Nucleotide sequence of the Streptococcus gordonii PK488 coaggregation adhesin gene, scaA, and ATP-binding cassette

Genome characterization and taxonomy of Actinomyces acetigenes sp. nov., and Actinomyces stomatis sp. nov., previously isolated from the human oral cavity

BACKGROUND

Actinomyces strains are commonly found as part of the normal microflora on human tissue surfaces, including the oropharynx, gastrointestinal tract, and female genital tract. Understanding the diversity and characterization of Actinomyces species is crucial for human health, as they play an important role in dental plaque formation and biofilm-related infections. Two Actinomyces strains ATCC 49340 T and ATCC 51655 T have been utilized in various studies, but their accurate species classification and description remain unresolved.

RESULTS

To investigate the genomic properties and taxonomic status of these strains, we employed both 16S rRNA Sanger sequencing and whole-genome sequencing using the Illumina HiSeq X Ten platform with PE151 (paired-end) sequencing. Our analyses revealed that the draft genome of Actinomyces acetigenes ATCC 49340 T was 3.27 Mbp with a 68.0% GC content, and Actinomyces stomatis ATCC 51655 T has a genome size of 3.08 Mbp with a 68.1% GC content. Multi-locus (atpA, rpoB, pgi, metG, gltA, gyrA, and core genome SNPs) sequence analysis supported the phylogenetic placement of strains ATCC 51655 T and ATCC 49340 T as independent lineages. Digital DNA-DNA hybridization (dDDH), average nucleotide identity (ANI), and average amino acid identity (AAI) analyses indicated that both strains represented novel Actinomyces species, with values below the threshold for species demarcation (70% dDDH, 95% ANI and AAI). Pangenome analysis identified 5,731 gene clusters with strains ATCC 49340 T and ATCC 51655 T possessing 1,515 and 1,518 unique gene clusters, respectively. Additionally, genomic islands (GIs) prediction uncovered 24 putative GIs in strain ATCC 49340 T and 16 in strain ATCC 51655 T, contributing to their genetic diversity and potential adaptive capabilities. Pathogenicity analysis highlighted the potential human pathogenicity risk associated with both strains, with several virulence-associated factors identified. CRISPR-Cas analysis exposed the presence of CRISPR and Cas genes in both strains, indicating these strains might evolve a robust defense mechanism against them.

CONCLUSION

This study supports the classification of strains ATCC 49340 T and ATCC 51655 T as novel species within the Actinomyces, in which the name Actinomyces acetigenes sp. nov. (type strain ATCC 49340 T = VPI D163E-3 T = CCUG 34286 T = CCUG 35339 T) and Actinomyces stomatis sp. nov. (type strain ATCC 51655 T = PK606T = CCUG 33930 T) are proposed.

Two Permeases Associated with the Multifunctional CtaP Cysteine Transport System in Listeria monocytogenes Play Distinct Roles in Pathogenesis

The soil-dwelling bacterium Listeria monocytogenes survives a multitude of conditions when residing in the outside environment and as a pathogen within host cells. Key to survival within the infected mammalian host is the expression of bacterial gene products necessary for nutrient acquisition. Similar to many bacteria, L. monocytogenes uses peptide import to acquire amino acids. Peptide transport systems play an important role in nutrient uptake as well as in additional functions that include bacterial quorum sensing and signal transduction, recycling of peptidoglycan fragments, adherence to eukaryotic cells, and alterations in antibiotic susceptibility. It has been previously described that CtaP, encoded by lmo0135, is a multifunctional protein associated with activities that include cysteine transport, resistance to acid, membrane integrity, and bacterial adherence to host cells. ctaP is located next to two genes predicted to encode membrane-bound permeases lmo0136 and lmo0137, termed CtpP1 and CtpP2, respectively. Here, we show that CtpP1 and CtpP2 are required for bacterial growth in the presence of low concentrations of cysteine and for virulence in mouse infection models. Taken together, the data identify distinct nonoverlapping roles for two related permeases that are important for the growth and survival of L. monocytogenes within host cells. IMPORTANCE Bacterial peptide transport systems are important for nutrient uptake and may additionally function in a variety of other roles, including bacterial communication, signal transduction, and bacterial adherence to eukaryotic cells. Peptide transport systems often consist of a substrate-binding protein associated with a membrane-spanning permease. The environmental bacterial pathogen Listeria monocytogenes uses the substrate-binding protein CtaP not only for cysteine transport but also for resistance to acid, maintenance of membrane integrity, and bacterial adherence to host cells. In this study, we demonstrate complementary yet distinct functional roles for two membrane permeases, CtpP1 and CtpP2, that are encoded by genes linked to ctaP and that contribute to bacterial growth, invasion, and pathogenicity.

Peptidomimetics as Potential Anti-Virulence Drugs Against Resistant Bacterial Pathogens

The uncontrollable spread of superbugs calls for new approaches in dealing with microbial-antibiotic resistance. Accordingly, the anti-virulence approach has arisen as an attractive unconventional strategy to face multidrug-resistant pathogens. As an emergent strategy, there is an imperative demand for discovery, design, and development of anti-virulence drugs. In this regard, peptidomimetic compounds could be a valuable source of anti-virulence drugs, since these molecules circumvent several shortcomings of natural peptide-based drugs like proteolytic instability, immunogenicity, toxicity, and low bioavailability. Some emerging evidence points to the feasibility of peptidomimetics to impair pathogen virulence. Consequently, in this review, we shed some light on the potential of peptidomimetics as anti-virulence drugs to overcome antibiotic resistance. Specifically, we address the anti-virulence activity of peptidomimetics against pathogens' secretion systems, biofilms, and quorum-sensing systems.

An intramembrane sensory circuit monitors sortase A-mediated processing of streptococcal adhesins

Bacterial adhesins mediate adhesion to substrates and biofilm formation. Adhesins of the LPXTG family are posttranslationally processed by the cell membrane-localized peptidase sortase A, which cleaves the LPXTG motif. This generates a short C-terminal peptide (C-pep) that remains in the cell membrane, whereas the mature adhesin is incorporated into the cell wall. Genes encoding adhesins of the oral bacterium Streptococcus gordonii were differentially expressed depending on whether the bacteria were isolated from saliva or dental plaque and appeared to be coordinately regulated. Deletion of sspA and sspB (sspAB), both of which encode LPXTG-containing adhesins, unexpectedly enhanced adhesion and biofilm formation. C-peps produced from a model LPXTG-containing adhesin localized to the cell membrane and bound to and inhibited the intramembrane sensor histidine kinase SGO_1180, thus preventing activation of the cognate response regulator SGO_1181. The absence of SspAB C-peps induced the expression of the scaCBA operon encoding the lipoprotein adhesin ScaA, which was sufficient to preserve and even enhance biofilm formation. This C-pep-driven regulatory circuit also exists in pathogenic streptococci and is likely conserved among Gram-positive bacteria. This quality control mechanism ensures that the bacteria can form biofilms under diverse environmental conditions and may play a role in optimizing adhesion and biofilm formation.

The effect of smoking on caries-related microorganisms

INTRODUCTION

Epidemiological studies have shown a close relationship between smoking and dental caries. Bacteria are one of the essential factors of caries formation. The imbalance of cariogenic bacteria and commensal bacteria in dental plaque results in higher production of acid that can corrode dental hard tissue. The aim of our review is to summarize the effect of smoking on caries-related bacteria.

METHODS

English articles available in Pubmed and ScienceDirect databases and published before December 2018 were searched. A variety of evidence was collected including not only the influence of cigarette products on bacteria strains in vitro but also their effect on bacterial composition in saliva and dental plaque in vivo. We particularly emphasize the mechanisms by which nicotine acts on oral bacteria.

RESULTS

The components of cigarettes promote the growth of cariogenic microorganisms. The mechanisms of how nicotine enhances Streptococcus mutans, Lactobacilli, Streptococcus gordonii, Actinomyces and Candida albicans are described separately in detail. The commensal bacteria, Streptococcus sanguinis, show less competitive capability in the presence of nicotine. Smoking influences saliva by lowering the buffer capability, altering its chemical agent and bacterial components, and therefore promotes the formation of a caries-susceptible environment.

CONCLUSIONS

Cigarette smoking and nicotine exposure promote the cariogenic activity of oral microorganisms and the formation of a caries-susceptible environment. This suggests that smokers should quit smoking, amongst other health reasons, also for their oral health.

Molecular pathways underlying inhibitory effect of antimicrobial peptide Nal-P-113 on bacteria biofilms formation of Porphyromonas gingivalis W83 by DNA microarray

Background

Wound-related infection remains a major challenge for health professionals. One disadvantage in conventional antibiotics is their inability to penetrate biofilms, the main protective strategy for bacteria to evade irradiation. Previously, we have shown that synthetic antimicrobial peptides could inhibit bacterial biofilms formation.

Results

In this study, we first delineated how Nal-P-113, a novel antimicrobial peptide, exerted its inhibitory effects on Porphyromonas gingivalis W83 biofilms formation at a low concentration. Secondly, we performed gene expression profiling and validated that Nal-P-113 at a low dose significantly down-regulated genes related to mobile and extrachromosomal element functions, transport and binding proteins in Porphyromonas gingivalis W83.

Conclusions

These findings suggest that Nal-P-113 at low dose is sufficient to inhibit the formation of biofilms although Porphyromonas gingivalis W83 may maintain its survival in the oral cavity. The newly discovered molecular pathways may add the knowledge of developing a new strategy to target bacterial infections in combination with current first-line treatment in periodontitis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-017-0948-z) contains supplementary material, which is available to authorized users.

Contribution of Streptococcus gordonii Hsa Adhesin to Biofilm Formation

Adhesion of oral mitis group streptococci, such as Streptococcus gordonii, to acquired pellicle on the tooth surface is the first step in oral biofilm formation. S. gordonii strain DL1 possesses an Hsa adhesin, which recognizes the terminal sialic acid of host sialoglycoconjugates. The aim of the present study was to investigate the role of the Hsa adhesin in biofilm formation. The biofilm-forming ability of a S. gordonii hsa mutant on microtiter plates pre-coated with saliva, fetuin, or mucin was significantly lower than that of wild-type strain DL1. In contrast, no significant difference in biofilm-forming ability was observed in plates pre-coated with bovine serum albumin, which does not contain sialic acid. The biofilm-forming ability of strain DL1 in saliva-coated microtiter plates was also significantly reduced when the plate was pre-treated with neuraminidase. The sialic acid-dependent biofilm-forming ability of different wild-type S. gordonii strains varied. However, Southern and western blot analyses showed that all the tested wild-type strains possessed and expressed hsa homologs, respectively. These results indicate that the binding of Hsa adhesin to sialoglycoconjugates is associated with biofilm formation of S. gordonii DL1, and imply variation in the contribution of Hsa and its homologs to S. gordonii biofilm formation.

Effects of Nicotine on Streptococcus gordonii Growth, Biofilm Formation, and Cell Aggregation

Streptococcus gordonii is a commensal species of human oral flora. It initiates dental biofilm formation and provides binding sites for later colonizers to attach to and generate mature biofilm. Smoking is the second highest risk factor for periodontal disease, and cigarette smoke extract has been reported to facilitate Porphyromonas gingivalis-S. gordonii dual-species biofilm formation. Our hypothesis is that nicotine, one of the most important and active components of tobacco, stimulates S. gordonii multiplication and aggregation. In the present study, S. gordonii planktonic cell growth (kinetic absorbance and CFU), biofilm formation (crystal violet stain and confocal laser scanning microscopy [CLSM]), aggregation with/without sucrose, and 11 genes that encode binding proteins or regulators of gene expression were investigated. Results demonstrated planktonic cell growth was stimulated by 1 to 4 mg/ml nicotine treatment. Biofilm formation was increased at 0.5 to 4 mg/ml nicotine. CLSM indicated bacterial cell mass was increased by 2 and 4 mg/ml nicotine, but biofilm extracellular polysaccharide was not significantly affected by nicotine. Cell aggregation was upregulated by 4, 8, and 16 mg/ml nicotine with sucrose and by 16 mg/ml nicotine without sucrose. Quantitative reverse transcriptase PCR indicated S. gordonii abpA, scaA, ccpA, and srtA were upregulated in planktonic cells by 2 mg/ml nicotine. In conclusion, nicotine stimulates S. gordonii planktonic cell growth, biofilm formation, aggregation, and gene expression of binding proteins. Those effects may promote later pathogen attachment to tooth surfaces, the accumulation of tooth calculus, and the development of periodontal disease in cigarette smokers.

Intercellular communications in multispecies oral microbial communities

The oral cavity contains more than 700 microbial species that are engaged in extensive cell–cell interactions. These interactions contribute to the formation of highly structured multispecies communities, allow them to perform physiological functions, and induce synergistic pathogenesis. Co-adhesion between oral microbial species influences their colonization of oral cavity and effectuates, to a large extent, the temporal and spatial formation of highly organized polymicrobial community architecture. Individual species also compete and collaborate with other neighboring species through metabolic interactions, which not only modify the local microenvironment such as pH and the amount of oxygen, making it more suitable for the growth of other species, but also provide a metabolic framework for the participating microorganisms by maximizing their potential to extract energy from limited substrates. Direct physical contact of bacterial species with its neighboring co-habitants within microbial community could initiate signaling cascade and achieve modulation of gene expression in accordance with different species it is in contact with. In addition to communication through cell–cell contact, quorum sensing (QS) mediated by small signaling molecules such as competence-stimulating peptides (CSPs) and autoinducer-2 (AI-2), plays essential roles in bacterial physiology and ecology. This review will summarize the evidence that oral microbes participate in intercellular communications with co-inhabitants through cell contact-dependent physical interactions, metabolic interdependencies, as well as coordinative signaling systems to establish and maintain balanced microbial communities.

The Expression of the fim Operon Is Crucial for the Survival of Streptococcus parasanguinis FW213 within Macrophages but Not Acid Tolerance

The acquisition of transition metal ions is essential for the viability and in some cases the expression of virulence genes in bacteria. The fimCBA operon of Streptococcus parasanguinis FW213 encodes a Mn²⁺/Fe²⁺-specific ATP-binding cassette transporter. FimA, a lipoprotein in the system, is essential for the development of endocarditis, presumably by binding to fibrin monolayers on the damaged heart tissue. Recent sequence analysis revealed that Spaf_0344 was homologous to Streptococcus gordonii scaR, encoding a metalloregulatory protein for the Sca Mn²⁺-specific transporter. Based on the homology, Spaf_0344 was designated fimR. By using various fim promoter (p_fim) derivatives fused with a promoterless chloramphenicol acetyltransferase gene, the functions of the cis-elements of p_fim were analyzed in the wild-type and fimR-deficient hosts. The result indicated that FimR represses the expression of p_fim and the palindromic sequences 5′ to fimC are involved in repression of p_fim. A direct interaction between FimR and the palindromic sequences was further confirmed by in vitro electrophoresis gel mobility shift assay and in vivo chromatin immunoprecipitation assay (ChIP)-quantitative real-time PCR (qPCR). The result of the ChIP-qPCR analysis also indicated that FimR is activated by Mn²⁺ and, to a lesser degree, Fe²⁺. Functional analysis indicated that the expression of FimA in S. parasanguinis was critical for wild-type levels of survival against oxidative stress and within phagocytes, but not for acid tolerance. Taken together, in addition to acting as an adhesin (FimA), the expression of the fim operon is critical for the pathogenic capacity of S. parasanguinis.

Improved adhesive properties of recombinant bifidobacteria expressing the Bifidobacterium bifidum-specific lipoprotein BopA

Background

Bifidobacteria belong to one of the predominant bacterial groups in the intestinal microbiota of infants and adults. Several beneficial effects on the health status of their human hosts have been demonstrated making bifidobacteria interesting candidates for probiotic applications. Adhesion of probiotics to the intestinal epithelium is discussed as a prerequisite for colonisation of and persistence in the gastrointestinal tract.

Results

In the present study, 15 different strains of bifidobacteria were tested for adhesion. B. bifidum was identified as the species showing highest adhesion to all tested intestinal epithelial cell (IEC) lines. Adhesion of B. bifidum S17 to IECs was strongly reduced after treatment of bacteria with pronase. These results strongly indicate that a proteinaceous cell surface component mediates adhesion of B. bifidum S17 to IECs. In silico analysis of the currently accessible Bifidobacterium genomes identified bopA encoding a lipoprotein as a B. bifidum-specific gene previously shown to function as an adhesin of B. bifidum MIMBb75. The in silico results were confirmed by Southern Blot analysis. Furthermore, Northern Blot analysis demonstrated that bopA is expressed in all B. bifidum strains tested under conditions used to cultivate bacteria for adhesion assays. The BopA gene was successfully expressed in E. coli and purified by Ni-NTA affinity chromatography as a C-terminal His₆-fusion. Purified BopA had an inhibitory effect on adhesion of B. bifidum S17 to IECs. Moreover, bopA was successfully expressed in B. bifidum S17 and B. longum/infantis E18. Strains overexpressing bopA showed enhanced adhesion to IECs, clearly demonstrating a role of BopA in adhesion of B. bifidum strains.

Conclusions

BopA was identified as a B. bifidum-specific protein involved in adhesion to IECs. Bifidobacterium strains expressing bopA show enhanced adhesion. Our results represent the first report on recombinant bifidobacteria with improved adhesive properties.

Sequencing and comparative genome analysis of two pathogenic Streptococcus gallolyticus subspecies: genome plasticity, adaptation and virulence

Streptococcus gallolyticus infections in humans are often associated with bacteremia, infective endocarditis and colon cancers. The disease manifestations are different depending on the subspecies of S. gallolyticus causing the infection. Here, we present the complete genomes of S. gallolyticus ATCC 43143 (biotype I) and S. pasteurianus ATCC 43144 (biotype II.2). The genomic differences between the two biotypes were characterized with comparative genomic analyses. The chromosome of ATCC 43143 and ATCC 43144 are 2,36 and 2,10 Mb in length and encode 2246 and 1869 CDS respectively. The organization and genomic contents of both genomes were most similar to the recently published S. gallolyticus UCN34, where 2073 (92%) and 1607 (86%) of the ATCC 43143 and ATCC 43144 CDS were conserved in UCN34 respectively. There are around 600 CDS conserved in all Streptococcus genomes, indicating the Streptococcus genus has a small core-genome (constitute around 30% of total CDS) and substantial evolutionary plasticity. We identified eight and five regions of genome plasticity in ATCC 43143 and ATCC 43144 respectively. Within these regions, several proteins were recognized to contribute to the fitness and virulence of each of the two subspecies. We have also predicted putative cell-surface associated proteins that could play a role in adherence to host tissues, leading to persistent infections causing sub-acute and chronic diseases in humans. This study showed evidence that the S. gallolyticus still possesses genes making it suitable in a rumen environment, whereas the ability for S. pasteurianus to live in rumen is reduced. The genome heterogeneity and genetic diversity among the two biotypes, especially membrane and lipoproteins, most likely contribute to the differences in the pathogenesis of the two S. gallolyticus biotypes and the type of disease an infected patient eventually develops.

Identification of horizontal gene transfer and recombination of PsaA gene in streptococcus mitis group

Pneumococcal surface adhesin A (psaA) gene is universally confirmed as one of the Streptococcus pneumoniae adhesion genes, but it is disputed whether the psaA gene is a Streptococcus pneumoniae species-specific gene. In the present study, the presence of the psaA gene in 34 streptococcus mitis group isolates was identified by the PCR approach and a comparison of sequencing PCR products (Streptococcus pneumoniae R6 as the control strain). Also, the evolutionary scenarios of these psaA genes in these streptococcus mitis group isolates were analyzed by a phylogenetic tree based on the housekeeping genes (sodA and rnpB) and psaA genes. As a result, a high degree of conservation of open reading frame sequences in all six Streptococcus pneumoniae strains (100% similarity) and in the other species of the streptococcus mitis group (92.6-100% similarity) was revealed. Further genetics research based on housekeeping genes and psaA gene phylogenies showed that the psaA gene was of vertical inheritance only in Streptococcus pneumoniae; however, high-frequency horizontal psaA gene transfer and recombination occurred in the other species of the streptococcus mitis group. These findings confirmed that the psaA gene was not a Streptococcus pneumoniae species-specific gene, and high-frequency HGT and recombination events may explain the presence of the psaA gene in the other species of the streptococcus mitis group.

Listeria monocytogenes CtaP is a multifunctional cysteine transport-associated protein required for bacterial pathogenesis

The bacterial pathogen Listeria monocytogenes survives under a myriad of conditions in the outside environment and within the human host where infections can result in severe disease. Bacterial life within the host requires the expression of genes with roles in nutrient acquisition as well as the biosynthesis of bacterial products required to support intracellular growth. A gene product identified as the substrate-binding component of a novel oligopeptide transport system (encoded by lmo0135) was recently shown to be required for L. monocytogenes virulence. Here we demonstrate that lmo0135 encodes a multifunctional protein that is associated with cysteine transport, acid resistance, bacterial membrane integrity and adherence to host cells. The lmo0135 gene product (designated CtaP, for cysteine transport associated protein) was required for bacterial growth in the presence of low concentrations of cysteine in vitro, but was not required for bacterial replication within the host cytosol. Loss of CtaP increased membrane permeability and acid sensitivity, and reduced bacterial adherence to host cells. ctaP deletion mutants were severely attenuated following intragastric and intravenous inoculation of mice. Taken together, the data presented indicate that CtaP contributes to multiple facets of L. monocytogenes physiology, growth and survival both inside and outside of animal cells.

Streptococcus adherence and colonization

Streptococci readily colonize mucosal tissues in the nasopharynx; the respiratory, gastrointestinal, and genitourinary tracts; and the skin. Each ecological niche presents a series of challenges to successful colonization with which streptococci have to contend. Some species exist in equilibrium with their host, neither stimulating nor submitting to immune defenses mounted against them. Most are either opportunistic or true pathogens responsible for diseases such as pharyngitis, tooth decay, necrotizing fasciitis, infective endocarditis, and meningitis. Part of the success of streptococci as colonizers is attributable to the spectrum of proteins expressed on their surfaces. Adhesins enable interactions with salivary, serum, and extracellular matrix components; host cells; and other microbes. This is the essential first step to colonization, the development of complex communities, and possible invasion of host tissues. The majority of streptococcal adhesins are anchored to the cell wall via a C-terminal LPxTz motif. Other proteins may be surface anchored through N-terminal lipid modifications, while the mechanism of cell wall associations for others remains unclear. Collectively, these surface-bound proteins provide Streptococcus species with a "coat of many colors," enabling multiple intimate contacts and interplays between the bacterial cell and the host. In vitro and in vivo studies have demonstrated direct roles for many streptococcal adhesins as colonization or virulence factors, making them attractive targets for therapeutic and preventive strategies against streptococcal infections. There is, therefore, much focus on applying increasingly advanced molecular techniques to determine the precise structures and functions of these proteins, and their regulatory pathways, so that more targeted approaches can be developed.

Binding of the Streptococcus gordonii DL1 surface protein Hsa to the host cell membrane glycoproteins CD11b, CD43, and CD50

Infective endocarditis is frequently attributed to oral streptococci. The mechanisms of pathogenesis, however, are not well understood, although interaction between streptococci and phagocytes are thought to be very important. A highly expressed surface component of Streptococcus gordonii, Hsa, which has sialic acid-binding activity, contributes to infective endocarditis in vivo. In the present study, we found that S. gordonii DL1 binds to HL-60 cells differentiated into monocytes, granulocytes, and macrophages. Using a glutathione S-transferase (GST) fusion to the NR2 domain, which is the sialic acid-binding region of Hsa, we confirmed that the Hsa NR2 domain also binds to differentiated HL-60 cells. To identify which sialoglycoproteins on the surface of differentiated HL-60 cells are receptors for Hsa, intrinsic membrane proteins were assessed by bacterial overlay and far-Western blotting. S. gordonii DL1 adhered to 100- to 150-kDa proteins, a reaction that was abolished by neuraminidase treatment. These sialoglycoproteins were identified as CD11b, CD43, and CD50 by GST pull-down assay and immunoprecipitation with each specific monoclonal antibody. These data suggest that S. gordonii DL1 Hsa specifically binds to three glycoproteins as receptors and that this interaction may be the initial bacterial binding step in infective endocarditis by oral streptococci.

Implication of an outer surface lipoprotein in adhesion of Bifidobacterium bifidum to Caco-2 cells

We found that the human intestinal isolate Bifidobacterium bifidum MIMBb75 strongly adhered to Caco-2 cells. Proteinase K and lithium chloride treatments showed that proteins play a key role in MIMBb75 adhesion to Caco-2 cells. By studying the cell wall-associated proteins, we identified a surface protein, which we labeled BopA. We purified the protein chromatographically and found that it functioned as an adhesion promoter on Caco-2 cells. In silico analysis of the gene coding for this protein and globomycin experiments showed that BopA is a cysteine-anchored lipoprotein expressed as a precursor polypeptide. A database search indicated that BopA appears to function biologically as an oligopeptide/tripeptide-solute-binding protein in the ABC transport system. We discovered a protein corresponding to BopA and its gene in eight other highly adherent B. bifidum strains. Finally, we found that B. bifidum MIMBb75 and BopA affected the production of interleukin-8 in Caco-2 epithelial cells. BopA is the first protein described to date to be directly involved in the adhesion of bifidobacteria to Caco-2 cells and to show immunomodulatory activity.

Contribution of sialic acid-binding adhesin to pathogenesis of experimental endocarditis caused by Streptococcus gordonii DL1

An insertional mutation in hsa, the gene encoding the sialic acid-binding adhesin of Streptococcus gordonii DL1, resulted in a significant reduction of the infection rate of the organism and an inflammatory reaction in the rat aortic valve with experimental endocarditis, suggesting that the adhesin contributes to the infectivity of the organism for heart valves.

Analysis of recombinant group B streptococcal protein ScaAB and evaluation of its immunogenicity

Group B streptococcal (GBS) gene encoding the putative lipoprotein and adherence factor ScaAB was cloned and expressed in E. coli. Recombinant ScaAB protein was isolated. Signal sequence of ScaAB was found to be cleaved in the E. coli host. ScaAB recombinant protein was immunogenic in mice and antibodies against this protein were discovered in mice sera after GBS infection. The perspectives of the use of ScaAB protein in GBS vaccine are discussed.

Inactivation of Streptococcus gordonii SspAB alters expression of multiple adhesin genes

SspA and SspB (antigen I/II family proteins) can bind Streptococcus gordonii to other oral bacteria and also to salivary agglutinin glycoprotein, a constituent of the salivary film or pellicle that coats the tooth. To learn if SspA and SspB are essential for adhesion and initial biofilm formation on teeth, S. gordonii DL1 was incubated with saliva-coated hydroxyapatite (sHA) for 2 h in Todd-Hewitt broth with 20% saliva to develop initial biofilms. Sessile cells attached to sHA, surrounding planktonic cells, and free-growing cells were recovered separately. Free-growing cells expressed more sspA-specific mRNA and sspB-specific mRNA than sessile cells. Free-growing cells expressed the same levels of sspA and sspB as planktonic cells. Surprisingly, an SspA(-) SspB(-) mutant strain showed 2.2-fold greater biofilm formation on sHA than wild-type S. gordonii DL1. To explain this observation, we tested the hypothesis that inactivation of sspA and sspB genes altered the expression of other adhesin genes during initial biofilm formation in vitro. When compared to wild-type cells, expression of scaA and abpB was significantly up-regulated in the SspA(-) SspB(-) strain in sessile, planktonic, and free-growing cells. Consistent with this finding, ScaA antigen was also overexpressed in planktonic and free-growing SspA(-) SspB(-) cells compared to the wild type. SspA/B adhesins, therefore, were strongly suggested to be involved in the regulation of multiple adhesin genes.

Investigating the role of secA2 in secretion and glycosylation of a fimbrial adhesin in Streptococcus parasanguis FW213

Adhesion of Streptococcus parasanguis FW213, a primary colonizer, to the tooth surface is mediated mainly by peritrichous long fimbriae. The fimbrial structural unit, Fap1, is indispensable for fimbriae biogenesis, adhesion to an in vitro tooth model and biofilm formation. Mature Fap1 is a glycoprotein with an apparent molecular mass of 200 kDa. Glycosylated Fap1 is not present in some mutants screened from a transposon mutant library. Localization of the transposition sites revealed a gene determined to be secA2, which is distinct from the canonical secA gene. In FW213, glycosylated Fap1 was present in all the subcellular fractions including the cytoplasm. In VT1574, a non-polar mutant of secA2 generated by in frame deletion, Fap1 was not secreted. Glycosylated Fap1 was present in the membrane and cytoplasm of the mutant, although in greatly reduced amounts. Fap1 secretion and abundance were restored when VT1574 was complemented by a plasmid-borne secA2. The secretion defect of the secA2 mutation appears to be limited to a small group of proteins such as Fap1 and FimA. These data suggested that Fap1 secretion rather than glycosylation was the major effect of the deletion of secA2; however, this deletion also had an impact on Fap1 abundance. Two more secA2 mutants with different regions deleted were tested for their ability to secrete Fap1. One mutant was completely unable to secrete Fap1 while the other was able to secrete, but in a decreased amount. These data suggest that the region deleted in the latter mutant (nucleotides 2032-2337) is dispensable for Fap1 secretion.

Identification of Porphyromonas gingivalis genes specifically expressed in human gingival epithelial cells by using differential display reverse transcription-PCR

Porphyromonas gingivalis, one of the causative agents of adult periodontitis, can invade and survive within host epithelial cells. The molecular mechanisms by which P. gingivalis induces uptake and adapts to an intracellular environment are not fully understood. In this study, we have investigated the genetic responses of P. gingivalis internalized within human gingival epithelial cells (GECs) in order to identify factors involved in invasion and survival. We compared the differential display of arbitrarily PCR-amplified gene transcripts in P. gingivalis recovered from GECs with the display of transcripts in P. gingivalis control cultures. Over 20 potential differentially expressed transcripts were identified. Among these, pepO, encoding an endopeptidase, and genes encoding an ATP-binding cassette (ABC) transporter and a cation-transporting ATPase were upregulated in GECs. To investigate the functionality of these gene products, mutants were generated by insertional inactivation. Compared to the parental strain, mutants of each gene showed a significant reduction in their invasion capabilities. In addition, GEC cytoskeletal responses to the mutants were distinct from those induced by the parent. In contrast, adhesion of the mutant strains to GECs was not affected by lack of expression of the gene products. These results suggest that PepO, a cation-transporting ATPase, and an ABC transporter are required for the intracellular lifestyle of P. gingivalis.

Immunoblot method to detect Streptococcus pneumoniae and identify multiple serotypes from nasopharyngeal secretions

Conventional culture techniques are limited in the ability to detect multiple Streptococcus pneumoniae serotypes in nasopharyngeal (NP) secretions. We developed an immunoblot (IB) method with monoclonal antibodies (MAbs) to detect S. pneumoniae and to identify serotypes. NP specimens stored in skim milk-tryptone-glucose-glycerol medium were assessed by the IB method and the reference culture method (RM). In the RM, four optochin-sensitive alpha-hemolytic colonies resembling pneumococci were typed by the Quellung reaction. In the IB method, a nitrocellulose membrane blot of surface growth was reacted with a pneumococcal surface adhesion (PsaA) MAb and visualized. Of 47 NP specimens, 32 (68%) were found to be positive and 13 (28%) were found to be negative for pneumococci by both methods; each method alone yielded one positive result. The sensitivity and specificity of the IB method for the detection of pneumococci were 97 and 93%, respectively. To identify serotypes, blots were tested with serotype-specific MAbs (4, 6A, 6B, 9V, 14, 18C, 19F, and 23F). To detect the remaining serotypes, positive serotype-specific replicate blots were compared visually to an original anti-PsaA-positive blot; four unidentified colonies were subcultured and serotyped by the Quellung reaction. Fifty-eight S. pneumoniae-positive NP specimens containing 69 pneumococcal strains (23 serotypes) were tested; 68 (98.6%) of the strains were detected by the IB method, and 66 (95.6%) were detected by the RM. For 11 specimens found to contain two serotypes, both methods detected both serotypes in 7 (63.6%), the IB method alone detected the two serotypes in 3 (27.3%), and the RM alone detected both serotypes in 1 (9%). The IB method identified multiple clones and minor populations of pneumococci in NP secretions. This method is useful for detecting specific serotypes and carriage of multiple serotypes in epidemiologic surveillance and carriage studies.

Involvement of Streptococcus gordonii beta-glucoside metabolism systems in adhesion, biofilm formation, and in vivo gene expression

Streptococcus gordonii genes involved in beta-glucoside metabolism are induced in vivo on infected heart valves during experimental endocarditis and in vitro during biofilm formation on saliva-coated hydroxyapatite (sHA). To determine the roles of beta-glucoside metabolism systems in biofilm formation, the loci of these induced genes were analyzed. To confirm the function of genes in each locus, strains were constructed with gene inactivation, deletion, and/or reporter gene fusions. Four novel systems responsible for beta-glucoside metabolism were identified, including three phosphoenolpyruvate-dependent phosphotransferase systems (PTS) and a binding protein-dependent sugar uptake system for metabolizing multiple sugars, including beta-glucosides. Utilization of arbutin and esculin, aryl-beta-glucosides, was defective in some mutants. Esculin and oligochitosaccharides induced genes in one of the three beta-glucoside metabolism PTS and in four other genetic loci. Mutation of genes in any of the four systems affected in vitro adhesion to sHA, biofilm formation on plastic surfaces, and/or growth rate in liquid medium. Therefore, genes associated with beta-glucoside metabolism may regulate S. gordonii in vitro adhesion, biofilm formation, growth, and in vivo colonization.

The sloABCR operon of Streptococcus mutans encodes an Mn and Fe transport system required for endocarditis virulence and its Mn-dependent repressor

Streptococcus mutans belongs to the viridans group of oral streptococci, which is the leading cause of endocarditis in humans. The LraI family of lipoproteins in viridans group streptococci and other bacteria have been shown to function as virulence factors, adhesins, or ABC-type metal transporters. We previously reported the identification of the S. mutans LraI operon, sloABCR, which encodes components of a putative metal uptake system composed of SloA, an ATP-binding protein, SloB, an integral membrane protein, and SloC, a solute-binding lipoprotein, as well as a metal-dependent regulator, SloR. We report here the functional analysis of this operon. By Western blotting, addition of Mn to the growth medium repressed SloC expression in a wild-type strain but not in a sloR mutant. Other metals tested had little effect. Cells were also tested for aerobic growth in media stripped of metals then reconstituted with Mg and either Mn or Fe. Fe at 10 micro M supported growth of the wild-type strain but not of a sloA or sloC mutant. Mn at 0.1 micro M supported growth of the wild-type strain and sloR mutant but not of sloA or sloC mutants. The combined results suggest that the SloABC proteins transport both metals, although the SloR protein represses this system only in response to Mn. These conclusions are supported by (55)Fe uptake studies with Mn as a competitor. Finally, a sloA mutant demonstrated loss of virulence in a rat model of endocarditis, suggesting that metal transport is required for endocarditis pathogenesis.

MtuA, a lipoprotein receptor antigen from Streptococcus uberis, is responsible for acquisition of manganese during growth in milk and is essential for infection of the lactating bovine mammary gland

A mutant strain of Streptococcus uberis (AJS001) that was unable to grow in bovine milk was isolated following random insertional mutagenesis. The level of growth in milk was restored to that of the parental strain (strain 0140J) following addition of MnSO(4) but not following addition of other metal ions. The mutant contained a single insertion within mtuA, a homologue of mtsA and psaA, which encode metal-binding proteins in Streptococcus pyogenes and Streptococcus pneumoniae, respectively. Strain AJS001 was unable to infect any of eight quarters on four dairy cows following intramammary challenge with 10(5) CFU. Bacteria were never recovered directly from milk of these animals but were detected following enrichment in Todd-Hewitt broth in three of eight milk samples obtained within 24 h of challenge. The animals showed no inflammatory response and no signs of mastitis. Three mammary quarters on two different animals simultaneously challenged with 600 CFU of the parental strain, strain 0140J, became colonized, shed high numbers of S. uberis organisms in milk, displayed a marked inflammatory response to infection, and showed overt signs of mastitis. These data indicate that mtuA was required for efficient uptake of Mn(2+) during growth in bovine milk and infection of the lactating bovine mammary gland.

Growth, development, and gene expression in a persistent Streptococcus gordonii biofilm

A model for the protracted (30-day) colonization of smooth surfaces by Streptococcus gordonii that incorporates the nutrient flux that occurs in the oral cavity was developed. This model was used to characterize the biphasic expansion of the adherent bacterial population, which corresponded with the emergence of higher-order architectures characteristic of biofilms. Biofilm formation by S. gordonii was observed to be influenced by the presence of simple sugars including sucrose, glucose, and fructose. Real-time PCR was used to quantify changes in expression of S. gordonii genes known or thought to be involved in biofilm formation. Morphological changes were accompanied by a significant shift in gene expression patterns. The majority of S. gordonii genes examined were observed to be downregulated in the biofilm phase. Genes found to be upregulated in the biofilm state were observed to encode products related to environmental sensing and signaling.

Transition from reversible to irreversible attachment during biofilm formation by Pseudomonas fluorescens WCS365 requires an ABC transporter and a large secreted protein

We report the identification of an ATP-binding cassette (ABC) transporter and an associated large cell-surface protein that are required for biofilm formation by Pseudomonas fluorescens WCS365. The genes coding for these proteins are designated lap for large adhesion protein. The LapA protein, with a predicted molecular weight of approximately 900 kDa, is found to be loosely associated with the cell surface and present in the culture supernatant. The LapB, LapC and LapE proteins are predicted to be the cytoplasmic membrane-localized ATPase, membrane fusion protein and outer membrane protein component, respectively, of an ABC transporter. Consistent with this prediction, LapE, like other members of this family, is localized to the outer membrane. We propose that the lapEBC-encoded ABC transporter participates in the secretion of LapA, as strains with mutations in the lapEBC genes do not have detectable LapA associated with the cell surface or in the supernatant. The lap genes are conserved among environmental pseudomonads such as P. putida KT2440, P. fluorescens PfO1 and P. fluorescens WCS365, but are absent from pathogenic pseudomonads such as P. aeruginosa and P. syringae. The wild-type strain of P. fluorescens WCS365 and its lap mutant derivatives were assessed for their biofilm forming ability in static and flow systems. The lap mutant strains are impaired in an early step in biofilm formation and are unable to develop the mature biofilm structure seen for the wild-type bacterium. Time-lapse microscopy studies determined that the lap mutants are unable to progress from reversible (or transient) attachment to the irreversible attachment stage of biofilm development. The lap mutants were also found to be defective in attachment to quartz sand, an abiotic surface these organisms likely encounter in the environment.

Manganese: elemental defence for a life with oxygen

The presence of enzymes such as catalase, peroxidase and superoxide dismutase (SOD) obviates the problems associated with life in an aerobic environment by eliminating the harmful reactive oxygen species (ROS) that arise from respiration. Enzymic detoxification of ROS might not, however, be the only mechanism at work in bacteria. The accumulation of manganese (Mn), an abundant element in many environments, via several, recently identified transporters is thought to form the basis for an alternative, catalytic detoxification of ROS. An increasing body of evidence from work on the genetics and biochemistry of Mn accumulation and its cellular roles reveals that this overlooked defence mechanism is likely to be widespread among bacteria and might also contribute to virulence.

The divergently transcribed Streptococcus parasanguis virulence-associated fimA operon encoding an Mn(2+)-responsive metal transporter and pepO encoding a zinc metallopeptidase are not coordinately regulated

The study of how bacteria respond to and obtain divalent metal ions provides insight into the regulation of virulence factors in the host environment. Regulation of metal permease operons in gram-positive bacteria may involve the binding of metal-responsive repressors to palindromic domains in their control regions. The Streptococcus parasanguis fimA operon, which encodes an ATP-binding cassette (ABC) transporter system with sequence homology to the LraI family of metal transporters, possesses a palindromic regulatory region with high homology to that of the Streptococcus gordonii ScaR binding domain. Mapping of the promoter and regulatory regions of fimA and the divergently transcribed pepO gene, which encodes a zinc metalloendopeptidase, indicated that their promoter and regulatory elements overlap. fimA had one transcriptional start site, whereas pepO had three. Analysis of truncated versions of the pepO promoter suggested that all three transcriptional start sites are functional. Analysis of promoter activity under various environmental conditions indicated that the fimA operon promoter and the pepO promoter are not coordinately regulated. The fimA operon is responsive to changes in Mn(2+) concentration, but the pepO promoter is not. A S. parasanguis fimA mutant showed a growth deficiency under conditions of limiting Mn(2+). This deficiency was not alleviated by compensation with either Mg(2+) or Fe(3+). Wild-type S. parasanguis could take up Mn(2+) and Fe(3+), while the fimA mutant showed a marked reduction in this ability. These data suggested that FimA is a component of a metal transporter system capable of transporting both Mn(2+) and Fe(3+). FimA expression itself was shown to be responsive to Mn(2+) concentration, but not to availability of Fe(3+) or Mg(2+).

Oxidative stress tolerance is manganese (Mn(2+)) regulated in Streptococcus gordonii

The Sca permease in the oral bacterium Streptococcus gordonii is a member of a family of ATP-binding cassette (ABC)-type transporters for manganese (Mn(2+)) and related cations that are associated with streptococcal virulence in a number of infection models. Since Mn(2+) has a protective function against oxidative damage in a variety of bacteria, we have investigated the role of Sca permease in oxidative stress tolerance in Streptococcus gordonii. A single Mn(2+)-dependent superoxide dismutase (SOD), encoded by sodA, is expressed by S. gordonii and was >10-fold up-regulated under oxidative stress conditions. Inactivation of sodA resulted in increased susceptibility of S. gordonii cells to growth inhibition by dioxygen (O(2)), and to killing by paraquat (a superoxide anion generator) and by hydrogen peroxide (H(2)O(2)). Expression of thiol peroxidase, encoded by the tpx gene located immediately downstream of the scaCBA operon, was also up-regulated under oxidative conditions. Inactivation of tpx led to increased susceptibility of cells to H(2)O(2), but not to O(2) or paraquat. In low-Mn(2+) medium (0.01 micro M Mn(2+)) sodA and tpx genes were transcriptionally down-regulated, SOD activity was reduced and cells were more sensitive to growth inhibition by O(2). A Sca permease-deficient (scaC) mutant showed further reduced SOD activity and hypersensitivity to O(2) in medium containing <0.1 micro M Mn(2+). These results demonstrate that the Sca (Mn(2+)) permease in S. gordonii is essential for protection against oxidative stress.

Involvement of Lsp, a member of the LraI-lipoprotein family in Streptococcus pyogenes, in eukaryotic cell adhesion and internalization

Three open reading frames (ORFs) were identified by a genome walking strategy in the genomes of serotype M49 group A streptococcal (GAS) strains CS101 and 591. These ORFs were located between the mga core regulon and the dipeptide permease operon. The deduced amino acid (aa) sequences contained signature sequences indicative of a lipoprotein (306 aa), an intracellular protein (823 aa), and a secreted peptide (66 aa), respectively. ORF1 (named Lsp for lipoprotein of Streptococcus pyogenes) and ORF2 exhibited a high degree of homology to the lmb/ORF2 genes of S. agalactiae (B. Spellerberg et al., Infect. Immun. 67:871-878, 1999). The three ORFs were found to be present in each of the 27 GAS serotype strains tested. Transcription analysis revealed a polycistronic lsp/ORF2 and a monocistronic ORF3 message that were detected primarily at the transition from exponential to stationary growth phase. lsp and ORF2 mutants, ORF2- and ORF3-luciferase reporter fusions, and antiserum against recombinant Lsp were produced to examine the biological role of these genes. Although high Zn(2+) and Cu(2+) ion concentrations decreased lsp operon expression, Lsp did not transport divalent cations as described for other LraI-type operons. The lsp mutant had reduced fibronectin binding. Although no direct binding of Lsp to fibronectin could be demonstrated, the lsp mutant showed decreased transcription of prtF2 encoding the fibronectin-binding protein F2. Both the lsp and ORF2 mutants showed decreased laminin binding. Adherence to and internalization into A549 epithelial cells of both mutants was reduced without a detectable effect on eukaryotic cell viability. The transcription of a number of virulence factors was altered in the lsp mutants and ORF2 mutants. The changes in laminin binding and eukaryotic cell internalization could be explained by changes in transcription of speB (cysteine protease) and/or the global regulators mga, csrRS, and nra.

An accessory sec locus of Streptococcus gordonii is required for export of the surface protein GspB and for normal levels of binding to human platelets

The translocation of proteins across the bacterial cell membrane is carried out by highly conserved components of the Sec system. Most bacterial species have a single copy of the genes encoding SecA and SecY, which are essential for viability. However, Streptococcus gordonii strain M99 encodes SecA and SecY homologues that are not required for viability or for the translocation of most exported proteins. The genes (secA2 and secY2) reside in a region of the chromosome required for the export of GspB, a 286 kDa cell wall-anchored protein. Loss of GspB surface expression is associated with a significant reduction in the binding of M99 to human platelets, suggesting that it may be an adhesin. Genetic analyses indicate that M99 has a second, canonical SecA homologue that is essential for viability. At least two other Gram-positive species, Streptococcus pneumoniae and Staphylococcus aureus, encode two sets of SecA and SecY homologues. One set is more similar to SecA and SecY of Escherichia coli, whereas the other set is more similar to SecA2 and SecY2 of strain M99. The conserved organization of genes in the secY2-secA2 loci suggests that, in each of these Gram-positive species, SecA2 and SecY2 may constitute a specialized system for the transport of a very large serine-rich repeat protein.

A genome sequence survey of the mollicute corn stunt spiroplasma Spiroplasma kunkelii

The mollicute corn stunt spiroplasma (Spiroplasma kunkelii) is a leafhopper-transmitted pathogen of maize. Sequencing of the approximately 1.6-Mb genome of S. kunkelii was initiated to aid understanding the genetic basis of spiroplasma interactions with their plant and leafhopper hosts. In total, 144712 nucleotides of non-redundant, high-quality S. kunkelii genome sequence were obtained. Sequence tags were searched against the Mycoplasmataceae and Bacillus/Clostridium databases. Results showed that, in addition to spiroplasma phage SpV1 DNA insertions, spiroplasma genomes harbor more purine and amino acid biosynthesis, transcription regulation, cell envelope and DNA transport/binding genes than Mycoplasmataceae genomes. This investigation demonstrates that survey sequencing is an efficient procedure for gene discovery and genome characterization. The results of the S. kunkelii sequencing project are available at the Spiroplasma WebPage at http://www.oardc.ohio-state.edu/spiroplasma/genome.htm.

Virulence of Streptococcus pneumoniae: PsaA mutants are hypersensitive to oxidative stress

psaA encodes a 37-kDa pneumococcal lipoprotein which is part of an ABC Mn(II) transport complex. Streptococcus pneumoniae D39 psaA mutants have previously been shown to be significantly less virulent than wild-type D39, but the mechanism underlying the attenuation has not been resolved. In this study, we have shown that psaA and psaD mutants are highly sensitive to oxidative stress, i.e., to superoxide and hydrogen peroxide, which might explain why they are less virulent than the wild-type strain. Our investigations revealed altered expression of the key oxidative-stress response enzymes superoxide dismutase and NADH oxidase in psaA and psaD mutants, suggesting that PsaA and PsaD may play important roles in the regulation of expression of oxidative-stress response enzymes and intracellular redox homeostasis.

Identification of the psaA gene, coding for pneumococcal surface adhesin A, in viridans group streptococci other than Streptococcus pneumoniae

The gene encoding the pneumococcal surface adhesin A (PsaA) protein has been identified in three different viridans group streptococcal species. Comparative studies of the psaA gene identified in different pneumococcal isolates by sequencing PCR products showed a high degree of conservation among these strains. PsaA is encoded by an open reading frame of 930 bp. The analysis of this fragment in Streptococcus mitis, Streptococcus oralis, and Streptococcus anginosus strains revealed a sequence identity of 95, 94, and 90%, respectively, to the corresponding open reading frame of the previously reported Streptococcus pneumoniae serotype 6B strain. Our results confirm that psaA is present and detectable in heterologous bacterial species. The possible implications of these results for the suitability and potential use of PsaA in the identification and diagnosis of pneumococcal diseases are discussed.

Expression of Streptococcus mutans fimA is iron-responsive and regulated by a DtxR homologue

Iron uptake, transport and storage in Streptococcus mutans, the principal causative agent of human dental cavities, is unexplored despite early reports in the literature which predict a role for this trace metal in cariogenesis. Experiments in the authors' laboratory revealed several iron-responsive proteins in S. mutans, one of which reacted with a polyclonal antiserum directed against the FimA fimbrial adhesin from Streptococcus parasanguis on Western blots. The results of Western blot and Northern hybridization experiments support an inverse relationship between iron availability and S. mutans fimA expression, and metal ion uptake experiments implicate FimA in S. mutans (55)Fe transport. Cloning of the S. mutans fimA homologue facilitated the construction of a fimA knockout mutant which grew poorly in an iron-limiting medium relative to the wild-type progenitor strain, lending further support to a role for FimA in S. mutans iron transport. The authors also identified and cloned a dtxR-like gene (dlg) located downstream of fimA on the S. mutans chromosome, and noted increased fimA expression in a S. mutans dlg knockout mutant relative to wild-type on RNA spot blots and Western blots. The uptake of (55)Fe, which was also significantly increased in this mutant, was compromised in a fimA/dlg double knockout. These findings are consistent with a role for Dlg in the iron-mediated regulation of fimA, and possibly other S. mutans iron transporters. Finally, the cariogenic potential of the fimA and dlg knockout mutants was not significantly different from that of the wild-type progenitor in a germ-free rat model.

A new family of high-affinity ABC manganese and zinc permeases

Phylogenetic analysis of 47 extracellular putative metal binding receptors (MBRs) belonging to the newly defined cluster suggests the existence of two subclusters. The question of substrate specificity of the corresponding ATP binding cassette (ABC) permeases is discussed, based on data collected from 19 of them concerning their regulation, metal requirement of permease mutants, metal uptake and metal binding. The proposal that the two subclusters correspond to paralogous metal permeases dedicated primarily to manganese and to zinc transport is made. The question of a direct role of MBRs as adhesins of Gram-positive bacteria is then discussed and the importance of metal permeases for cellular processes and host-bacteria interactions is reviewed.

Oral microbial communities: biofilms, interactions, and genetic systems

Oral microbial-plaque communities are biofilms composed of numerous genetically distinct types of bacteria that live in close juxtaposition on host surfaces. These bacteria communicate through physical interactions called coaggregation and coadhesion, as well as other physiological and metabolic interactions. Streptococci and actinomyces are the major initial colonizers of the tooth surface, and the interactions between them and their substrata help establish the early biofilm community. Fusobacteria play a central role as physical bridges that mediate coaggregation of cells and as physiological bridges that promote anaerobic microenvironments which protect coaggregating strict anaerobes in an aerobic atmosphere. New technologies for investigating bacterial populations with 16S rDNA probes have uncovered previously uncultured bacteria and have offered an approach to in situ examination of the spatial arrangement of the participant cells in oral-plaque biofilms. Flow cells with saliva-coated surfaces are particularly useful for studies of biofilm formation and observation. The predicted sequential nature of colonization of the tooth surface by members of different genera can be investigated by using these new technologies and imaging the cells in situ with confocal scanning laser microscopy. Members of at least seven genera now can be subjected to genetic studies owing to the discovery of gene-transfer systems in these genera. Identification of contact-inducible genes in streptococci offers an avenue to explore bacterial responses to their environment and leads the way toward understanding communication among inhabitants of a multispecies biofilm.

Identification of lipoprotein homologues of pneumococcal PsaA in the equine pathogens Streptococcus equi and Streptococcus zooepidemicus

Streptococcus equi and Streptococcus zooepidemicus are major etiological agents of upper and lower airway disease in horses. Despite the considerable animal suffering and economic burden associated with these diseases, the factors that contribute to the virulence of these equine pathogens have not been extensively investigated. Here we demonstrate the presence of a homologue of the Streptococcus pneumoniae PsaA protein in both of these equine pathogens. Inhibition of signal peptide processing by the antibiotic globomycin confirmed the lipoprotein nature of the mature proteins, and surface exposure was confirmed by their release from intact cells by mild trypsinolysis.

Genetic characterization of a Streptococcus mutans LraI family operon and role in virulence

Proteins belonging to the LraI (for "lipoprotein receptor antigen") family function as adhesins in several streptococci, as a virulence factor for endocarditis in at least one of these species, and potentially as metal transporters in many bacteria. We have identified and characterized the chromosomal locus containing the LraI family gene (designated sloC) from Streptococcus mutans, an agent of dental caries and endocarditis in humans. Northern blot analysis indicated that sloC is cotranscribed with three other genes. As with other LraI operons, the sloA and sloB genes apparently encode components of an ATP-binding cassette transport system. The product of the fourth gene, sloR, has homology to the metal-dependent regulator from Corynebacterium diphtheriae, DtxR. A potential binding site for SloR was identified upstream from the sloABCR operon and was conserved upstream from LraI operons in several other streptococci. Potential SloR homologs were identified in the unfinished genomic sequences from two of these, S. pneumoniae and S. pyogenes. Mutagenesis of sloC in S. mutans resulted in apparent loss of expression of the entire operon as assessed by Northern blot analysis. The sloC mutant was indistinguishable from its wild-type parent in a gnotobiotic rat model of caries but was significantly less virulent in a rat model of endocarditis. Virulence for endocarditis was restored by correction of the sloC mutation but not by provision of the sloC gene in trans, suggesting that virulence requires the expression of other genes in the sloC operon.

Molecular analysis of putative pneumococcal virulence proteins

Although the polysaccharide capsule has been recognized as a sine qua non of virulence, recent attention has focused on the role of pneumococcal proteins in pathogenesis, particularly in view of their potential as vaccine antigens. The contribution of pneumolysin, two distinct neuraminidases, autolysin, hyaluronidase, and the 37 kDa pneumococcal surface adhesin A has been examined by specifically mutagenizing the respective genes in the pneumococcal chromosome and examining the impact on virulence in animal models. The vaccine potential of these proteins has also been assessed by immunization of mice with purified antigens, followed by challenge with virulent pneumococci.

Identification and characterization of a Streptococcus pyogenes ABC transporter with multiple specificity for metal cations

Metal ions are crucial trace elements for bacteria infecting the human host. The LraI (lipoprotein receptor-associated antigen I) transporter in Streptococcus spp. belongs to the superfamily of ABC transporters. The transporter consists of a lipoprotein, an ATP-binding protein and a hydrophobic integral membrane protein. Here, we describe a new member of the LraI family in the important human pathogen Streptococcus pyogenes. The system was identified in silico by analysis of the S. pyogenes Genome Sequencing Project. The S. pyogenes operon exhibits an atypical organization compared with equivalents in other Streptococcus spp. The presence and atypical organization of the operon was verified in a number of S. pyogenes strains of different serotypes. Transcriptional analysis of the LraI operon demonstrates a polycistronic transcription attenuated by a stable stem-loop structure, which allows the lipoprotein to be expressed in larger quantities than the other two components. The localization of the native lipoprotein at the bacterial surface was shown by proteolytic digestion of S. pyogenes bacteria and NH2-terminal sequencing of a released lipoprotein fragment. Recombinant lipoprotein was expressed as a GST fusion protein, and studies of molecular interactions with metal radioisotopes demonstrated that the protein has affinity for Zn(II), Fe(III) and Cu(II). Zn(II) and Cu(II) were found to compete for the same binding site, whereas Fe(III) uses a second site. Also, proton-induced X-ray analysis of lipoprotein samples identified iron, copper and zinc. Finally, a mutant strain lacking a functional mtsABC operon was generated and showed reduced uptake of 55Fe and 65Zn compared with the wild-type strain. The operon encoding this novel ABC transporter with multiple specificity for metal cations is designated mtsABC, for metal transporter of Streptococcus.

Streptococcus parasanguis pepO encodes an endopeptidase with structure and activity similar to those of enzymes that modulate peptide receptor signaling in eukaryotic cells

Studies in our laboratory have identified two fimbria-associated adhesins, FimA and Fap1, of Streptococcus parasanguis FW213. In this study, we isolated and sequenced DNA fragments linked to fimA to determine if they contained additional factors associated with adherence, virulence, or survival in the host. An open reading frame just upstream and divergently transcribed from the fimA operon was identified and named pepO. Northern hybridization indicated that pepO is transcribed as a monocistronic message. pepO encodes a predicted 631-amino-acid protein with a molecular mass of approximately 70.6 kDa. PepO contains the essential motif HEXXH, typical of many zinc-dependent metalloproteases and metallopeptidases. PepO has significant sequence identity to mammalian metallopeptidases, including endothelin-converting enzyme, which converts a potent vasoconstrictor into its active form, and neutral endopeptidase (NEP), which is involved in terminating the activity of opioid peptides. The opioid peptide metenkephalin is a natural substrate of NEP. Cell extracts of FW213 cleaved metenkephalin at the same site as does NEP, while an extract from an insertionally inactivated pepO mutant did not. These results indicate that FW213 pepO encodes an enzyme with activity similar to that of known mammalian endopeptidases. Phylogenetic analysis of PepO and its homologues suggests lateral genetic exchange between bacteria and eukaryotes.

Identification of oral mitis group streptococci by arbitrarily primed polymerase chain reaction

"Mitis group" streptococci are commensal but may play some role in dental caries, septicemia or endocarditis. Rapid genotypic identification would aid studies of dental plaque ecology, or diagnostic use. AP-PCR with 58 unpaired arbitrary primers was used to characterize 7 Streptococcus gordonii, 11 Streptococcus sanguis, 2 Streptococcus crista, 5 Streptococcus parasanguis, 18 Streptococcus oralis, and 36 Streptococcus mitis (22 biovar 1 and 14 biovar 2). S. parasanguis 16S rRNA variable region primer RR2 produced species-specific bands with all S. gordonii and S. sanguis. Human V beta 1 T-cell receptor primer 434 yielded concordant genotypic identification of all phenotypically defined S. crista and S. parasanguis, 83% of S. oralis, and 74% of S. mitis biovar 1. Amplicon patterns for S. mitis biovar 2 were heterogeneous. Findings suggest that primers RR2 and 434 in succession will allow rapid identification of genotypic groups corresponding closely to mitis group species established by phenotype.

Lmb, a protein with similarities to the LraI adhesin family, mediates attachment of Streptococcus agalactiae to human laminin

Streptococcus agalactiae is a leading cause of neonatal sepsis and meningitis. Adherence to extracellular matrix proteins is considered an important factor in the pathogenesis of infection, but the genetic determinants of this process remain largely unknown. We identified and sequenced a gene which codes for a putative lipoprotein that exhibits significant homology to the streptococcal LraI protein family. Mutants of this locus were demonstrated to have substantially reduced adherence to immobilized human laminin. The nucleotide sequence of the gene was subsequently designated lmb (laminin binding) and shown to be present in all of the common serotypes of S. agalactiae. To determine the role of Lmb in the adhesion of S. agalactiae wild-type strains to laminin, a recombinant Lmb protein harboring six consecutive histidine residues at the C terminus was cloned, expressed, and purified from Escherichia coli. Preincubation of immobilized laminin with recombinant Lmb significantly reduced adherence of the wild-type strain O90R to laminin. These results indicate that Lmb mediates the attachment of S. agalactiae to human laminin, which may be essential for the bacterial colonization of damaged epithelium and translocation of bacteria into the bloodstream.

The crystal structure of pneumococcal surface antigen PsaA reveals a metal-binding site and a novel structure for a putative ABC-type binding protein

BACKGROUND

. The surface protein PsaA of the pathogenic bacterium Streptococcus pneumoniae plays an essential role in its virulence. PsaA is a putative ATP-binding cassette-type (ABC-type) binding protein involved in the uptake of Mn2+ and possibly Zn2+ and is considered to be both a potential drug target and and a candidate vaccine component.

RESULTS

. The structure of PsaA has been determined to 2.0 A resolution using X-ray crystallography and is the first structure obtained for an ABC-type binding protein from a Gram-positive organism. The protein consists of two (beta/alpha)4 domains linked together by a single helix. A metal-binding site is formed in the domain interface by the sidechains of His67, His139, Glu205 and Asp280 and is occupied in the structure.

CONCLUSIONS

. The structural topology of PsaA is fundamentally different from that of other ABC-type binding proteins determined thus far in that PsaA lacks the characteristic 'hinge peptides' involved in conformational change upon solute uptake and release. In our structure, the metal-binding site is probably occupied by Zn2+. The site seems to be well conserved amongst related receptors from both Gram-positive and Gram-negative bacteria.

A streptococcal adhesion system for salivary pellicle and platelets

A Streptococcus sanguis 133-79 adhesin identified by the monoclonal antibody 1.1 (MAb 1.1) binds both saliva-coated hydroxylapatite (sHA) and platelets. The complementary binding site(s) for the adhesin was identified by the anti-idiotypical MAb 2.1. To learn if this adhesion system, marked by the antiadhesin MAb 1.1 and anti-binding site MAb 2.1, is commonly used by strains within the sanguis group and other viridans group streptococci, 42 strains from seven species were tested. Strains that bind to both sHA and platelets use the same adhesin and binding site epitopes. Strains that do not adhere to platelets rely on other adhesin specificities to bind to sHA.

Penicillin tolerance genes of Streptococcus pneumoniae: the ABC-type manganese permease complex Psa

Downregulation of the major autolysin in Streptococcus pneumoniae leads to penicillin tolerance, a feature that is characterized by the ability to survive but not grow in the presence of antibiotic. Screening a library of mutants in pneumococcal surface proteins for the ability to survive 10x minimum inhibitory concentration (MIC) of penicillin revealed over 10 candidate tolerance genes. One such mutant contained an insertion in the known gene psaA, which is part of the psa locus. This locus encodes an ABC-type Mn permease complex. Sequence analysis of adjacent DNA extended the known genetic organization of the locus to include two new open reading frames (ORFs), psaB, which encodes an ATP-binding protein, and psaC, which encodes a hydrophobic transmembrane protein. Mutagenesis of psaB, psaC, psaA and downstream psaD resulted in penicillin tolerance. Defective adhesion and reduced transformation efficiency, as reported previously for a psaA- mutant, were phenotypes shared by psaB-, psaC- and psaD- knockout mutants. Western blot analysis demonstrated that the set of mutants expressed RecA, but none of them showed translation of the autolysin gene, which is located downstream of recA. The addition of manganese (Mn) failed to correct the abnormal physiology. These results suggest that this ABC-type Mn permease complex has a pleiotropic effect on pneumococcal physiology including adherence and autolysis. These are the first genes suggested as being involved in triggering autolysin. The results raise the possibility that loss of function of PsaA, by vaccine-induced antibody for instance, may promote penicillin tolerance.