Type VI secretion delivers bacteriolytic effectors to target cells

The type VI secretion system (T6SS) is a protein-export machine that is present in about one-quarter of all sequenced bacteria. Bacteria can use this system to deliver toxic effector proteins in a contact-dependent manner to other bacterial cells. However, what these proteins do once their destination is reached has remained largely unknown. It is now shown that the opportunistic human pathogen Pseudomonas aeruginosa uses its T6SS to kill competing Gram-negative bacteria by injecting them with two peptidoglycan-degradative enzymes, the effector proteins Tse1 and Tse3. P. aeruginosa protects itself from these effectors by expressing immunity proteins that bind the toxins.