Glycobiology of a novel Tannerella species

The globally occurring gum disease periodontitis critically involves the pathogenic bacterium Tannerella forsythia acting as a late colonizer of a polymicrobial biofilm, commonly known as dental plaque. We found that this bacterium has a unique cell surface protein glycosylation, which underpins its pathogenicity by influencing the relationship with other biofilm bacteria and the host through dedicated glycobiological and glycoimmunological interactions; a specific sugar acid (nonulosonic acid) seems to be pivotal to these interactions. A comparison of all publicly available genome sequences of periodontitis-associated T. forsythia strains revealed the presence of a distinct gene cluster that underlays protein glycosylation. In contrast, the genome of the novel, putative periodontal health-associated Tannerella species BU063, which is the closest phylogenetic relative to T. forsythia, has a different glycosylation gene cluster lacking genes for sugar acid biosynthesis. We hypothesize that an altered glycome contributes to the difference of periodontal pathogenesis by Tannerella sp. BU063 and provides a new foundation to further understand the genome evolution and mechanisms of bacteria-host interaction in closely related oral microbes with different pathogenicity potential. Initial data indicate differences in surface-layer protein glycosylation and immunogenicity of Tannerella sp. BU063 compared to T. forsythia. Our novel procedures for cultivation and genetic manipulation of Tannerella sp. BU063 make detailed glycobiological investigations possible. We will investigate the glycoinfrastructure of the Tannerella sp. BU063 cell envelope and determine possible implications for the bacterium`s biofilm lifestyle and interaction with the host. Methods include anaerobic bacterial cultivation, mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (NMR) for glycan structure elucidation, glycoproteomics, genetic manipulation, immune response profiling, biofilm techniques, and imaging. This project generates glycobiology information on a novel oral Tannerella species and aims at delineating glycobiology-mediated mechanisms that could support the association of this bacterium with periodontal health. In relation to the glycobiology knowledge of the pathogenic relative T. forsythia, this project might provide novel insight into the pathogenesis of periodontitis and pinpoint novel therapeutic and prophylaxis approaches against the disease. It also furthers our knowledge on the Bacteroidetes phylum, to which Tannerella species are affiliated, since this bacterial phylum is prominent not only in the oral but also in the gut microbiome. This project is a collaboration between Christina Schäffer (principal investigator; microbiology, glycobiology, biofilm, imaging), Friedrich Altmann (MS), Markus Blaukopf (NMR), all Universität für Bodenkultur, Vienna, Austria, Oleh Andrukhov (immunology; Medical University, Vienna, Austria), and Georgios N. Belibasakis (interaction studies with selected host cells; Karolinska Institutet, Huddinge, Sweden).

Understanding the molecular language of oral bacteria-New insights into health and disease: The human mouth harbours one of the most complex microbial ecosystems in the body. The balance between health-associated and disease-causing bacteria in the oral cavity is not accidental-it is actively shaped by molecular signals on bacterial surfaces. This project has generated fundamental new knowledge about how oral bacteria present themselves to their environment, how they interact with host tissues, and what distinguishes a harmful bacterium from a harmless one. A central focus was Tannerella serpentiformis, a health-associated oral bacterium and close relative of Tannerella forsythia-a key driver of periodontitis, one of the most prevalent chronic inflammatory diseases worldwide. By deciphering the complex sugar structures that coat the surface of T. serpentiformis, the project revealed that this bacterium carries highly elaborate, branched glycan chains bearing rare chemical modifications not previously described in oral bacteria. Strikingly, the absence of a specific sugar residue-a nonulosonic acid found on the surface of the pathogen T. forsythia-appears to be a molecular hallmark distinguishing health-associated from disease-causing Tannerella species. This finding opens new avenues for understanding how bacteria evade or engage the immune system. Beyond surface chemistry, the project investigated the three-dimensional architecture of the crystalline protein coat-the S-layer-that envelops T. serpentiformis. Using state-of-the-art electron microscopy and computational structure prediction, including artificial intelligence-based protein modelling, the team reconstructed how the two S-layer glycoproteins of T. serpentiformis assemble into a symmetric lattice with a central pore. This architecture, informed for the first time by experimentally verified glycosylation data, provides a plausible molecular blueprint for how multi-protein S-layers are organised-a question that has remained unresolved for decades. The project also examined how T. serpentiformis behaves within complex oral biofilms alongside other bacteria, including the notorious pathogen Porphyromonas gingivalis. Remarkably, T. serpentiformis was found to suppress biofilm overgrowth and outcompete its pathogenic relative T. forsythia-suggesting an active protective role in maintaining a healthy oral microbiome. Complementary studies on host cell interactions confirmed that T. serpentiformis is significantly less invasive than T. forsythia and triggers a more robust immune response, consistent with its health-associated status. Together, the results of this project advance our molecular understanding of how bacterial surface structures-particularly glycans and S-layer proteins-govern microbial community dynamics, host recognition, and immune modulation in the oral cavity. These insights lay the groundwork for future strategies aimed at promoting beneficial oral microbiomes and may ultimately contribute to novel approaches for the prevention and treatment of periodontitis.