Activity, abundance and localization of eukaryotic proteins can be regulated through covalent attachment of ubiquitin and ubiquitin-like moieties. Ubiquitination is important in various aspects of immunity. Pathogens utilize host ubiquitination for the suppression of immune signalling and reprogramming host processes to promote microbial life. They deliver so-called effector molecules into host cells, which functionally or structurally resemble components of the host ubiquitination machinery utilizing this enzymatic process or they secrete molecules to inhibit ubiquitin-mediated degradation. Since prokaryotic pathogens lack a classical ubiquitination system, effector mimicry of components of the ubiquitin machinery could be achieved through gene flow. Horizontal gene transfer allows pathogenic bacteria to access ubiquitination enzymes from a potential host, while lateral gene transfer recruits components from another pathogen providing spread within the microbial community. Additionally, convergent evolution can shape bacterial proteins to acquire ubiquitination functions.