Svoboda, S. | Search bioRxiv

bioRxiv2024

Semilichen - an unjustly neglected symbiotic system between green biofilms and true lichens

- Symbiotic systems of photosynthetic microorganisms and fungi are widespread in terrestrial biomes and lichens are probably the most advanced and complex. Conversely, the least complex systems are "green biofilms" with a completely unexplored mycobiome. We describe here a new system intermediate between green biofilms and lichens - semilichens. - Light and fluorescence microscopy, eDNA sequencing, molecular phylogeny, Chlorophyll a fluorescence and 13C labelling/metabolomics were used to study algal and fungal identity, morphology and physiology of the symbiosis. - Tight contact between algae and a single predominant fungus (mycobiont) is revealed in semilichens. The algae are from the symbiotic lineages of Trebouxiophyceae and Ulvophyceae, the fungi belong to Arthoniomycetes, Dothideomycetes, Eurotiomycetes, Lecanoromycetes and Lichinomycetes. Algae are alive and perform substantial photosynthetic activity. 13C labelled photosynthates are partially converted into specific fungal polyols (arabitol, mannitol) demonstrating the C-flow from algae to fungi. - The new symbiotic system was defined and compared with other terrestrial algal-fungal symbioses. It is characterized by minimalist environmental requirements and extremely low production of biomass. As a result, it also inhabits environments unfavourable for lichens. Our research supports the hypothesis that the long-term existence of algae and fungi in terrestrial conditions affected by frequent and repeated drying is likely dependent on their mutual coexistence.

physiology↗

bioRxiv2018

Natural Secretory Immunoglobulins Enhance Norovirus Infection

Secretory immunoglobulins (SIg) are a first line of mucosal defense by the host. They are secreted into the gut lumen via the polymeric immunoglobulin receptor (pIgR) where they bind to antigen and are transported back across the FAE via M cells. Noroviruses are highly prevalent, enteric pathogens that cause significant morbidity, mortality and economic losses worldwide. Murine norovirus (MNV) exploits microfold (M) cells to cross the lymphoid follicle-associated epithelium (FAE) and infect the underlying population of immune cells. However, whether natural, innate SIg can protect against norovirus infection remains unknown. To investigate the role of natural SIg during murine norovirus pathogenesis, we used pIgR-deficient animals, which lack SIg in the intestinal lumen. Contrary to other enteric pathogens, acute MNV replication was significantly reduced in the gastrointestinal tract of pIgR-deficient animals compared to controls, despite increased numbers of dendritic cells, macrophages, and B cells in the Peyers patch, established MNV target cell types. Also, natural SIg did not alter MNV FAE binding or FAE crossing into the lymphoid follicle. Instead, further analysis revealed enhanced baseline levels of the antiviral molecules interferon gamma (IFN{gamma}) and inducible nitric oxide synthase (iNOS) in the small intestine of naive pIgR-deficient animals compared to controls. Removing the microbiota equalized IFN{gamma} and iNOS transcript levels as well as MNV viral loads in germ-free pIgR KO mice compared to germ-free controls. These data are consistent with a model whereby SIg sensing reduces pro-inflammatory, antiviral molecules, which facilitates intestinal homeostasis but thereby promotes MNV infection. In conclusion, these findings demonstrate that natural SIg are not protective during norovirus infection in mice and represent another example of indirect modulation of enteric virus pathogenesis by the microbiota.

microbiology↗