Some types of bacteria have evolved spring-loaded molecular daggers with which to attack nearby cells.
The “type VI secretion system”, found in roughly one-quarter of all bacteria with two membranes, comprises an 80-atom-long “nanoweapon” which contracts quickly, firing a dagger into the surrounding medium and, possibly, into a nearby cell.
The type VI secretion is similar to the one used by bacteriophages – viruses that infect bacteria.
For a video of the phenomenon in action, follow this link.
Read more at California Institute of Technology