Angelika Schmalzl

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B7 Functional analysis of bacterial Type VI effectors in EBI3-dependend regulation of enteric infection and inflammation

Principal investigator
Stefan Wirtz & Markus Neurath

Mentor
Steffen Backert

The role of type VI secretion system (T6SS) effectors for the composition of the intestinal microbiome during intestinal infections and inflammatory bowel disease

The intestinal tract contains a complex microbial ecosystem that has important metabolic and host-protective functions. Therefore, its integrity is crucial and compositional changes or a dysbiotic intestinal microbiome have been associated with the pathology of gut as well as extra-intestinal disorders. Effector proteins released through specific secretion systems play key roles for the interactions of bacterial cells with the host organism but also with other microorganisms. These effectors mediate interbacterial antagonism and were shown to be crucial for bacterial fitness within specific ecological niches. As a consequence, secreted mediators potentially define the composition of the intestinal microbiome and remain its integrity. On the contrary, enteric pathogens are able to negatively influence and disrupt this integrity through the secretion of antibacterial factors to decrease colonization resistance and settle in the intestine.
Citrobacter rodentium is an enteric pathogen that is widely used as a rodent model for infections with EHEC/EPEC and inflammatory bowel diseases in humans. C. rodentium harbors a recently described protein transport machinery: the type VI secretion system (T6SS) that enables the delivery of effector proteins to the periplasm of recipient bacteria or directly into a target cell. Through generation of C. rodentium single gene-mutants of T6SS-relevant structure proteins, a functional T6SS was shown to be required for an effective C. rodentium colonization of the mouse gastrointestinal tract since infection with T6SS-mutants led to less severe inflammation and pathology. 16S-based next generation sequencing of genetic material isolated from stool samples of infected mice revealed that wt C. rodentium is successfully reprogramming the gastrointestinal microbiome since the spectrum of microbiota found in with wt C. rodentium infected mice was diminished compared to stool of mice infected with T6SS-mutant strains. However, the mechanisms of T6SS-mediated interbacterial antagonism are not completely understood. The aim of my project is to characterize the function of the two potential C. rodentium T6SS effector proteins Cts1D and Cts1F in vitro and to analyze their relevance for interbacterial competition in vivo and in vitro through construction of gene-specific deletion mutants. Not only the mechanism of T6SS-based interbacterial antagonism is incompletely understood, but also its relevance in the context of future infections or intestinal inflammatory diseases that are possibly triggered by the reduction of the compositional complexity are aimed to be studied. Hence, initial studies revealed that the T6SS-mediated changes of the intestinal microbiome increase the susceptibility of mice for experimentally-induced intestinal inflammation. In addition, one task of the project is to translate the knowledge obtained from the C. rodentium T6SS to clinically relevant strains of the genus Enterobacter that carries a T6SS gene cluster that is highly similar to the C. rodentium T6SS. For this purpose, I want to create similar Enterobacter T6SS single gene-mutants to study the functional relevance of this secretion system in in vivo and in vitro experiments.

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Presentations

October 2016 8th Annual Retreat, Erlangen School of Molecular Communication, Schloss Schney, Lichtenfels, Germany
“The role of type VI secretion system (T6SS) effectors for the composition of the intestinal microbiome during intestinal infections and inflammatory bowel disease”
Talk