OmpA-like protein influences cell shape and adhesive activity of Tannerella forsythia

Lactobacillus reuteri for chronic periodontitis: focus on underlying mechanisms and future perspectives

Chronic periodontitis is a common oral disorder caused by pathogenic bacteria. Despite the wide use of antibiotics as the conventional adjunctive treatment, the challenges of increased antibiotic resistance and limited therapeutic effect receive considerable attention and the developments of alternative treatments gain increasing consideration. Growing evidence showed that Lactobacillus reuteri (LR) may represent a promising alternative adjunct for chronic periodontitis. It can attenuate inflammation and reduce tissue disruption. LR-assisted treatment has been shown to be effective and relatively safe in multiple clinical trials, and accumulating evidence suggests its significant biological roles. In the current review, we focus on capturing the underlying mechanisms of LR involved in chronic periodontitis, thereby representing a scientific foundation for LR-assisted therapy. Furthermore, we point out the challenges and future directions for further clinical trials to improve the clinical applicability for LR.

Proteomic analysis reveals the non-coding small RNA Qrr5 influences autoaggregation and growth competition in Vibrio parahaemolyticus

Vibrio parahaemolyticus, a sea-born bacterial pathogen, is a primary inducement of food-borne gastroenteritis. Previous studies have shown that non-coding small RNA plays a vital role in the regulation of multiple biological processes in pathogenic bacteria, especially autoaggregation and growth competition. However, the inherent mechanisms have not yet to be fully understood. As important regulators in Vibrios, the involvement of Qrr sRNAs in V. parahaemolyticus is largely unknown. Here, we carried out the Qrr5 deletion mutant and utilized a proteomic method to describe global proteomic alterations in response to Qrr5 deletion. A total of 297 significantly expressed proteins were determined between the Qrr5 deletion mutant and wild-type strain, among which 137 proteins were upregulated and 160 proteins were downregulated. The upregulated proteins principally participated in membrane transporters and signal transcription, while the downregulated proteins participated in the two-component system and transcription factor binding. Notably, transcriptional regulator LysR, outer membrane protein OmpA, and conjugal transfer protein TraA-related proteins were upregulated, causing the promotion of autoaggregation ability and growth competition ability against E. coli. This study provides insights into the regulatory network of sRNA in this bacterium, which will facilitate further explorations of important biological processes in pathogenic bacteria. SIGNIFICANCE: sRNA Qrr5 is an important regulator involved in bacterial multiple physiological processes, including auto-aggregation and growth competition among food-borne pathogens Vibrio parahaemolyticus. Here, utilizing a TMT-labeling proteomic approach, we identified 137 proteins were upregulated and 160 proteins were downregulated between the Qrr5 deletion mutant and wild-type strain. The upregulated proteins were involved in membrane transporters and signal transcription, while downregulated proteins were involved in the two-component system and transcription factor binding. Moreover, the LysR, OmpA, and TraA proteins were significantly upregulated, causing the promotion of autoaggregation and commensal growth competition ability. The mechanism of how Qrr5 regulates the targeted genes remains unclarified and need great efforts to explore.

Separation of Glycosylated OmpA-Like Proteins from Porphyromonas gingivalis and Tannerella forsythia

OmpA-like proteins located in the outer bacterial membrane are potential virulence factors from the major periodontal pathogens Porphyromonas gingivalis and Tannerella forsythia. Our previous studies have shown that OmpA-like proteins are glycosylated by O-linked N-acetylglucosamine (O-GlcNAc) and are strongly reactive to wheat germ agglutinin (WGA) lectin, which shows sugar specificity to GlcNAc. Utilizing this property, we have developed a separation method for OmpA-like proteins by affinity chromatography using WGA lectin-agarose. The purity of enriched native OmpA-like proteins were confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Coomassie Brilliant Blue (CBB) staining. More importantly, the purified OmpA-like proteins formed a unique trimeric structure keeping their bioactivity intact. In this chapter, we describe a detailed procedure to separate OmpA-like proteins, which may be used to further progress the biological studies of OmpA-like proteins.

Adhesion of anaerobic periodontal pathogens to extracellular matrix proteins

Extracellular matrix (ECM) proteins are highly abundant in the human body and can be found in various tissues, most prominently in connective tissue and basement membrane. For invasive bacterial pathogens, these structures function as physical barriers that block access to underlying tissues. The ability to bind and degrade these barriers is important for the establishment of infections and migration to other body sites. In the oral cavity, the ECM and the basement membrane (BM) are important components of the Junctional epithelium (JE) that closes the gap between the teeth surface and the mucosa. In periodontitis, the JE is breached by invading pathogenic bacteria, particularly strict anaerobic species. In periodontitis, invading microorganisms induce an unregulated and destructive host response through polymicrobial synergism and dysbiosis that attracts immune cells and contributes to the destruction of connective tissue and bone in the periodontal pocket. Colonization of the periodontal pocket is the first step to establish this infection, and binding to ECM is a major advantage in this site. Several species of strict anaerobic bacteria are implicated in acute and chronic periodontitis, and although binding to ECM proteins was studied in these species, few adhesins were identified so far, and the mechanisms involved in adhesion are largely unidentified. This review summarizes the data available on the interaction of strict anaerobic bacteria and components of the ECM.

Lanthanide-Binding Tags for 3D X-ray Imaging of Proteins in Cells at Nanoscale Resolution

We report the application of lanthanide-binding tags (LBTs) for two- and three-dimensional X-ray imaging of individual proteins in cells with a sub-15 nm beam. The method combines encoded LBTs, which are tags of minimal size (ca. 15-20 amino acids) affording high-affinity lanthanide ion binding, and X-ray fluorescence microscopy (XFM). This approach enables visualization of LBT-tagged proteins while simultaneously measuring the elemental distribution in cells at a spatial resolution necessary for visualizing cell membranes and eukaryotic subcellular organelles.

Tannerella forsythia strains display different cell-surface nonulosonic acids: biosynthetic pathway characterization and first insight into biological implications

Tannerella forsythia is an anaerobic, Gram-negative periodontal pathogen. A unique O-linked oligosaccharide decorates the bacterium's cell surface proteins and was shown to modulate the host immune response. In our study, we investigated the biosynthesis of the nonulosonic acid (NulO) present at the terminal position of this glycan. A bioinformatic analysis of T. forsythia genomes revealed a gene locus for the synthesis of pseudaminic acid (Pse) in the type strain ATCC 43037 while strains FDC 92A2 and UB4 possess a locus for the synthesis of legionaminic acid (Leg) instead. In contrast to the NulO in ATCC 43037, which has been previously identified as a Pse derivative (5-N-acetimidoyl-7-N-glyceroyl-3,5,7,9-tetradeoxy-l-glycero-l-manno-NulO), glycan analysis of strain UB4 performed in this study indicated a 350-Da, possibly N-glycolyl Leg (3,5,7,9-tetradeoxy-d-glycero-d-galacto-NulO) derivative with unknown C5,7 N-acyl moieties. We have expressed, purified and characterized enzymes of both NulO pathways to confirm these genes’ functions. Using capillary electrophoresis (CE), CE–mass spectrometry and NMR spectroscopy, our studies revealed that Pse biosynthesis in ATCC 43037 essentially follows the UDP-sugar route described in Helicobacter pylori, while the pathway in strain FDC 92A2 corresponds to Leg biosynthesis in Campylobacter jejuni involving GDP-sugar intermediates. To demonstrate that the NulO biosynthesis enzymes are functional in vivo, we created knockout mutants resulting in glycans lacking the respective NulO. Compared to the wild-type strains, the mutants exhibited significantly reduced biofilm formation on mucin-coated surfaces, suggestive of their involvement in host-pathogen interactions or host survival. This study contributes to understanding possible biological roles of bacterial NulOs.

Disulfide Bonds: A Key Modification in Bacterial Extracytoplasmic Proteins

Disulfide bonds are a common posttranslational modification that contributes to the folding and stability of extracytoplasmic proteins. Almost all organisms, from eukaryotes to prokaryotes, have evolved enzymes to make and break these bonds. Accurate and efficient disulfide bond formation can be vital for protein function; therefore, the enzymes that catalyze disulfide bond formation are involved in multiple biological processes. Recent advances clearly show that oral bacteria also have the ability to from disulfide bonds, and this ability has an effect on a range of dental plaque-related phenotypes. In the gram-positive Streptococcus gordonii, the ability to form disulfide bonds affected autolysis, extracellular DNA release, biofilm formation, genetic competence, and bacteriocin production. In Actinomyces oris, disulfide bond formation is needed for pilus assembly, coaggregation, and biofilm formation. In other gram-positive bacteria, such as Enterococcus faecalis, disulfide bonds are formed in secreted bacteriocins and required for activity. In these oral bacteria, the enzymes that catalyze the disulfide bonds are quite diverse and share little sequence homology, but all contain a CXXC catalytic active site motif and a conserved C-terminal cis-proline, signature features of a thiol-disulfide oxidoreductase. Emerging evidence also indicates that gram-negative oral bacteria, such as Porphyromonas gingivalis and Tannerella forsythia, use disulfide bonds to stabilize their outer membrane porin proteins. Bioinformatic screens reveal that these gram-negative bacteria carry genes coding for thiol-disulfide oxidoreductases in their genomes. In conclusion, disulfide bond formation in oral bacteria is an emerging field, and the ability to form disulfide bonds plays an important role in dental plaque formation and fitness for the bacteria.

Identification of OmpA-Like Protein of Tannerella forsythia as an O-Linked Glycoprotein and Its Binding Capability to Lectins

Bacterial glycoproteins are associated with physiological and pathogenic functions of bacteria. It remains unclear whether bacterial glycoproteins can bind to specific classes of lectins expressed on host cells. Tannerella forsythia is a gram-negative oral anaerobe that contributes to the development of periodontitis. In this study, we aimed to find lectin-binding glycoproteins in T. forsythia. We performed affinity chromatography of wheat germ agglutinin, which binds to N-acetylglucosamine (GlcNAc) and sialic acid (Sia), and identified OmpA-like protein as the glycoprotein that has the highest affinity. Mass spectrometry revealed that OmpA-like protein contains O-type N-acetylhexosamine and hexose. Fluorometry quantitatively showed that OmpA-like protein contains Sia. OmpA-like protein was found to bind to lectins including E-selectin, P-selectin, L-selectin, Siglec-5, Siglec-9, Siglec-10, and DC-SIGN. The binding of OmpA-like protein to these lectins, except for the Siglecs, depends on the presence of calcium. N-acetylneuraminic acid (NeuAc), which is the most abundant Sia, inhibited the binding of OmpA-like protein to all of these lectins, whereas GlcNAc and mannose only inhibited the binding to DC-SIGN. We further found that T. forsythia adhered to human oral epithelial cells, which express E-selectin and P-selectin, and that this adhesion was inhibited by addition of NeuAc. Moreover, adhesion of an OmpA-like protein-deficient T. forsythia strain to the cells was reduced compared to that of the wild-type strain. Our findings indicate that OmpA-like protein of T. forsythia contains O-linked sugar chains that can mediate interactions with specific lectins. This interaction is suggested to facilitate adhesion of T. forsythia to the surface of host cells.

Role of Extracellular Structures of Escherichia coli O157:H7 in Initial Attachment to Biotic and Abiotic Surfaces

Infection by human pathogens through the consumption of fresh, minimally processed produce and solid plant-derived foods is a major concern of the U.S. and global food industries and of public health services. Enterohemorrhagic Escherichia coli O157:H7 is a frequent and potent foodborne pathogen that causes severe disease in humans. Biofilms formed by E. coli O157:H7 facilitate cross-contamination by sheltering pathogens and protecting them from cleaning and sanitation operations. The objective of this research was to determine the role that several surface structures of E. coli O157:H7 play in adherence to biotic and abiotic surfaces. A set of isogenic deletion mutants lacking major surface structures was generated. The mutant strains were inoculated onto fresh spinach and glass surfaces, and their capability to adhere was assessed by adherence assays and fluorescence microscopy methods. Our results showed that filament-deficient mutants bound to the spinach leaves and glass surfaces less strongly than the wild-type strain did. We mimicked the switch to the external environment-during which bacteria leave the host organism and adapt to lower ambient temperatures of cultivation or food processing-by decreasing the temperature from 37°C to 25°C and 4°C. We concluded that flagella and some other cell surface proteins are important factors in the process of initial attachment and in the establishment of biofilms. A better understanding of the specific roles of these structures in early stages of biofilm formation can help to prevent cross-contaminations and foodborne disease outbreaks.

Characterization of Mannheimia haemolytica biofilm formation in vitro

Mannheimia haemolytica is the primary bacterial agent in the bovine respiratory disease complex. It is thought that M. haemolytica colonizes the tonsillar crypts of cattle as a commensal and subsequently descends into the lungs to cause disease. Many bacterial species persist in the host as biofilms. There is limited information about the ability of M. haemolytica to form biofilms. The aim of this study was to develop an in vitro model for M. haemolytica biofilm formation. We found that M. haemolytica required at least 36 h to form robust biofilms on plastic in vitro when incubated in RPMI-1640 tissue culture medium at 37 °C, with maximal biofilm formation being evident at 48 h. Biofilm formation was inhibited by adding the monosaccharides d(+) galactose and d(+) mannose to the growth medium. Addition of antibodies to the M. haemolytica surface protein OmpA also reduced biofilm formation. Upon evaluating the macromolecules within the biofilm extracellular polymeric substance we found it contained 9.7 μg/cm(2) of protein, 0.81 μg/cm(2) of total carbohydrate, and 0.47 μg/cm(2) of extracellular DNA. Furthermore, proteinase K treatment significantly decreased biofilms (P<0.05) while α-amylase and micrococcal nuclease decreased biofilms to a lesser extent. M. haemolytica biofilm cells were more resistant than planktonic cells to the antibiotics florfenicol, gentamicin, and tulathromycin. These results provide evidence that M. haemolytica can form biofilms, which could contribute to its ability to persist as a commensal in the bovine upper respiratory tract.

Characterization of wheat germ agglutinin lectin-reactive glycosylated OmpA-like proteins derived from Porphyromonas gingivalis

Glycosylation is one of the common posttranslational modifications in eukaryotes. Recently, glycosylated proteins have also been identified in prokaryotes. A few glycosylated proteins, including gingipains, have been identified in Porphyromonas gingivalis, a major pathogen associated with chronic periodontitis. However, no other glycosylated proteins have been found. The present study identified glycoproteins in P. gingivalis cell lysates by lectin blotting. Whole-cell lysates reacted with concanavalin A (ConA), Lens culinaris agglutinin (LCA), Phaseolus vulgaris erythroagglutinin (PHA-E4), and wheat germ agglutinin (WGA), suggesting the presence of mannose-, N-acetylgalactosamine-, or N-acetylglucosamine (GlcNAc)-modified proteins. Next, glycoproteins were isolated by ConA-, LCA-, PHA-E4-, or WGA-conjugated lectin affinity chromatography although specific proteins were enriched only by the WGA column. Mass spectrometry analysis showed that an OmpA-like, heterotrimeric complex formed by Pgm6 and Pgm7 (Pgm6/7) was the major glycoprotein isolated from P. gingivalis. Deglycosylation experiments and Western blotting with a specific antibody indicated that Pgm6/7 was modified with O-GlcNAc. When whole-cell lysates from P. gingivalis mutant strains with deletions of Pgm6 and Pgm7 were applied to a WGA column, homotrimeric Pgm7, but not Pgm6, was isolated. Heterotrimeric Pgm6/7 had the strongest affinity for fibronectin of all the extracellular proteins tested, whereas homotrimeric Pgm7 showed reduced binding activity. These findings suggest that the heterotrimeric structure is important for the biological activity of glycosylated WGA-binding OmpA-like proteins in P. gingivalis.

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.

Major membrane protein TDE2508 regulates adhesive potency in Treponema denticola

The cultivation and genetic manipulation of Treponema denticola, a Gram-negative oral spirochaeta associated with periodontal diseases, is still challenging. In this study, we formulated a simple medium based on a commercially available one, and established a transformation method with high efficiency. We then analyzed proteins in a membrane fraction in T. denticola and identified 16 major membrane-associated proteins, and characterized one of them, TDE2508, whose biological function was not yet known. Although this protein, which exhibited a complex conformation, was presumably localized in the outer membrane, we did not find conclusive evidence that it was exposed on the cell surface. Intriguingly, a TDE2508-deficient mutant exhibited significantly increased biofilm formation and adherent activity on human gingival epithelial cells. However, the protein deficiency did not alter autoaggregation, coaggregation with Porphyromonas gingivalis, hemagglutination, cell surface hydrophobicity, motility, or expression of Msp which was reported to be an adherent molecule in this bacteria. In conclusion, the major membrane protein TDE2508 regulates biofilm formation and the adhesive potency of T. denticola, although the underlying mechanism remains unclear.

Localization and function of the accessory protein Mfa3 in Porphyromonas gingivalis Mfa1 fimbriae

The fimbriae of Porphyromonas gingivalis, the causative agent of periodontitis, have been implicated in various aspects of pathogenicity, such as colonization, adhesion and aggregation. Porphyromonas gingivalis ATCC 33277 has two adhesins comprised of the FimA and Mfa1 fimbriae. We characterized the PGN0289 (Mfa3) protein, which is one of the three accessory proteins of Mfa1 fimbriae in P. gingivalis. The Mfa3 protein was present in two different sizes, 40 and 43 kDa, in the cell. The 43-kDa and 40-kDa Mfa3 were detected largely in the inner membrane and the outer membrane, respectively. Purified Mfa1 fimbriae contained the 40-kDa Mfa3 alone. Furthermore, the 40-kDa Mfa3 started with the Ala(44) residue of the deduced amino acid sequence, indicating that the N-terminal region of the nascent protein expressed from the mfa3 gene is processed in the transport step from the inner membrane into fimbriae. Immuno-electron microscopy revealed that Mfa3 localized at the tip of the fimbrial shaft. Interestingly, deletion of the mfa3 gene resulted in the absence of other accessory proteins, PGN0290 and PGN0291, in the purified Mfa1 fimbriae, suggesting that Mfa3 is required for integration of PGN0290 and PGN0291 into fimbriae. A double mutant of mfa3 and fimA genes (phenotype Mfa1 plus, FimA minus) showed increased auto-aggregation and biofilm formation similar to a double mutant of mfa1 and fimA genes (phenotype Mfa1(-) , FimA(-) ). These findings suggest that the tip protein Mfa3 of the Mfa1 fimbriae may function in the integration of accessory proteins and in the colonization of P. gingivalis.

The versatile in situ gene expression of an Epsilonproteobacteria-dominated biofilm from a hydrothermal chimney

The Epsilonproteobacteria, including members of the genus Sulfurovum, are regarded as important primary producers in hydrothermal systems. However, their in situ gene expression in this habitat has so far not been investigated. We report a metatranscriptomic analysis of a Sulfurovum-dominated biofilm from one of the chimneys at the Loki's Castle hydrothermal system, located at the Arctic Mid Ocean Ridge. Transcripts involved in hydrogen oxidation, oxidation of sulfur species, aerobic respiration and denitrification were abundant and mostly assigned to Sulfurovum, indicating that members of this genus utilize multiple chemical energy sources simultaneously for primary production. Sulfurovum also seemed to have a diverse expression of transposases, potentially involved in horizontal gene transfer. Other transcripts were involved in CO₂ fixation by the reverse TCA cycle, the CRISPR-Cas system, heavy metal resistance, and sensing and responding to changing environmental conditions. Through pyrosequencing of PCR amplified 16S rRNA genes, the Sulfurovum-dominated biofilm was compared with another biofilm from the same chimney, revealing a large shift in the community structure of Epsilonproteobacteria-dominated biofilms over a few metres.

Leptospiral outer membrane protein microarray, a novel approach to identification of host ligand-binding proteins

Leptospirosis is a zoonosis with worldwide distribution caused by pathogenic spirochetes belonging to the genus Leptospira. The leptospiral life cycle involves transmission via freshwater and colonization of the renal tubules of their reservoir hosts. Infection requires adherence to cell surfaces and extracellular matrix components of host tissues. These host-pathogen interactions involve outer membrane proteins (OMPs) expressed on the bacterial surface. In this study, we developed an Leptospira interrogans serovar Copenhageni strain Fiocruz L1-130 OMP microarray containing all predicted lipoproteins and transmembrane OMPs. A total of 401 leptospiral genes or their fragments were transcribed and translated in vitro and printed on nitrocellulose-coated glass slides. We investigated the potential of this protein microarray to screen for interactions between leptospiral OMPs and fibronectin (Fn). This approach resulted in the identification of the recently described fibronectin-binding protein, LIC10258 (MFn8, Lsa66), and 14 novel Fn-binding proteins, denoted Microarray Fn-binding proteins (MFns). We confirmed Fn binding of purified recombinant LIC11612 (MFn1), LIC10714 (MFn2), LIC11051 (MFn6), LIC11436 (MFn7), LIC10258 (MFn8, Lsa66), and LIC10537 (MFn9) by far-Western blot assays. Moreover, we obtained specific antibodies to MFn1, MFn7, MFn8 (Lsa66), and MFn9 and demonstrated that MFn1, MFn7, and MFn9 are expressed and surface exposed under in vitro growth conditions. Further, we demonstrated that MFn1, MFn4 (LIC12631, Sph2), and MFn7 enable leptospires to bind fibronectin when expressed in the saprophyte, Leptospira biflexa. Protein microarrays are valuable tools for high-throughput identification of novel host ligand-binding proteins that have the potential to play key roles in the virulence mechanisms of pathogens.

Identification and characterization of novel glycoproteins involved in growth and biofilm formation by Porphyromonas gingivalis

Porphyromonas gingivalis has been implicated as a major pathogen associated with chronic periodontitis. To extend our knowledge of post-translational protein glycosylation in P. gingivalis, a proteomic analysis involving two-dimensional polyacrylamide gel electrophoresis combined with carbohydrate staining and mass spectrometry was performed. Four novel glycoproteins, PGN0743, PGN0876, PGN1513 and PGN0729, in P. gingivalis ATCC 33277 were identified. These four identified glycoproteins possess a range of biochemical activities and cellular localization. PGN0743 contains a sequence motif identifying it as a FKBP-type cis-trans isomerase, which has activity usually associated with chaperone functions. PGN0876 and PGN1513 contain tetratricopeptide repeat domains that mediate protein-protein interactions. PGN0729 encodes the outer membrane protein 41 precursor, which was previously identified as Pgm6, and is homologous to the OmpA protein in Escherichia coli. Several different types of glycoprotein were identified, suggesting that P. gingivalis possesses a general mechanism for protein glycosylation. PGN0743-deficient and PGN0876-deficient mutants were constructed to examine the role(s) of the two identified glycoproteins. Both mutants showed a decreased growth rate under nutrient-limited conditions and reduced biofilm formation activity. These results suggest that the novel glycoproteins PGN0743 and PGN0876 play an important role in the growth and colonization of P. gingivalis.