Porphyromonas gingivalis and the pathogenesis of Alzheimer's disease.

The cause of Alzheimer's disease (AD), and the pathophysiological mechanisms involved, remain major unanswered questions in medical science. Oral bacteria, especially those species associated with chronic periodontitis and particularly Porphyromonas gingivalis, are being linked causally to AD pathophysiology in a subpopulation of susceptible individuals. P. gingivalis produces large amounts of proteolytic enzymes, haem and iron capture proteins, adhesins and internalins that are secreted and attached to the cell surface and concentrated onto outer membrane vesicles (OMVs). These enzymes and adhesive proteins have been shown to cause host tissue damage and stimulate inflammatory responses. The ecological and pathophysiological roles of P. gingivalis OMVs, their ability to disperse widely throughout the host and deliver functional proteins lead to the proposal that they may be the link between a P. gingivalis focal infection in the subgingivae during periodontitis and neurodegeneration in AD. P. gingivalis OMVs can cross the blood brain barrier and may accelerate AD-specific neuropathology by increasing neuroinflammation, plaque/tangle formation and dysregulation of iron homeostasis, thereby inducing ferroptosis leading to neuronal death and neurodegeneration.

Temporal development of the infant oral microbiome.

The human oral microbiome is becoming recognized as playing roles in health and disease well beyond the oral cavity over the lifetime of the individual. The oral microbiome is hypothesized to result from specific colonization events followed by a reproducible and ordered development of complex bacterial communities. Colonization events, proliferation, succession and subsequent community development are dependent on a range of host and environmental factors, most notably the neonate diet. It is now becoming apparent that early childhood and prenatal influences can have long term effects on the development of human oral microbiomes. In this review, the temporal development of the infant human oral microbiome is examined, with the effects of prenatal and postnatal influences and the roles of specific bacteria. Dietary and environmental factors, especially breastfeeding, have a significant influence on the development of the infant oral microbiome. The evidence available regarding the roles and functions of early colonizing bacteria is still limited, and gaps in knowledge where further research is needed to elucidate these specific roles in relation to health and disease still exist.

Feasibility and development of a cariogenic diet scale for epidemiological research.

BACKGROUND: Diet cariogenicity plays a major role as both a protective and risk factor in the development of early childhood caries (ECC). AIM: Develop a scale measuring the cariogenicity of foods and beverages and employ it to describe the cariogenicity of young children's diets and predict dental caries outcomes. DESIGN: Scores of cariogenicity and consumption frequency were applied to food frequency questionnaire (FFQ) collected from an Australian children's cohort study with three time-points of data. One-way ANOVA, with post hoc Tukey test compared mean cariogenic scale measured at 18 months between the subsample of children with caries classification at age 5 years. RESULTS: At 6 months, children's mean cariogenic score was 10.05, increasing to 34.18 at 12 and 50.00 at 18 months. Mean cariogenic scale score at 18 months was significantly higher in children with advanced disease at 5 years (mean scale score: 59.0 ± 15.9) compared to those that were healthy (mean score 47.7 ± 17.5, P = 0.007) or had mild-moderate disease (mean score 48.2 ± 17.3, P = 0.008). CONCLUSIONS: The cariogenic diet scale provides a useful indication of the increasing cariogenicity of children's diets with age and highlights the incorporation of discretionary choice foods and beverages into the diets of young children much earlier than nutritionally recommended.

Outer Membrane Vesicle Proteome of Porphyromonas gingivalis Is Differentially Modulated Relative to the Outer Membrane in Response to Heme Availability.

Porphyromonas gingivalis is an anaerobic, Gram-negative oral pathogen associated with chronic periodontitis. P. gingivalis has an obligate requirement for heme, which it obtains from the host. Heme availability has been linked to disease initiation and progression. In this study we used continuous culture of the bacterium to determine the effect of heme limitation and excess on the P. gingivalis proteome. Four biological replicates of whole cell lysate (WCL) and outer membrane vesicle (OMV) samples were digested with trypsin and analyzed by tandem mass spectrometry and MaxQuant label-free quantification. In total, 1211 proteins were quantified, with 108 and 49 proteins significantly changing in abundance more than 1.5-fold ( p < 0.05) in the WCLs and OMVs, respectively. The proteins most upregulated in response to heme limitation were those involved in binding and transporting heme, whereas the four proteins most upregulated under the heme-excess condition constitute a putative heme efflux system. In general, the protein abundance ratios obtained for OMVs and WCLs agreed, indicating that changes to the OM protein composition are passed onto OMVs; however, 16 proteins were preferentially packaged into OMVs under one condition more than the other. In particular, moonlighting cytoplasmic proteins were preferentially associated with OMVs under heme excess.

Porphyromonas gingivalis Type IX Secretion Substrates Are Cleaved and Modified by a Sortase-Like Mechanism.

The type IX secretion system (T9SS) of Porphyromonas gingivalis secretes proteins possessing a conserved C-terminal domain (CTD) to the cell surface. The C-terminal signal is essential for these proteins to translocate across the outer membrane via the T9SS. On the surface the CTD of these proteins is cleaved prior to extensive glycosylation. It is believed that the modification on these CTD proteins is anionic lipopolysaccharide (A-LPS), which enables the attachment of CTD proteins to the cell surface. However, the exact site of modification and the mechanism of attachment of CTD proteins to the cell surface are unknown. In this study we characterized two wbaP (PG1964) mutants that did not synthesise A-LPS and accumulated CTD proteins in the clarified culture fluid (CCF). The CTDs of the CTD proteins in the CCF were cleaved suggesting normal secretion, however, the CTD proteins were not glycosylated. Mass spectrometric analysis of CTD proteins purified from the CCF of the wbaP mutants revealed the presence of various peptide/amino acid modifications from the growth medium at the C-terminus of the mature CTD proteins. This suggested that modification occurs at the C-terminus of T9SS substrates in the wild type P. gingivalis. This was confirmed by analysis of CTD proteins from wild type, where a 648 Da linker was identified to be attached at the C-terminus of mature CTD proteins. Importantly, treatment with proteinase K released the 648 Da linker from the CTD proteins demonstrating a peptide bond between the C-terminus and the modification. Together, this is suggestive of a mechanism similar to sortase A for the cleavage and modification/attachment of CTD proteins in P. gingivalis. PG0026 has been recognized as the CTD signal peptidase and is now proposed to be the sortase-like protein in P. gingivalis. To our knowledge, this is the first biochemical evidence suggesting a sortase-like mechanism in Gram-negative bacteria.

Porphyromonas gulae Has Virulence and Immunological Characteristics Similar to Those of the Human Periodontal Pathogen Porphyromonas gingivalis.

Periodontitis is a significant problem in companion animals, and yet little is known about the disease-associated microbiota. A major virulence factor for the human periodontal pathogen Porphyromonas gingivalis is the lysyl- and arginyl-specific proteolytic activity of the gingipains. We screened several Porphyromonas species isolated from companion animals-P. asaccharolytica, P. circumdentaria, P. endodontalis, P. levii, P. gulae, P. macacae, P. catoniae, and P. salivosa-for Lys- and Arg-specific proteolytic activity and compared the epithelial and macrophage responses and induction of alveolar bone resorption of the protease active species to that of Porphyromonas gingivalis Only P. gulae exhibited Lys-and Arg-specific proteolytic activity. The genes encoding the gingipains (RgpA/B and Kgp) were identified in the P. gulae strain ATCC 51700 and all publicly available 12 draft genomes of P. gulae strains. P. gulae ATCC 51700 induced levels of alveolar bone resorption in an animal model of periodontitis similar to those in P. gingivalis W50 and exhibited a higher capacity for autoaggregation and binding to oral epithelial cells with induction of apoptosis. Macrophages (RAW 264.7) were found to phagocytose P. gulae ATCC 51700 and the fimbriated P. gingivalis ATCC 33277 at similar levels. In response to P. gulae ATCC 51700, macrophages secreted higher levels of cytokines than those induced by P. gingivalis ATCC 33277 but lower than those induced by P. gingivalis W50, except for the interleukin-6 response. Our results indicate that P. gulae exhibits virulence characteristics similar to those of the human periodontal pathogen P. gingivalis and therefore may play a key role in the development of periodontitis in companion animals.

Porphyromonas gingivalis and Treponema denticola exhibit metabolic symbioses.

Porphyromonas gingivalis and Treponema denticola are strongly associated with chronic periodontitis. These bacteria have been co-localized in subgingival plaque and demonstrated to exhibit symbiosis in growth in vitro and synergistic virulence upon co-infection in animal models of disease. Here we show that during continuous co-culture a P. gingivalis:T. denticola cell ratio of 6∶1 was maintained with a respective increase of 54% and 30% in cell numbers when compared with mono-culture. Co-culture caused significant changes in global gene expression in both species with altered expression of 184 T. denticola and 134 P. gingivalis genes. P. gingivalis genes encoding a predicted thiamine biosynthesis pathway were up-regulated whilst genes involved in fatty acid biosynthesis were down-regulated. T. denticola genes encoding virulence factors including dentilisin and glycine catabolic pathways were significantly up-regulated during co-culture. Metabolic labeling using 13C-glycine showed that T. denticola rapidly metabolized this amino acid resulting in the production of acetate and lactate. P. gingivalis may be an important source of free glycine for T. denticola as mono-cultures of P. gingivalis and T. denticola were found to produce and consume free glycine, respectively; free glycine production by P. gingivalis was stimulated by T. denticola conditioned medium and glycine supplementation of T. denticola medium increased final cell density 1.7-fold. Collectively these data show P. gingivalis and T. denticola respond metabolically to the presence of each other with T. denticola displaying responses that help explain enhanced virulence of co-infections.

Bacterial interactions in pathogenic subgingival plaque.

Chronic periodontitis has a polymicrobial biofilm aetiology. Polymicrobial biofilms are complex, dynamic microbial communities formed by two or more bacterial species that are important for the persistence and proliferation of participating microbes in the environment. Interspecies adherence, which often involves bacterial surface-associated molecules, and communications are essential in the spatial and temporal development of a polymicrobial biofilm, which in turn is necessary for the overall fitness of a well-organized multispecies biofilm community. In the oral cavity, interactions between key oral bacterial species, including Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia, are essential for the progression of chronic periodontitis. In vivo, P. gingivalis and T. denticola are frequently found to co-exist in deep periodontal pockets and have been co-localized to the superficial layers of subgingival plaque as microcolony blooms adjacent to the pocket epithelium, suggesting possible interbacterial interactions that contribute towards disease. The motility and chemotactic ability of T. denticola, although not considered as classic virulence factors, are likely to be important in the synergistic biofilm formation with P. gingivalis. In vitro, P. gingivalis and T. denticola display a symbiotic relationship in nutrient utilization and growth promotion. Together these data suggest there is an intimate relationship between these two species that has evolved to enhance their survival and virulence.

Protein substrates of a novel secretion system are numerous in the Bacteroidetes phylum and have in common a cleavable C-terminal secretion signal, extensive post-translational modification, and cell-surface attachment.

The secretion of certain proteins in Porphyromonas gingivalis is dependent on a C-terminal domain (CTD). After secretion, the CTD is cleaved prior to extensive modification of the mature protein, probably with lipopolysaccharide, therefore enabling attachment to the cell surface. In this study, bioinformatic analyses of the CTD demonstrated the presence of three conserved sequence motifs. These motifs were used to construct Hidden Markov Models (HMMs) that predicted 663 CTD-containing proteins in 21 fully sequenced species of the Bacteroidetes phylum, while no CTD-containing proteins were predicted in species outside this phylum. Further HMM searching of Cytophaga hutchinsonii led to a total of 171 predicted CTD proteins in that organism alone. Proteomic analyses of membrane fractions and culture fluid derived from P. gingivalis and four other species containing predicted CTDs (Parabacteroides distasonis, Prevotella intermedia, Tannerella forsythia, and C. hutchinsonii) demonstrated that membrane localization, extensive post-translational modification, and CTD-cleavage were conserved features of the secretion system. The CTD cleavage site of 10 different proteins from 3 different species was determined and found to be similar to the cleavage site previously determined in P. gingivalis, suggesting that homologues of the C-terminal signal peptidase (PG0026) are responsible for the cleavage in these species.

Association Between Oral Bacteria and Alzheimer's Disease: A Systematic Review and Meta-Analysis.

BACKGROUND: Pre-clinical evidence implicates oral bacteria in the pathogenesis of Alzheimer's disease (AD), while clinical studies show diverse results. OBJECTIVE: To comprehensively assess the association between oral bacteria and AD with clinical evidence. METHODS: Studies investigating the association between oral bacteria and AD were identified through a systematic search of six databases PubMed, Embase, Cochrane Central Library, Scopus, ScienceDirect, and Web of Science. Methodological quality ratings of the included studies were performed. A best evidence synthesis was employed to integrate the results. When applicable, a meta-analysis was conducted using a random-effect model. RESULTS: Of the 16 studies included, ten investigated periodontal pathobionts and six were microbiome-wide association studies. Samples from the brain, serum, and oral cavity were tested. We found over a ten-fold and six-fold increased risk of AD when there were oral bacteria (OR = 10.68 95% CI: 4.48-25.43; p < 0.00001, I2 = 0%) and Porphyromonas gingivalis (OR = 6.84 95% CI: 2.70-17.31; p < 0.0001, I2 = 0%) respectively in the brain. While AD patients exhibited lower alpha diversity of oral microbiota than healthy controls, the findings of bacterial communities were inconsistent among studies. The best evidence synthesis suggested a moderate level of evidence for an overall association between oral bacteria and AD and for oral bacteria being a risk factor for AD. CONCLUSION: Current evidence moderately supports the association between oral bacteria and AD, while the association was strong when oral bacteria were detectable in the brain. Further evidence is needed to clarify the interrelationship between both individual species and bacterial communities and the development of AD.

Differential proteomic analysis of a polymicrobial biofilm.

Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia exist in a polymicrobial biofilm associated with chronic periodontitis. The aim of this study was to culture these three species as a polymicrobial biofilm and to determine proteins important for bacterial interactions. In a flow cell all three species attached and grew as a biofilm; however, after 90 h of culture P. gingivalis and T. denticola were closely associated and dominated the polymicrobial biofilm. For comparison, planktonic cultures of P. gingivalis and T. denticola were grown separately in continuous culture. Whole cell lysates were subjected to SDS-PAGE, followed by in-gel proteolytic H2¹6O/H2¹8O labeling. From two replicates, 135 and 174 P. gingivalis proteins and 134 and 194 T. denticola proteins were quantified by LC-MALDI TOF/TOF MS. The results suggest a change of strategy in iron acquisition by P. gingivalis due to large increases in the abundance of HusA and HusB in the polymicrobial biofilm while HmuY and other iron/haem transport systems decreased. Significant changes in the abundance of peptidases and enzymes involved in glutamate and glycine catabolism suggest syntrophy. These data indicate an intimate association between P. gingivalis and T. denticola in a biofilm that may play a role in disease pathogenesis.

The outer membrane protein LptO is essential for the O-deacylation of LPS and the co-ordinated secretion and attachment of A-LPS and CTD proteins in Porphyromonas gingivalis.

Protein substrates of a novel secretion system of Porphyromonas gingivalis contain a conserved C-terminal domain (CTD) essential for secretion and attachment to the cell surface. Inactivation of lptO (PG0027) or porT produced mutants that lacked surface protease activity and an electron-dense surface layer. Both mutants showed co-accumulation of A-LPS and unmodified CTD proteins in the periplasm. Lipid profiling by mass spectrometry showed the presence of both tetra- and penta-acylated forms of mono-phosphorylated lipid A in the wild-type and porT mutant, while only the penta-acylated forms of mono-phosphorylated lipid A were found in the lptO mutant, indicating a specific role of LptO in the O-deacylation of mono-phosphorylated lipid A. Increased levels of non-phosphorylated lipid A and the presence of novel phospholipids in the lptO mutant were also observed that may compensate for the missing mono-phosphorylated tetra-acylated lipid A in the outer membrane (OM). Molecular modelling predicted LptO to adopt a ß-barrel structure characteristic of an OM protein, supported by the enrichment of LptO in OM vesicles. The results suggest that LPS deacylation by LptO is linked to the co-ordinated secretion of A-LPS and CTD proteins by a novel secretion and attachment system to form a structured surface layer.

Lactoferrin inhibits Porphyromonas gingivalis proteinases and has sustained biofilm inhibitory activity.

Porphyromonas gingivalis is a bacterial pathogen associated with chronic periodontitis that results in destruction of the tooth's supporting tissues. The major virulence determinants of P. gingivalis are its cell surface Arg- and Lys-specific cysteine proteinases, RgpA/B and Kgp. Lactoferrin (LF), an 80-kDa iron-binding glycoprotein found in saliva and gingival crevicular fluid, is believed to play an important role in innate immunity. In this study, bovine milk LF displayed proteinase inhibitory activity against P. gingivalis whole cells, significantly inhibiting both Arg- and Lys-specific proteolytic activities. LF inhibited the Arg-specific activity of purified RgpB, which lacks adhesin domains, and also inhibited the same activity of the RgpA/Kgp proteinase-adhesin complexes in a time-dependent manner, with a first-order inactivation rate constant (k(inact)) of 0.023 min(-1) and an inhibitor affinity constant (K(I)) of 5.02 µM. LF inhibited P. gingivalis biofilm formation by >80% at concentrations above 0.625 µM. LF was relatively resistant to hydrolysis by P. gingivalis cells but was cleaved into two major polypeptides (53 and 33 kDa) at R(284) to S(285), as determined by in-source decay mass spectrometry; however, these polypeptides remained associated with each other and retained inhibitory activity. The biofilm inhibitory activity of LF against P. gingivalis was not attributed to direct antibacterial activity, as LF displayed little growth inhibitory activity against planktonic cells. As the known RgpA/B and Kgp inhibitor N-α-p-tosyl-l-lysine chloromethylketone also inhibited P. gingivalis biofilm formation, the antibiofilm effect of LF may at least in part be attributable to its antiproteinase activity.

Breastmilk influences development and composition of the oral microbiome.

Background: Human microbiomes assemble in an ordered, reproducible manner yet there is limited information about early colonisation and development of bacterial communities that constitute the oral microbiome. Aim: The aim of this study was to determine the effect of exposure to breastmilk on assembly of the infant oral microbiome during the first 20 months of life. Methods: The oral microbiomes of 39 infants, 13 who were never breastfed and 26 who were breastfed for more than 10 months, from the longitudinal VicGeneration birth cohort study, were determined at four ages. In total, 519 bacterial taxa were identified and quantified in saliva by sequencing the V4 region of the bacterial 16S rRNA genes. Results: There were significant differences in the development of the oral microbiomes of never breastfed and breastfed infants. Bacterial diversity was significantly higher in never breastfed infants at 2 months, due largely to an increased abundance of Veillonella and species from the Bacteroidetes phylum compared with breastfed infants. Conclusion: These differences likely reflect breastmilk playing a prebiotic role in selection of early-colonising, health-associated oral bacteria, such as the Streptococcus mitis group. The microbiomes of both groups became more heterogenous following the introduction of solid foods.

Porphyromonas gingivalis cysteine proteinase inhibition by kappa-casein peptides.

Porphyromonas gingivalis is a major pathogen associated with chronic periodontitis, an inflammatory disease of the supporting tissues of the teeth. The Arg-specific (RgpA/B) and Lys-specific (Kgp) cysteine proteinases of P. gingivalis are major virulence factors for the bacterium. In this study κ-casein(109-137) was identified in a chymosin digest of casein as an inhibiting peptide of the P. gingivalis proteinases. The peptide was synthesized and shown to inhibit proteolytic activity associated with P. gingivalis whole cells, purified RgpA-Kgp proteinase-adhesin complexes, and purified RgpB proteinase. The peptide κ-casein(109-137) exhibited synergism with Zn(II) against both Arg- and Lys-specific proteinases. The active region for inhibition was identified as κ-casein(117-137) using synthetic peptides. Kinetic studies revealed that κ-casein(109-137) inhibits in an uncompetitive manner. A molecular model based on the uncompetitive action and its synergistic ability with Zn(II) was developed to explain the mechanism of inhibition. Preincubation of P. gingivalis with κ-casein(109-137) significantly reduced lesion development in a murine model of infection.

Bugs and Brains, the Gut and Mental Health Study: a mixed-methods study investigating microbiota composition and function in anxiety, depression and irritable bowel syndrome.

INTRODUCTION: Research has highlighted relationships between the micro-organisms that inhabit our gastrointestinal tract (oral and gut microbiota) with host mood and gastrointestinal functioning. Mental health disorders and functional gastrointestinal disorders co-occur at high rates, although the mechanisms underlying these associations remain unclear. The Bugs and Brains Study aims to investigate complex relationships between anxiety/depression and irritable bowel syndrome (IBS) in two ways. First, its primary component will compare the gut and oral microbiota in females with anxiety/depression and/or IBS relative to controls, and investigate underlying physiological, endocrine and immune factors, as well as associations with diet and psychosocial factors. In an ancillary component, the study will also investigate gastrointestinal and mental health symptoms in a larger sample, and explore relationships with diet, exercise, oral health, substance use, medical history, early life adversity and psychosocial factors. METHODS AND ANALYSIS: The Bugs and Brains Study aims to recruit 160 females to the primary component: (1) 40 controls; (2) 40 participants with a depressive/anxiety disorder, but no IBS; (3) 40 participants with IBS, but no depressive/anxiety disorder and (4) 40 participants with both depressive/anxiety disorder and IBS. Participation is completed within 1 month, and involves comprehensive questionnaires, anthropometrics, a diagnostic clinical interview, collection of two saliva samples, and stool, urine and hair samples. This study aims to use a systems biology approach to characterise oral and gut microbial composition and function using 16S rRNA gene sequencing and nuclear MR spectroscopy. As part of the ancillary component, it will collect questionnaire data from 1000 participants aged 18-40 years, capturing mental health, gastrointestinal health, oral health, diet and psychosocial factors. ETHICS AND DISSEMINATION: Approval was granted by the University of Melbourne Human Research Ethics Committee (#1749221). All participants voluntarily provided informed consent. Results will be published in peer-reviewed journals and presented at scientific conferences.

Major proteins and antigens of Treponema denticola.

Treponema denticola is a Gram-negative, motile, asaccharolytic, anaerobic spirochaete which along with Porphyromonas gingivalis and Tannerella forsythia has been shown to form a bacterial consortium called the Red Complex that is strongly associated with the clinical progression of chronic periodontitis. T. denticola was grown in continuous culture in a complex medium with a mean generation time of 15.75 h. Samples from two different membrane-enriched preparations and a cytoplasm-enriched preparation were separated by two-dimensional gel electrophoresis and the proteins identified by MALDI-TOF/TOF mass spectrometry. In total, 219 non-redundant proteins were identified including numerous virulence factors, lipoproteins, ABC transporter proteins and enzymes involved in the metabolism of nine different amino acids of which glycine seems to be of particular importance. Novel findings include the identification of several abundant peptide uptake systems, and the identification of three flagellar filament outer layer proteins. Two-dimensional Western blot analysis using sera from mice immunized with formalin-killed T. denticola cells suggested that Msp, PrcA, OppA, OppA10, MglB, TmpC and several flagellar filament proteins are antigenic.

Treponema denticola biofilm-induced expression of a bacteriophage, toxin-antitoxin systems and transposases.

Treponema denticola is an oral spirochaete that has been strongly associated with chronic periodontitis. The bacterium exists as part of a dense biofilm (subgingival dental plaque) accreted to the tooth. To determine T. denticola gene products important for persistence as a biofilm we developed a continuous-culture biofilm model and conducted a genome-wide transcriptomic analysis of biofilm and planktonic cells. A total of 126 genes were differentially expressed with a fold change of 1.5 or greater. This analysis identified the upregulation of putative prophage genes in the T. denticola 35405 genome. Intact bacteriophage particles were isolated from T. denticola and circular phage DNA was detected by PCR analysis. This represents the first, to our knowledge, functional bacteriophage isolated from T. denticola, which we have designated varphitd1. In biofilm cells there was also an upregulation of genes encoding several virulence factors, toxin-antitoxin systems and a family of putative transposases. Together, these data indicate that there is a higher potential for genetic mobility in T. denticola when growing as a biofilm and that these systems are important for the biofilm persistence and therefore virulence of this bacterium.

Metabolic cooperativity between Porphyromonas gingivalis and Treponema denticola.

BACKGROUND:  Porphyromonas gingivalis and Treponema denticola are proteolytic periodontopathogens that co-localize in polymicrobial subgingival plaque biofilms, display in vitro growth symbiosis and synergistic virulence in animal models of disease. These symbioses are underpinned by a range of metabolic interactions including cooperative hydrolysis of glycine-containing peptides to produce free glycine, which T. denticola uses as a major energy and carbon source. OBJECTIVE:  To characterize the P. gingivalis gene products essential for these interactions. Methods: The P. gingivalis transcriptome exposed to cell-free T. denticola conditioned medium was determined using RNA-seq. P. gingivalis proteases potentially involved in hydrolysis of glycine-containing peptides were identified using a bioinformatics approach. RESULTS:  One hundred and thirty-twogenes displayed differential expression, with the pattern of gene expression consistent with succinate cross-feeding from T. denticola to P. gingivalis and metabolic shifts in the P. gingivalis folate-mediated one carbon superpathway. Interestingly, no P. gingivalis proteases were significantly up-regulated. Three P. gingivalis proteases were identified as candidates and inactivated to determine their role in the release of free glycine. P. gingivalis PG0753 and PG1788 but not PG1605 are involved in the hydrolysis of glycine-containing peptides, making free glycine available for T. denticola utilization. CONCLUSION:  Collectively these metabolic interactions help to partition resources and engage synergistic interactions between these two species.

Oral microbiome composition, but not diversity, is associated with adolescent anxiety and depression symptoms.

PURPOSE: Depression and anxiety are highly prevalent disorders, whose significant burden is compounded by the presence of oral disease. Mental health disorders and oral health may be associated via changes to the oral microbiome, involving increased pro-inflammatory communication and cortisol in saliva. The present study provides the first culture-independent investigation of the oral microbiome considering depression and anxiety symptoms in adolescence, a critical age where these conditions begin to emerge and co-occur. It also investigates whether inflammation and cortisol moderate these relationships. METHODS: Participants (N = 66) aged 14-18 years (69.70% female) self-reported oral health, depression and anxiety symptoms, and collected saliva samples across two days. Saliva was assayed for cortisol and C-reactive protein (CRP), and used for 16S rRNA gene sequencing to estimate the oral microbiome. Multivariate statistical analyses examined associations. RESULTS: Overall diversity of the oral microbiome did not differ between adolescents by anxiety or depression grouping (low versus high symptoms), and was not associated with symptom measures. Depression and anxiety symptoms were instead associated with differential abundance of specific bacterial taxa, including Spirochaetaceae, Actinomyces, Treponema, Fusobacterium and Leptotrichia spp. Several host mood-microbial relationships were moderated by proposed mechanisms, including salivary cortisol and CRP. CONCLUSIONS: Oral microbiome composition, but not diversity, was associated with adolescent anxiety and depression symptoms. Longitudinal studies considering these associations would improve mechanistic understanding. This research indicates that adolescence remains an essential developmental period to identify early targets for intervention.