears to be dependent on the quantity and linkage of available glucan.

Glucan-binding proteins are essential for shaping Streptococcus mutans biofilm architecture

Glucan plays a central role in sucrose-dependent biofilm formation by the dental pathogen Streptococcus mutans. This organism synthesizes several proteins capable of binding glucan. These are divided into the glucosyltransferases that catalyze the synthesis of glucan and the nonglucosyltransferase glucan-binding proteins (Gbps). The biological significance of the Gbps has not been thoroughly defined, but studies suggest that these proteins influence virulence and play a role in maintaining biofilm architecture by linking bacteria and extracellular molecules of glucan. We engineered a panel of Gbp mutants, targeting GbpA, GbpC, and GbpD, in which each gene encoding a Gbp was deleted individually and in combination. These strains were then analyzed by confocal microscopy and the biofilm properties were quantified by the biofilm quantification software comstat. All biofilms produced by mutant strains lost significant depth, but the basis for the reduction in height depended on which particular Gbp was missing. The loss of the cell-bound GbpC appeared dominant as might be expected based on losing the principal receptor for glucan. The loss of an extracellular Gbp, either GbpA or GbpD, also profoundly changed the biofilm architecture, each in a unique manner.

The atlA operon of Streptococcus mutans: role in autolysin maturation and cell surface biogenesis

The Smu0630 protein (AtlA) was recently shown to be involved in cell separation, biofilm formation, and autolysis. Here, transcriptional studies revealed that atlA is part of a multigene operon under the control of at least three promoters. The morphology and biofilm-forming capacity of a nonpolar altA mutant could be restored to that of the wild-type strain by adding purified AtlA protein to the medium. A series of truncated derivatives of AtlA revealed that full activity required the C terminus and repeat regions. AtlA was cell associated and readily extractable from with sodium dodecyl sulfate. Of particular interest, the surface protein profile of AtlA-deficient strains was dramatically altered compared to the wild-type strain, as was the nature of the association of the multifunctional adhesin P1 with the cell wall. In addition, AtlA-deficient strains failed to develop competence as effectively as the parental strain. Mutation of thmA, which can be cotranscribed with atlA and encodes a putative pore-forming protein, resulted in a phenotype very similar to that of the AtlA-deficient strain. ThmA was also shown to be required for efficient processing of AtlA to its mature form, and treatment of the thmA mutant strain with full-length AtlA protein did not restore normal cell separation and biofilm formation. The effects of mutating other genes in the operon on cell division, biofilm formation, or AtlA biogenesis were not as profound. This study reveals that AtlA is a surface-associated protein that plays a critical role in the network connecting cell surface biogenesis, biofilm formation, genetic competence, and autolysis.

Functional analysis of glucan binding protein B from Streptococcus mutans

Mutans streptococci are major etiological agents of dental caries, and several of their secreted products contribute to bacterial accumulation on teeth. Of these, Streptococcus mutans glucan binding protein B (GbpB) is a novel, immunologically dominant protein. Its biological function is unclear, although GbpB shares homology with a putative peptidoglycan hydrolase from S. agalactiae and S. pneumoniae, indicative of a role in murein biosynthesis. To determine the cellular function of GbpB, we used several approaches to inactivate the gene, analyze its expression, and identify interacting proteins. None of the transformants analyzed were true gbpB mutants, since they all contained both disrupted and wild-type gene copies, and expression of functional GbpB was always conserved. Thus, the inability to obtain viable gbpB null mutants supports the notion that gbpB is an essential gene. Northern blot and real-time PCR analyses suggested that induction of gbpB expression in response to stress was a strain-dependent phenomenon. Proteins that interacted with GbpB were identified in pull-down and coimmunoprecipitation assays, and these data suggest that GbpB interacts with ribosomal protein L7/L12, possibly as part of a protein complex involved in peptidoglycan synthesis and cell division.

Defects in ex vivo and in vivo growth and sensitivity to osmotic stress of group A Streptococcus caused by interruption of response regulator gene vicR

The regulator VicR of the two-component regulatory system VicRK is essential in several Gram-positive bacteria. However, the authors were able to generate an unconditional vicR insertional mutant of group A Streptococcus. This mutant grew well in rich media but not in non-immune human blood and serum, had attenuated virulence, and was unstable in mice. Complementation of the mutant with vicR expressed in trans restored its phenotype to wild-type. A vicK deletion mutant had a phenotype similar to that of the vicR mutant. Phagocytosis and killing of the vicR mutant were normal, suggesting that VicRK does not regulate processes involved in evasion of host defence. Microarray analysis showed that vicR inactivation down-regulated the transcription of 13 genes, including putative cell wall hydrolase gene pcsB and spy1058-1060, which encode a putative phosphotransferase system enzyme II for carbohydrate transport, and upregulated the expression of five genes, including spy0183 and spy0184, which encode an osmoprotectant transporter OpuA. Consistent with microarray analysis, the vicR mutant took up more of the osmoprotectants betaine and proline and was sensitive to osmotic stress, indicating that vicR inactivation induced osmotic stress and increased susceptibility to osmotic pressure. Additionally, a spy1060 deletion mutant also displayed attenuated virulence. These results suggest that VicRK regulates processes involved in cell wall metabolism, nutrient uptake, and osmotic protection.

Pseudomonas aeruginosa 1244 pilin glycosylation: glycan substrate recognition

The pilin of Pseudomonas aeruginosa 1244 is glycosylated with an oligosaccharide that is structurally identical to the O-antigen repeating unit of this organism. Concordantly, the metabolic source of the pilin glycan is the O-antigen biosynthetic pathway. The present study was conducted to investigate glycan substrate recognition in the 1244 pilin glycosylation reaction. Comparative structural analysis of O subunits that had been previously shown to be compatible with the 1244 glycosylation machinery revealed similarities among sugars at the presumed reducing termini of these oligosaccharides. We therefore hypothesized that the glycosylation substrate was within the sugar at the reducing end of the glycan precursor. Since much is known of PA103 O-antigen genetics and because the sugars at the reducing termini of the O7 (strain 1244) and O11 (strain PA103) are identical (beta-N-acetyl fucosamine), we utilized PA103 and strains that express lipopolysaccharide (LPS) with a truncated O-antigen subunit to test our hypothesis. LPS from a strain mutated in the wbjE gene produced an incomplete O subunit, consisting only of the monosaccharide at the reducing end (beta-d-N-acetyl fucosamine), indicating that this moiety contained substrate recognition elements for WaaL. Expression of pilAO(1244) in PA103 wbjE::aacC1, followed by Western blotting of extracts of these cells, indicated that pilin produced has been modified by the addition of material consistent with a single N-acetyl fucosamine. This was confirmed by analyzing endopeptidase-treated pilin by mass spectrometry. These data suggest that the pilin glycosylation substrate recognition features lie within the reducing-end moiety of the O repeat and that structures of the remaining sugars are irrelevant.

The response regulator CroR modulates expression of the secreted stress-induced SalB protein in Enterococcus faecalis

The Enterococcus faecalis two-component signal transduction system CroRS, also referred as the RR-HK05 pair, is required for intrinsic beta-lactam resistance (Y. R. Comenge, R. Quintiliani, Jr., L. Li, L. Dubost, J. P. Brouard, J. E. Hugonnet, and M. Arthur, J. Bacteriol. 185:7184-7192, 2003) and is also suspected to be involved in the expression of salB (previously referred to as sagA), a gene important for resistance to environmental stress and cell morphology (Y. Le Breton, G. Boël, A. Benachour, H. Prévost, Y. Auffray, and A. Rincé, Environ. Microbiol. 5:329-337, 2003). In this report, we provide genetic and biochemical evidence that salB encodes a secreted protein that is expressed from a monocistronic stress-inducible operon. Consistent with CroR being a direct transcriptional activator of the salB expression, CroR was found to bind to the salB promoter region in electrophoretic mobility shift assays. Interestingly, we provide evidence that SalB does not play a role in the intrinsic beta-lactam resistance associated with CroRS. We also show that the CroRS system is able to regulate its own expression. The sequence of the CroRS binding site in the salB and croR promoter regions was determined using DNase I footprinting assays.

Glucosyltransferases of viridans group streptococci modulate interleukin-6 and adhesion molecule expression in endothelial cells and augment monocytic cell adherence

Recruitment of monocytes plays important roles during vegetation formation and endocardial inflammation in the pathogenesis of infective endocarditis (IE). Bacterial antigens or modulins can activate endothelial cells through the expression of cytokines or adhesion molecules and modulate the recruitment of leukocytes. We hypothesized that glucosyltransferases (GTFs), modulins of viridans group streptococci, may act directly to up-regulate the expression of adhesion molecules and also interleukin-6 (IL-6) to augment monocyte attachment to endothelial cells. Using primary cultured human umbilical vein endothelial cells (HUVECs) as an in vitro model, we demonstrated that GTFs (in the cell-bound or free form) could specifically modulate the expression of IL-6, and also adhesion molecules, in a dose- and time-dependent manner. Results of inhibition assays suggested that enhanced expression of adhesion molecules was dependent on the activation of nuclear factor kappaB (NF-kappaB) and extracellular signal-regulated kinase and that p38 mitogen-activated protein kinase pathways also contributed to the release of IL-6. Streptococcus-infected HUVECs or treatment with purified IL-6 plus soluble IL-6 receptor alpha enhanced the expression of ICAM-1 and the adherence of the monocytic cell line U937. These results suggest that streptococcal GTFs might play an important role in recruiting monocytic cells during inflammation in IE through induction of adhesion molecules and IL-6, a cytokine involved in transition from neutrophil to monocyte recruitment.

Bactericidal effects of diode laser onStreptococcus mutans after irradiation through different thickness of dentin

BACKGROUND AND OBJECTIVES

A reliable method to eradicate the bacteria of residual carious dentin has not yet been developed. The aim of this study was to evaluate the antibacterial effect of a diode laser on Streptococcus mutans through different thickness (500, 1,000, and 2,000 microm) of human dentin. The thermal effect of laser irradiation was also investigated.

STUDY DESIGN/MATERIALS AND METHODS

Dentin specimens were inoculated with 2 microl of S. mutans on one side and irradiated by a diode laser on the other side with a power output ranging from 0.5 to 7 W. The laser tip was swept with the whole irradiation area of 7 mm x 3 mm at a speed of about 10 mm/second with a total irradiation time of 30 seconds. Cooling with distilled water (30 ml/minute) was applied simultaneously during laser irradiation. After laser irradiation, the bacteria was removed from the dentin surfaces and cultured for 48 hours at 37 degrees C anaerobically to assess the colony forming units (CFU) per ml. The morphology of the lased bacteria and the temperature rise during laser irradiation were observed by scanning electron microscope (SEM) and measured by thermocouple, respectively.

RESULTS

The results revealed that 7 W of laser power could kill 97.7% of CFU through 500 microm thickness of dentin. However, the bactericidal efficiency was significantly reduced as the dentin thickness was increased. The morphological changes of lased bacteria ranged from less affected such as loss of their wall bands and existence of minicells to more severely degenerated, such as disintegration and fusion of cells with pores on the cell wall. Only the dentin specimens with a thickness of 500 microm exhibited a temperature rise greater than 5.5 degrees C after receiving 5 or 7 W of laser irradiation.

CONCLUSIONS

A diode laser can eliminate the Streptococcus mutans of the residual carious dentin without inducing high pulpal temperature rise when the remaining dentin thickness is greater than 1 mm.

Glycosylation substrate specificity of Pseudomonas aeruginosa 1244 pilin

The beta-carbon of the Pseudomonas aeruginosa 1244 pilin C-terminal Ser is a site of glycosylation. The present study was conducted to determine the pilin structures necessary for glycosylation. It was found that although Thr could be tolerated at the pilin C terminus, the blocking of the Ser carboxyl group with the addition of an Ala prevented glycosylation. Pilin from strain PA103 was not glycosylated by P. aeruginosa 1244, even when the C-terminal residue was converted to Ser. Substituting the disulfide loop region of strain PA103 pilin with that of strain 1244 allowed glycosylation to take place. Neither conversion of 1244 pilin disulfide loop Cys residues to Ala nor the deletion of segments of this structure prevented glycosylation. It was noted that the PA103 pilin disulfide loop environment was electronegative, whereas that of strain 1244 pilin had an overall positive charge. Insertion of a positive charge into the PA103 pilin disulfide loop of a mutant containing Ser at the C terminus allowed glycosylation to take place. Extending the "tail" region of the PA103 mutant pilin containing Ser at its terminus resulted in robust glycosylation. These results suggest that the terminal Ser is the major pilin glycosylation recognition feature and that this residue cannot be substituted at its carboxyl group. Although no other specific recognition features are present, the pilin surface must be compatible with the reaction apparatus for glycosylation to occur.

Characterization of salivary immunoglobulin A responses in children heavily exposed to the oral bacterium Streptococcus mutans: influence of specific antigen recognition in infection

The initial infection of children by Streptococcus mutans, the main pathogen of dental caries, depends on the ability of S. mutans to adhere and accumulate on tooth surfaces. These processes involve the adhesin antigen I/II (AgI/II), glucosyltransferases (GTF) and glucan-binding protein B (GbpB), each a target for anticaries vaccines. The salivary immunoglobulin A (IgA) antibody responses to S. mutans antigens (Ags) were characterized in 21 pairs of 5- to 13-month-old children. Pairs were constructed with one early S. mutans-infected and one noninfected child matched by age, racial background, number of teeth, and salivary levels of IgA. Specific salivary IgA antibody response and S. mutans infection levels were then measured during a 1-year follow-up. Robust responses to S. mutans were detected from 6 months of age. Salivary IgA antibody to AgI/II and GTF was commonly detected in salivas of all 42 children. However, GbpB-specific IgA antibody was seldom detected in the subset of infected children (38.1% at baseline). In contrast, most of the subset of noninfected children (76.2%) showed GbpB-reactive IgA antibody during the same period. Frequencies of GbpB responses increased with age, but differences in intensities of GbpB-IgA antibody reactions were sustained between the subsets. At baseline, GbpB-reactive IgA antibody accounted for at least half of the total salivary IgA S. mutans-reactive antibody in 33.3 and 9.5% of noninfected and infected children, respectively. This study provides evidence that a robust natural response to S. mutans Ags can be achieved by 1 year of age and that IgA antibody specificities may be critical in modulating initial S. mutans infection.

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.

cse, a Chimeric and variable gene, encodes an extracellular protein involved in cellular segregation in Streptococcus thermophilus

The isolation of a Streptococcus thermophilus CNRZ368 mutant displaying a long-chain phenotype allowed us to identify the cse gene (for cellular segregation). The N terminus of Cse exhibits high similarity to Streptococcus agalactiae surface immunogenic protein (SIP), while its C terminus exhibits high similarity to S. thermophilus PcsB. In CNRZ368, deletion of the entire cse open reading frame leads to drastic lengthening of cell chains and altered colony morphology. Complementation of the Deltacse mutation with a wild-type allele restored both wild-type phenotypes. The central part of Cse is a repeat-rich region with low sequence complexity. Comparison of cse from CNRZ368 and LMG18311 strains reveals high variability of this repeat-rich region. To assess the impact of this central region variability, the central region of LMG18311 cse was exchanged with that of CNRZ368 cse. This replacement did not affect chain length, showing that divergence of the central part does not modify cell segregation activity of Cse. The structure of the cse locus suggests that the chimeric organization of cse results from insertion of a duplicated sequence deriving from the pcsB 3' end into an ancestral sip gene. Thus, the cse locus illustrates the module-shuffling mechanism of bacterial gene evolution.

Defective cell wall synthesis in Streptococcus pneumoniae R6 depleted for the essential PcsB putative murein hydrolase or the VicR (YycF) response regulator

PcsB is a protein of unknown function(s) that influences the cell morphology of several pathogenic species of streptococcus. PcsB contains a CHAP (cysteine, histidine-dependent amidohydrolase/peptidase) domain found in bacterial murein hydrolases; however, direct links between steps in cell wall biosynthesis and PcsB function(s) have not been demonstrated. We show here that pcsB is essential in the human respiratory pathogen, Streptococcus pneumoniae, that depletion of PcsB is bacteriostatic and that alanine substitutions in the conserved cysteine and histidine residues of the CHAP domain appear to be lethal. We stained wild-type parent and mutant bacteria deficient in expression of PcsB with fluorescent vancomycin and DAPI to determine patterns of cell wall synthesis and nucleoid segregation respectively. The wild-type parent strain exhibited ordered, simultaneous septal and equatorial cell wall synthesis. In contrast, reduced expression of PcsB resulted in formation of long chains of cells in which peptidoglycan synthesis occurred at nearly every division septum and cell equator. Severe depletion of PcsB led to abnormal, uncontrolled cell wall synthesis at misplaced septa and around large cells. Together, these physiological properties are consistent with a role for PcsB as a murein hydrolase that balances the extent of cell wall synthesis in S. pneumoniae. Finally, we show that the defects in morphology and cell wall synthesis that result from depletion of PcsB strongly resemble those caused by depletion of the essential VicRK two component regulatory system (TCS). This result and the essentiality of pcsB support the hypothesis that the essentiality of the VicRK TCS results from its positive regulation of PcsB expression.

The role of pilin glycan in neisserial pathogenesis

The pilus of pathogenic Neisseria is a polymer composed mainly of the glycoprotein, pilin. Recent investigations significantly enhanced characterization of pilin glycan (Pg) from N. gonorrhoeae (gonococcus, GC) and N. meningitidis (meningococcus, MC). Several pilin glycosylation genes were discovered recently from these bacteria and some of these genes transfer sugars previously unknown to be present in neisserial pili. Due to these findings, glycans of GC and MC pilin are now considered more complex. Furthermore, various Pg can be expressed by different strains and variants of GC, as well as MC. Intra-species variation of Pg between different groups of GC or MC can partly be due to polymorphisms of glycosylation genes. In pilus of pathogenic Neisseria, alternative glycoforms are also produced due to phase-variation (Pv) of pilin glycosylation genes. Most remarkably, the pgtA (pilin glycosyl transferase A) gene of GC can either posses or lack the ability of Pv. Many GC strains carry the phase-variable (Pv+) pgtA, whereas others carry the allele lacking Pv (Pv-). Mostly, the GC isolates from disseminated gonococcal infection (DGI) carry Pv+ pgtA but organisms from uncomplicated gonorrhea (UG) contain the Pv- allele. This data suggests that Pv of pgtA facilitates DGI, whereas constitutive expression of the Pv- pgtA may promote UG. Additional implications of Pg in various physiological and pathogenic mechanisms of Neisseria can also be envisaged based on various recent data.