Bacterial Type 4 Secretion Systems (T4SS) represent remarkable nanomachines that mediate the transfer of various substrates from a donor to a recipient cell. T4SS have two pivotal functions : 1) firstly, they facilitate the exchange of genetic material among prokaryotes, a process referred to as "conjugation". Conjugation is the major driver of genome dynamics and evolution, including playing a critical role in the rapid dissemination of antibiotic resistance. 2) Secondly, certain pathogenic bacteria exploit T4SS to deliver virulence proteins into both prokaryotic and eukaryotic cells, thereby instigating severe diseases including chronic infections and cancers. In this talk, I will present the first high-resolution structure of a colossal 2.8 MegaDalton T4SS complex involved in pilus biogenesis, solved using cryo-EM and validated by state-of-art co-evolution analysis (AlphaFOLD2). Secondly, I will present the cryo-EM structure of the substrate recruiting platform employed by the pathogenic bacterium Legionella pneumophila. This structure not only showcases the high-resolution architecture of the platform but also unveils a two effectors recruitment mechanistic models.​