Type VI Secretion
How else could your cell deliver a toxin to a nearby competitor? As usual, nature has provided another, even more entertaining, option: the poison dart gun. Many diderm bacteria, including Myxococcus xanthus like this, use type VI secretion systems (T6SSs) to launch effector proteins into neighboring cells. The effectors vary, from toxins that cause lysis to factors that promote biofilm formation. The target range of the T6SS is similarly broad, including monoderm and diderm bacteria and eukaryotic cells.
This loaded T6SS consists of a hollow outer tube, with a narrower dart inside (⇩). The effector protein is loaded at the tip of the dart, where the machine is anchored in the cell envelope. In a few cells, including this one, we see additional filaments flanking the primed T6SS. They are lacking in other cells even of the same species, and their identity and function remain unknown.