Streptococcal collagen-like surface protein 1 promotes adhesion to the respiratory epithelial cell

Comparative Genomic and Metagenomic Investigations of the Corynebacterium tuberculostearicum Species Complex Reveals Potential Mechanisms Underlying Associations To Skin Health and Disease

Corynebacterium are a diverse genus and dominant member of the human skin microbiome. Recently, we reported that the most prevalent Corynebacterium species found on skin, including Corynebacterium tuberculostearicum and Corynebacterium kefirresidentii, comprise a narrow species complex despite the diversity of the genus. Here, we apply high-resolution phylogenomics and comparative genomics to describe the structure of the C. tuberculostearicum species complex and highlight genetic traits which are enriched or depleted in it relative to other Corynebacterium. Through metagenomic investigations, we also find that individual species within the complex can associate with specific body sites. Finally, we discover that one species from the complex, C. kefirresidentii, increases in relative abundance during atopic dermatitis flares, and show that most genomes of this species encode a colocalized set of putative virulence genes. IMPORTANCE Corynebacterium are commonly found bacteria on the human skin. In this study, we perform comparative genomics to gain insight into genetic traits which differentiate a phylogenetically related group of Corynebacterium, the Corynebacterium tuberculostearicum species complex, that includes the most prevalent species from the genus in skin microbiomes. After resolving the presence of distinct species within the complex, we applied metagenomic analysis to uncover biogeographic associations of individual species within the complex with specific body sites and discovered that one species, commonly found in the nares of individuals, increases in abundance across multiple body sites during atopic dermatitis flares.

Lactiplantibacillus plantarum KAU007 Extract Modulates Critical Virulence Attributes and Biofilm Formation in Sinusitis Causing Streptococcus pyogenes

Streptococcus pyogenes is one of the most common bacteria causing sinusitis in children and adult patients. Probiotics are known to cause antagonistic effects on S. pyogenes growth and biofilm formation. In the present study, we demonstrated the anti-biofilm and anti-virulence properties of Lactiplantibacillus plantarum KAU007 against S. pyogenes ATCC 8668. The antibacterial potential of L. plantarum KAU007 metabolite extract (LME) purified from the cell-free supernatant of L. plantarum KAU007 was evaluated in terms of minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC). LME was further analyzed for its anti-biofilm potential using crystal violet assay and microscopic examination. Furthermore, the effect of LME was tested on the important virulence attributes of S. pyogenes, such as secreted protease production, hemolysis, extracellular polymeric substance production, and cell surface hydrophobicity. Additionally, the impact of LME on the expression of genes associated with biofilm formation and virulence attributes was analyzed using qPCR. The results revealed that LME significantly inhibited the growth and survival of S. pyogenes at a low concentration (MIC, 9.76 µg/mL; MBC, 39.06 µg/mL). Furthermore, LME inhibited biofilm formation and mitigated the production of extracellular polymeric substance at a concentration of 4.88 μg/mL in S. pyogenes. The results obtained from qPCR and biochemical assays advocated that LME suppresses the expression of various critical virulence-associated genes, which correspondingly affect various pathogenicity markers and were responsible for the impairment of virulence and biofilm formation in S. pyogenes. The non-hemolytic nature of LME and its anti-biofilm and anti-virulence properties against S. pyogenes invoke further investigation to study the role of LME as an antibacterial agent to combat streptococcal infections.

Towards understanding mechanisms and functional consequences of bacterial interactions with members of various kingdoms in complex biofilms that abound in nature

The microbial world represents a phenomenal diversity of microorganisms from different kingdoms of life which occupy an impressive set of ecological niches. Most, if not all, microorganisms once colonise a surface develop architecturally complex surface-adhered communities which we refer to as biofilms. They are embedded in polymeric structural scaffolds serve as a dynamic milieu for intercellular communication through physical and chemical signalling. Deciphering microbial ecology of biofilms in various natural or engineered settings has revealed co-existence of microorganisms from all domains of life, including Bacteria, Archaea and Eukarya. The coexistence of these dynamic microbes is not arbitrary, as a highly coordinated architectural setup and physiological complexity show ecological interdependence and myriads of underlying interactions. In this review, we describe how species from different kingdoms interact in biofilms and discuss the functional consequences of such interactions. We highlight metabolic advances of collaboration among species from different kingdoms, and advocate that these interactions are of great importance and need to be addressed in future research. Since trans-kingdom biofilms impact diverse contexts, ranging from complicated infections to efficient growth of plants, future knowledge within this field will be beneficial for medical microbiology, biotechnology, and our general understanding of microbial life in nature.

Role for Cell-Surface Collagen of Streptococcus pyogenes in Infections

Group A Streptococcus (GAS) displays cell-surface proteins that resemble human collagen. We find that a fluorophore-labeled collagen mimetic peptide (CMP) labels GAS cells but not Escherichia coli or Bacillus subtilis cells, which lack such proteins. The CMP likely engages in a heterotrimeric helix with endogenous collagen, as the nonnatural d enantiomer of the CMP does not label GAS cells. To identify a molecular target, we used reverse genetics to "knock-in" the GAS genes that encode two proteins with collagen-like domains, Scl1 and Scl2, into B. subtilis. The fluorescent CMP labels the cells of these B. subtilis strains. Moreover, these strains bind tightly to a surface of mammalian collagen. These data are consistent with streptococcal collagen forming triple helices with damaged collagen in a wound bed and thus have implications for microbial virulence.

Fungal biofilm morphology impacts hypoxia fitness and disease progression

Microbial populations form intricate macroscopic colonies with diverse morphologies whose functions remain to be fully understood. Despite fungal colonies isolated from environmental and clinical samples revealing abundant intraspecies morphological diversity, it is unclear how this diversity affects fungal fitness and disease progression. Here we observe a notable effect of oxygen tension on the macroscopic and biofilm morphotypes of the human fungal pathogen Aspergillus fumigatus. A hypoxia-typic morphotype is generated through the expression of a subtelomeric gene cluster containing genes that alter the hyphal surface and perturb interhyphal interactions to disrupt in vivo biofilm and infection site morphologies. Consequently, this morphotype leads to increased host inflammation, rapid disease progression and mortality in a murine model of invasive aspergillosis. Taken together, these data suggest that filamentous fungal biofilm morphology affects fungal-host interactions and should be taken into consideration when assessing virulence and host disease progression of an isolated strain.

Mycobacterium tuberculosis Primary Infection and Dissemination: A Critical Role for Alveolar Epithelial Cells

Globally, tuberculosis (TB) has reemerged as a major cause of morbidity and mortality, despite the use of the Mycobacterium bovis BCG vaccine and intensive attempts to improve upon BCG or develop new vaccines. Two lacunae in our understanding of the Mycobacterium tuberculosis (M. tb)-host pathogenesis have mitigated the vaccine efforts; the bacterial-host interaction that enables successful establishment of primary infection and the correlates of protection against TB. The vast majority of vaccine efforts are based on the premise that cell-mediated immunity (CMI) is the predominating mode of protection against TB. However, studies in animal models and in humans demonstrate that post-infection, a period of several weeks precedes the initiation of CMI during which the few inhaled bacteria replicate dramatically and disseminate systemically. The “Trojan Horse” mechanism, wherein M. tb is phagocytosed and transported across the alveolar barrier by infected alveolar macrophages has been long postulated as the sole, primary M. tb:host interaction. In the current review, we present evidence from our studies of transcriptional profiles of M. tb in sputum as it emerges from infectious patients where the bacteria are in a quiescent state, to its adaptations in alveolar epithelial cells where the bacteria transform to a highly replicative and invasive phenotype, to its maintenance of the invasive phenotype in whole blood to the downregulation of invasiveness upon infection of epithelial cells at an extrapulmonary site. Evidence for this alternative mode of infection and dissemination during primary infection is supported by in vivo, in vitro cell-based, and transcriptional studies from multiple investigators in recent years. The proposed alternative mechanism of primary infection and dissemination across the alveolar barrier parallels our understanding of infection and dissemination of other Gram-positive pathogens across their relevant mucosal barriers in that barrier-specific adhesins, toxins, and enzymes synergize to facilitate systemic establishment of infection prior to the emergence of CMI. Further exploration of this M. tb:non-phagocytic cell interaction can provide alternative approaches to vaccine design to prevent infection with M. tb and not only decrease clinical disease but also decrease the overwhelming reservoir of latent TB infection.

Collagen degradation in tuberculosis pathogenesis: the biochemical consequences of hosting an undesired guest

The scenario of chemical reactions prompted by the infection by Mycobacterium tuberculosis is huge. The infection generates a localized inflammatory response, with the recruitment of neutrophils, monocytes, and T-lymphocytes. Consequences of this immune reaction can be the eradication or containment of the infection, but these events can be deleterious to the host inasmuch as lung tissue can be destroyed. Indeed, a hallmark of tuberculosis (TB) is the formation of lung cavities, which increase disease development and transmission, as they are sites of high mycobacterial burden. Pulmonary cavitation is associated with antibiotic failure and the emergence of antibiotic resistance. For cavities to form, M. tuberculosis induces the overexpression of host proteases, like matrix metalloproteinases and cathepsin, which are secreted from monocyte-derived cells, neutrophils, and stromal cells. These proteases destroy the lung parenchyma, in particular the collagen constituent of the extracellular matrix (ECM). Namely, in an attempt to destroy infected cells, the immune reactions prompted by mycobacterial infections induce the destruction of vital regions of the lung, in a process that can become fatal. Here, we review structure and function of the main molecular actors of ECM degradation due to M. tuberculosis infection and the proposed mechanisms of tissue destruction, mainly attacking fibrillar collagen. Importantly, enzymes responsible for collagen destruction are emerging as key targets for adjunctive therapies to limit immunopathology in TB.

Surface-exposed loops and an acidic patch in the Scl1 protein of group A Streptococcus enable Scl1 binding to wound-associated fibronectin

Keratinized epidermis constitutes a powerful barrier of the mucosa and skin, effectively preventing bacterial invasion, unless it is wounded and no longer protective. Wound healing involves deposition of distinct extracellular matrix (ECM) proteins enriched in cellular fibronectin (cFn) isoforms containing extra domain A (EDA). The streptococcal collagen-like protein 1 (Scl1) is a surface adhesin of group A Streptococcus (GAS), which contains an N-terminal variable (V) domain and a C-terminally located collagen-like domain. During wound infection, Scl1 selectively binds EDA/cFn isoforms and laminin, as well as low-density lipoprotein (LDL), through its V domain. The trimeric V domain has a six-helical bundle fold composed of three pairs of anti-parallel α-helices interconnected by hypervariable loops, but the roles of these structures in EDA/cFn binding are unclear. Here, using recombinant Scl (rScl) constructs to investigate structure-function determinants of the Scl1-EDA/cFn interaction, we found that full-length rScl1, containing both the globular V and the collagen domains, is necessary for EDA/cFn binding. We established that the surface-exposed loops, interconnecting conserved α-helices, guide recognition and binding of Scl1-V to EDA and binding to laminin and LDL. Moreover, electrostatic surface potential models of the Scl1-V domains pointed to a conserved, negatively charged pocket, surrounded by positively charged and neutral regions, as a determining factor for the binding. In light of these findings, we propose an updated model of EDA/cFn recognition by the Scl1 adhesin from GAS, representing a significant step in understanding the Scl1-ECM interactions within the wound microenvironment that underlie GAS pathogenesis.

Assessment of Cpa, Scl1 and Scl2 in clinical group A streptococcus isolates and patients from north India: an evaluation of the host pathogen interaction

Group A streptococcus (GAS) infection remains a major concern due to multiple diseases including pharyngitis, impetigo, acute rheumatic fever (ARF) and rheumatic heart disease (RHD). It uses different adhesins and virulence factors like Cpa (collagen binding protein) and Scl (collagen-like protein) in its pathogenicity. Scl having similarities with human collagen may contribute to inducing autoimmunity in the host. Here we assessed gene expression, antibody titer of Cpa, Scl1 and Scl2 in both clinical GAS isolates (n = 45) and blood (n = 45) obtained from pharyngitis, ARF (acute rheumatic fever) and RHD respectively. Skin isolates (n = 30) were obtained from impetigo patients. The study revealed a total of 27 GAS emm types. Frequency of cpa, scl1, scl2 was high in ARF isolates. The antibody titer of these proteins was high in all isolates, and also in patients with pharyngitis and ARF. All isolates showed high binding affinity toward collagen I and IV, which further indicates a potential host pathogen interaction. Our study reflects a strong association of Cpa and Scls in early and post-GAS pathogenicity. However, the increased antibody titer of Scl1 and Scl2 during ARF may be attributed to a cogent immune response in the host.

Streptococcus pyogenes adhesion and colonization

Streptococcus pyogenes (group A Streptococcus, GAS) is a human-adapted pathogen responsible for a wide spectrum of disease. GAS can cause relatively mild illnesses, such as strep throat or impetigo, and less frequent but severe life-threatening diseases such as necrotizing fasciitis and streptococcal toxic shock syndrome. GAS is an important public health problem causing significant morbidity and mortality worldwide. The main route of GAS transmission between humans is through close or direct physical contact, and particularly via respiratory droplets. The upper respiratory tract and skin are major reservoirs for GAS infections. The ability of GAS to establish an infection in the new host at these anatomical sites primarily results from two distinct physiological processes, namely bacterial adhesion and colonization. These fundamental aspects of pathogenesis rely upon a variety of GAS virulence factors, which are usually under strict transcriptional regulation. Considerable progress has been made in better understanding these initial infection steps. This review summarizes our current knowledge of the molecular mechanisms of GAS adhesion and colonization.

Knockout of the adp gene related with colonization in Bacillus nematocida B16 using customized transcription activator-like effectors nucleases

Bacillus nematocida B16 is able to dominate in the intestines of the worm Caenorhabditis elegans in 'Trojan horse' pathogenic mechanism. The adp is one candidate gene which potentially play a vital role in the colonization from our previous random mutagenesis screening results. To analyse the functional role of this gene, we constructed the adp knockout mutant through customized transcription activator-like effectors nucleases (TALEN), which has been successfully used in yeasts, nematodes, zebrafish and human pluripotent cells. Here, we first time report this knockout method in bacteria on this paper. Bioassay experiments demonstrated that the adp knockout mutant of B16 showed considerably lower colonization activity, reduced numbers of intestines and less than 80% nematocidal activity compared with the wild-type strain when infected for 48 h. However, no obvious change on proteolytic activity was observed in the mutant. Conversely, the complementation of adp gene restored most of the above deficient phenotypes. These results indicated that the adp gene was involved in surface adhesion and played a comparatively important role in colonizing host nematodes. Moreover, TALENs successfully disrupt target genes in bacteria.

Transcriptional profile of Mycobacterium tuberculosis replicating in type II alveolar epithelial cells

Mycobacterium tuberculosis (M. tb) infection is initiated by the few bacilli inhaled into the alveolus. Studies in lungs of aerosol-infected mice provided evidence for extensive replication of M. tb in non-migrating, non-antigen-presenting cells in the alveoli during the first 2-3 weeks post-infection. Alveoli are lined by type II and type I alveolar epithelial cells (AEC) which outnumber alveolar macrophages by several hundred-fold. M. tb DNA and viable M. tb have been demonstrated in AEC and other non-macrophage cells of the kidney, liver, and spleen in autopsied tissues from latently-infected subjects from TB-endemic regions indicating systemic bacterial dissemination during primary infection. M. tb have also been demonstrated to replicate rapidly in A549 cells (type II AEC line) and acquire increased invasiveness for endothelial cells. Together, these results suggest that AEC could provide an important niche for bacterial expansion and development of a phenotype that promotes dissemination during primary infection. In the current studies, we have compared the transcriptional profile of M. tb replicating intracellularly in A549 cells to that of M. tb replicating in laboratory broth, by microarray analysis. Genes significantly upregulated during intracellular residence were consistent with an active, replicative, metabolic, and aerobic state, as were genes for tryptophan synthesis and for increased virulence (ESAT-6, and ESAT-6-like genes, esxH, esxJ, esxK, esxP, and esxW). In contrast, significant downregulation of the DevR (DosR) regulon and several hypoxia-induced genes was observed. Stress response genes were either not differentially expressed or were downregulated with the exception of the heat shock response and those induced by low pH. The intra-type II AEC M. tb transcriptome strongly suggests that AEC could provide a safe haven in which M. tb can expand dramatically and disseminate from the lung prior to the elicitation of adaptive immune responses.

Symbiodinium transcriptome and global responses of cells to immediate changes in light intensity when grown under autotrophic or mixotrophic conditions

Symbiosis between unicellular dinoflagellates (genus Symbiodinium) and their cnidarian hosts (e.g. corals, sea anemones) is the foundation of coral reef ecosystems. Dysfunction of this symbiosis under changing environmental conditions has led to global reef decline. Little information is known about Symbiodinium gene expression and mechanisms by which light impacts host-symbiont associations. To address these issues, we generated a transcriptome from axenic Symbiodinium strain SSB01. Here we report features of the transcriptome, including occurrence and length distribution of spliced leader sequences, the functional landscape of encoded proteins and the impact of light on gene expression. Expression of many Symbiodinium genes appears to be significantly impacted by light. Transcript encoding cryptochrome 2 declined in high light while some transcripts for Regulators of Chromatin Condensation (RCC1) declined in the dark. We also identified a transcript encoding a light harvesting AcpPC protein with homology to Chlamydomonas LHCSR2. The level of this transcript increased in high light autotrophic conditions, suggesting that it is involved in photo-protection and the dissipation of excess absorbed light energy. The most extensive changes in transcript abundances occurred when the algae were transferred from low light to darkness. Interestingly, transcripts encoding several cell adhesion proteins rapidly declined following movement of cultures to the dark, which correlated with a dramatic change in cell surface morphology, likely reflecting the complexity of the extracellular matrix. Thus, light-sensitive cell adhesion proteins may play a role in establishing surface architecture, which may in turn alter interactions between the endosymbiont and its host.

Molecular and genomic characterization of pathogenic traits of group A Streptococcus pyogenes

Group A streptococcus (GAS) or Streptococcus pyogenes causes various diseases ranging from self-limiting sore throat to deadly invasive diseases. The genome size of GAS is 1.85-1.9 Mb, and genomic rearrangement has been demonstrated. GAS possesses various surface-associated substances such as hyaluronic capsule, M proteins, and fibronectin/laminin/immunoglobulin-binding proteins. These are related to the virulence and play multifaceted and mutually reflected roles in the pathogenesis of GAS infections. Invasion of GAS into epithelial cells and deeper tissues provokes immune and non-immune defense or inflammatory responses including the recruitment of neutrophils, macrophages, and dendritic cells in hosts. GAS frequently evades host defense mechanisms by using its virulence factors. Extracellular products of GAS may perturb cellular and subcellular functions and degrade tissues enzymatically, which leads to the aggravation of local and/or systemic disorders in the host. In this review, we summarize some important cellular and extracellular substances that may affect pathogenic processes during GAS infections, and the host responses to these.

Role for streptococcal collagen-like protein 1 in M1T1 group A Streptococcus resistance to neutrophil extracellular traps

Streptococcal collagen-like protein 1 (Scl-1) is one of the most highly expressed proteins in the invasive M1T1 serotype group A Streptococcus (GAS), a globally disseminated clone associated with higher risk of severe invasive infections. Previous studies using recombinant Scl-1 protein suggested a role in cell attachment and binding and inhibition of serum proteins. Here, we studied the contribution of Scl-1 to the virulence of the M1T1 clone in the physiological context of the live bacterium by generating an isogenic strain lacking the scl-1 gene. Upon subcutaneous infection in mice, wild-type bacteria induced larger lesions than the Δscl mutant. However, loss of Scl-1 did not alter bacterial adherence to or invasion of skin keratinocytes. We found instead that Scl-1 plays a critical role in GAS resistance to human and murine phagocytic cells, allowing the bacteria to persist at the site of infection. Phenotypic analyses demonstrated that Scl-1 mediates bacterial survival in neutrophil extracellular traps (NETs) and protects GAS from antimicrobial peptides found within the NETs. Additionally, Scl-1 interferes with myeloperoxidase (MPO) release, a prerequisite for NET production, thereby suppressing NET formation. We conclude that Scl-1 is a virulence determinant in the M1T1 GAS clone, allowing GAS to subvert innate immune functions that are critical in clearing bacterial infections.

Polyproline and triple helix motifs in host-pathogen recognition

Secondary structure elements often mediate protein-protein interactions. Despite their low abundance in folded proteins, polyproline II (PPII) and its variant, the triple helix, are frequently involved in protein-protein interactions, likely due to their peculiar propensity to be solvent-exposed. We here review the role of PPII and triple helix in mediating host-pathogen interactions, with a particular emphasis to the structural aspects of these processes. After a brief description of the basic structural features of these elements, examples of host-pathogen interactions involving these motifs are illustrated. Literature data suggest that the role played by PPII motif in these processes is twofold. Indeed, PPII regions may directly mediate interactions between proteins of the host and the pathogen. Alternatively, PPII may act as structural spacers needed for the correct positioning of the elements needed for adhesion and infectivity.

Recent investigations have highlighted that collagen triple helix is also a common target for bacterial adhesins. Although structural data on complexes between adhesins and collagen models are rather limited, experimental and theoretical studies have unveiled some interesting clues of the recognition process. Interestingly, very recent data show that not only is the triple helix used by pathogens as a target in the host-pathogen interaction but it may also act as a bait in these processes since bacterial proteins containing triple helix regions have been shown to interact with host proteins.

As both PPII and triple helix expose several main chain non-satisfied hydrogen bond acceptors and donors, both elements are highly solvated. The preservation of the solvation state of both PPII and triple helix upon protein-protein interaction is an emerging aspect that will be here thoroughly discussed.

Prediction of molecular mimicry candidates in human pathogenic bacteria

Molecular mimicry of host proteins is a common strategy adopted by bacterial pathogens to interfere with and exploit host processes. Despite the availability of pathogen genomes, few studies have attempted to predict virulence-associated mimicry relationships directly from genomic sequences. Here, we analyzed the proteomes of 62 pathogenic and 66 non-pathogenic bacterial species, and screened for the top pathogen-specific or pathogen-enriched sequence similarities to human proteins. The screen identified approximately 100 potential mimicry relationships including well-characterized examples among the top-scoring hits (e.g., RalF, internalin, yopH, and others), with about 1/3 of predicted relationships supported by existing literature. Examination of homology to virulence factors, statistically enriched functions, and comparison with literature indicated that the detected mimics target key host structures (e.g., extracellular matrix, ECM) and pathways (e.g., cell adhesion, lipid metabolism, and immune signaling). The top-scoring and most widespread mimicry pattern detected among pathogens consisted of elevated sequence similarities to ECM proteins including collagens and leucine-rich repeat proteins. Unexpectedly, analysis of the pathogen counterparts of these proteins revealed that they have evolved independently in different species of bacterial pathogens from separate repeat amplifications. Thus, our analysis provides evidence for two classes of mimics: complex proteins such as enzymes that have been acquired by eukaryote-to-pathogen horizontal transfer, and simpler repeat proteins that have independently evolved to mimic the host ECM. Ultimately, computational detection of pathogen-specific and pathogen-enriched similarities to host proteins provides insights into potentially novel mimicry-mediated virulence mechanisms of pathogenic bacteria.

AhrC and Eep are biofilm infection-associated virulence factors in Enterococcus faecalis

Enterococcus faecalis is part of the human intestinal microbiome and is a prominent cause of health care-associated infections. The pathogenesis of many E. faecalis infections, including endocarditis and catheter-associated urinary tract infection (CAUTI), is related to the ability of clinical isolates to form biofilms. To identify chromosomal genetic determinants responsible for E. faecalis biofilm-mediated infection, we used a rabbit model of endocarditis to test strains with transposon insertions or in-frame deletions in biofilm-associated loci: ahrC, argR, atlA, opuBC, pyrC, recN, and sepF. Only the ahrC mutant was significantly attenuated in endocarditis. We demonstrate that the transcriptional regulator AhrC and the protease Eep, which we showed previously to be an endocarditis virulence factor, are also required for full virulence in murine CAUTI. Therefore, AhrC and Eep can be classified as enterococcal biofilm-associated virulence factors. Loss of ahrC caused defects in early attachment and accumulation of biofilm biomass. Characterization of ahrC transcription revealed that the temporal expression of this locus observed in wild-type cells promotes initiation of early biofilm formation and the establishment of endocarditis. This is the first report of AhrC serving as a virulence factor in any bacterial species.

Collagen-like proteins in pathogenic E. coli strains

The genome sequences of enterohaemorrhagic E. coli O157:H7 strains show multiple open-reading frames with collagen-like sequences that are absent from the common laboratory strain K-12. These putative collagens are included in prophages embedded in O157:H7 genomes. These prophages carry numerous genes related to strain virulence and have been shown to be inducible and capable of disseminating virulence factors by horizontal gene transfer. We have cloned two collagen-like proteins from E. coli O157:H7 into a laboratory strain and analysed the structure and conformation of the recombinant proteins and several of their constituting domains by a variety of spectroscopic, biophysical, and electron microscopy techniques. We show that these molecules exhibit many of the characteristics of vertebrate collagens, including trimer formation and the presence of a collagen triple helical domain. They also contain a C-terminal trimerization domain, and a trimeric α-helical coiled-coil domain with an unusual amino acid sequence almost completely lacking leucine, valine or isoleucine residues. Intriguingly, these molecules show high thermal stability, with the collagen domain being more stable than those of vertebrate fibrillar collagens, which are much longer and post-translationally modified. Under the electron microscope, collagen-like proteins from E. coli O157:H7 show a dumbbell shape, with two globular domains joined by a hinged stalk. This morphology is consistent with their likely role as trimeric phage side-tail proteins that participate in the attachment of phage particles to E. coli target cells, either directly or through assembly with other phage tail proteins. Thus, collagen-like proteins in enterohaemorrhagic E. coli genomes may have a direct role in the dissemination of virulence-related genes through infection of harmless strains by induced bacteriophages.

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

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

Vaccine candidates PhtD and PhtE of Streptococcus pneumoniae are adhesins that elicit functional antibodies in humans

We evaluated the role of vaccine candidate surface proteins, PhtD and PhtE as antigens with functional importance for Streptococcus pneumoniae (pneumococci) in adherence to nasopharyngeal (D562) and lung (A549) epithelial cell lines. Comparing TIGR4 to PhtD and PhtE- isogenic mutants, a 40% (p=0.001) and 42% (p=0.002) drop in the number of epithelial cells with adherent pneumococci was observed to both cells lines with the mutants, as quantitated using flow cytometry. We expressed PhtD and PhtE on the surface of Escherichia coli and demonstrated that when PhtD and PhtE were surface expressed on E. coli, adherence increased to D562 and A549 cells, compared with the E. coli parent strain (p=0.005, 0.013 for D562 and p=0.034, p=0.035 for A549). Using flow cytometry and confocal microscopy we found that pneumococci aggregated in the presence of human serum IgG, leading to a non-specific drop in adherence. Therefore IgG Fab fragments were prepared to study the functional role of PhtD and PhtE-specific Fabs in blocking adherence. The addition of 1μg of IgG Fab from adult sera led to a 34% reduction (p=0.002) and from children a 20% (p=0.023) reduction in D562 epithelial cells with adherent pneumococci. In purified IgG from adult sera, the depletion of PhtD and PhtE specific Fab from total IgG Fab resulted in a significant increase in the number of D562 epithelial cells with adherent pneumococci (p=0.005 for PhtD and p=0.024 for PhtE). We conclude that antibody directed to PhtD and PhtE adhesins of pneumococci, if raised by vaccination, may function to prevent pneumococcal adherence to human airway epithelial cells.