Lysins are phage-encoded enzymes that degrade the peptidoglycan layer of bacterial cell walls. They hold promise as alternatives to antibiotics, particularly in combating rising antimicrobial resistance. However, lysin research remains largely empirical, relying on resource-intensive screenings with limited generalizability. This highlights the need for fundamental studies to address unresolved questions about lysin structure, function and regulation. In this project, I will study regulatory mechanisms and interactions between specific lysin modules in their natural phage context in view of their impact on phage fitness, with a particular focus on the lysis step. Therefore, I will make use of recent technological advances to efficiently edit phage genomes to study the function of genes and their structure-function relationships. These insights will result in a paradigm shift towards a more refined understanding of the modularity of phage lysins than our current simplistic view. Ultimately, my research will drive the development of improved next-generation antimicrobial lysins with decoupled regulatory and lytic functions, offering a rationalized and de-risked approach to lysin R&D pipelines.