Bacteria have evolved different systems for secreting proteins into the fluid around them or into other cells. Some, for example, have syringe-like exterior structures that can pierce other cells and inject proteins. Another system, called a type VI secretion system, is found in about a quarter of all bacteria with two membranes. Despite being common, researchers have not understood how it works. Now a team, co-led by researchers at the California Institute of Technology (Caltech), has figured out the structure of the type VI secretion system apparatus and proposed how it might work—by shooting spring-loaded poison molecular daggers.
"People aren't surprised that animals have really interesting ways to hurt each other—snakes have venom, bears have claws," says Grant Jensen, professor of biology at Caltech and coleader of the study. "But they might be surprised that a single cell within one of those animals' bodies is still 100 times larger than the bacterial cells we're talking about, and yet the bacterial cells contain weapons that are so sophisticated. That's the marvel."