As intracellular bacteria, Chlamydia trachomatis interfere with host cell trafficking and signalling pathways to maintain their replicative niche, a membrane-bound vacuole called inclusion. The chlamydial deubiquitinase Cdu1 integrates into the inclusion membrane, with its catalytically active site facing the host cell cytosol. We could previously show that Cdu1 stabilizes Mcl-1, a major inhibitor of apoptotic signalling which prevents host cell apoptosis of Chlamydia-infected cells. Furthermore, Cdu1 protects inclusions from ubiquitination as well as the recruitment of autophagy receptors, influences the redistribution of the Golgi around the inclusion and its loss affects chlamydial development. The aim of this project is to investigate the interaction of Chlamydia with the host ubiquitin system during infection, identify further substrates and to uncover the mechanism of target specificity of Cdu1..