No abstract

The intestinal microbiota influences mammalian host physiology in health and disease locally in the gut but also in organs devoid of direct contact with bacteria such as the liver and brain. Extracellular vesicles (EVs) or outer membrane vesicles (OMVs) released by microbes are increasingly recognized for their potential role as biological shuttle systems for inter‐kingdom communication. However, physiologically relevant evidence for the transfer of functional biomolecules from the intestinal microbiota to individual host cells by OMVs in vivo is scarce. By introducing Escherichia coli engineered to express Cre‐recombinase ( E. coli Cre ) into mice with a Rosa26.tdTomato ‐reporter background, we leveraged the Cre‐LoxP system to report the transfer of bacterial OMVs to recipient cells in vivo. Colonizing the intestine of these mice with E. coli Cre , resulted in Cre‐recombinase induced fluorescent reporter gene‐expression in cells along the intestinal epithelium, including intestinal stem cells as well as mucosal immune cells such as macrophages. Furthermore, even far beyond the gut, bacterial‐derived Cre induced extended marker gene expression in a wide range of host tissues, including the heart, liver, kidney, spleen, and brain. Together, our findings provide a method and proof of principle that OMVs can serve as a biological shuttle system for the horizontal transfer of functional biomolecules between bacteria and mammalian host cells.

Corynebacterium ulcerans is an emerging pathogen, which is increasingly recognized as an etiological agent of diphtheria, but can also evoke ulcers of the skin and systemic infections in humans. Besides man, the bacteria can colonize a wide variety of different animals, including cattle and pet animals, which might serve as a reservoir for human infections. In this study, surface-located proteins and the exoproteome of two Corynebacterium ulcerans strains were analyzed, since these may have key roles in the interaction of the pathogen with host cells. Strain 809 was isolated from a fatal case of human respiratory tract infection, while strain BR-AD22 was isolated from a nasal swap of an asymptomatic dog. While a very similar pattern of virulence factors was observed in the culture supernatant and surface protein fractions of the two strains, proteome analyses revealed a higher stability of 809 cells compared to strain BR-AD22. During exponential growth, 17% of encoded proteins of strain 809 were detectable in the medium, while 38% of the predicted proteins encoded by the BR-AD22 chromosome were found. Furthermore, the data indicate differential expression of phospholipase D and a cell wall-associated hydrolase, since these were only detected in strain BR-AD22.

Here we provide compelling evidence that inflammation in a murine model of Crohn’s disease–like inflammation is characterized by an immune reaction presumably directed at a disease-relevant microflora in a genetically susceptible host with impaired mucosal barrier function and bacterial clearance.

During viral infections viruses express molecules that interfere with the host-cell death machinery and thus inhibit cell death responses. For example the viral FLIP (vFLIP) encoded by Kaposi’s sarcoma-associated herpesvirus interacts and inhibits the central cell death effector, Caspase-8. In order to analyze the impact of anti-apoptotic viral proteins, like vFlip, on liver physiology in vivo, mice expressing vFlip constitutively in hepatocytes (vFlipAlbCre+) were generated. Transgenic expression of vFlip caused severe liver tissue injury accompanied by massive hepatocellular necrosis and inflammation that finally culminated in early postnatal death of mice. On a molecular level, hepatocellular death was mediated by RIPK1-MLKL necroptosis driven by an autocrine TNF production. The loss of hepatocytes was accompanied by impaired bile acid production and disruption of the bile duct structure with impact on the liver-gut axis. Notably, embryonic development and tissue homeostasis were unaffected by vFlip expression. In summary our data uncovered that transgenic expression of vFlip can cause severe liver injury in mice, culminating in multiple organ insufficiency and death. These results demonstrate that viral cell death regulatory molecules exhibit different facets of activities beyond the inhibition of cell death that may merit more sophisticated in vitro and in vivo analysis.