Bacteria pretty much have nano-sized versions of anything humans can come up with. That list somehow includes knife-wielding street gangs, as some bacteria shoot poison-tipped molecular "daggers" at each other, proving that nothing does awesome violence quite like bacteria.

The firing mechanism for this dagger is tiny, even by bacterial standards — it's the equivalent of just eighty atoms long. The bacteria can assemble the weapon anywhere on their bodies, fire a dagger through their cell membrane, and then take apart the firing tube so that it can be deployed again elsewhere on the cell. The dagger can be used to pierce other nearby cells in order to inject proteins as part of an attack. To get an up close look at just how the daggers work, you can check out the video up top.

These molecular daggers were first spotted accidentally by researchers at Caltech, who were using a powerful electron microscope to probe bacterial samples in as close to their native state as possible. While studying how the bacteria prepare their genetic material for reproduction, the researchers noticed a long tube that seemed to span the width of the bacterium's body.

They had no idea what these mysterious tubes were, but they soon connected the tubes with a phenomenon known as the type VI secretion system, a biological process seen in about a quarter of bacteria with two membranes. The thing is, while scientists already knew the end result of this system — the bacteria send out proteins — they had no idea how it actually worked. This tubing and these molecular daggers provide the answer to that enigma. Caltech biologist Grant Jensen remarks on the craziness of this discovery:

"People aren't surprised that animals have really interesting ways to hurt each other-snakes have venom, bears have claws. 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."

The firing mechanism resembles that of bacteria-infecting viruses known as bacteriophages, which shoot a projectile similar to the dagger out of their tails. The bacteria's daggers likely wouldn't have been spotted without the special type of electron microscope used by the researchers, as the lengthy preparation process used in more traditional electron microscopes apparently destroys any trace of the tubing - which explains why we're only just seeing this insane nano-weapon now.

Via Nature. Image by . Video by Nature/Everett Kane/M. Basler/M. Pilhofer/G.P. Henderson/G.J. Jensen/J. Mekalanos.