Type VI secretion system effector proteins: effective weapons for bacterial competitiveness

The Type VI secretion system (T6SS) is a protein translocation nanomachine widespread among Gram-negative bacteria and used as a means to deliver effectors directly into target bacterial or eukaryotic cells. These effectors have a wide variety of functions within target cells that ultimately help the secreting cell gain a competitive fitness advantage. Here, we discuss the different ways in which these effectors can be delivered by the T6SS and the diverse mechanisms by which they exert their noxious action upon recipient cells. We also highlight the existence of roles for T6SS effectors beyond simply the killing of neighbouring cells.