A new delivery domain for type VI secretion system toxins

Bacteria often interact with rival bacteria or with eukaryotic hosts and predators. All of these interactions can be affected by toxic proteins, called effectors, that are delivered directly into a neighboring cell by the bacterial type VI secretion system (T6SS). This contractile injection system shoots an effector-decorated, arrow-like structure out of the cell with great force; the arrow penetrates the neighboring cell and deploys the effectors inside it. Although many T6SS effector families have been identified, many still await discovery. I will discuss a new, widespread class of T6SS effectors that share an N-terminal domain named RIX. I will show that RIX targets proteins for secretion via T6SS, and that it is fused to polymorphic C-terminal domains that function as antibacterial toxins, anti-eukaryotic toxins, or as tethers for toxins encoded by other genes.