Encounters between two strains of bacteria can bear a striking resemblance to humanity's wars, or those of ants. These epic battles have now been filmed using a species common in the human intestine, revealing that cells at the front line call in reinforcements from those less directly exposed to invasion.
Escherichia coli, better known as E. coli, is a bacterium that comes in many hostile varieties. In the struggle to control a bit of gut, E. coli produces toxins to repel rivals, sometimes at the cost of the animal whose intestine is the war zone. Toxin release is triggered by DNA damage but is sometimes produced spontaneously as a pre-emptive strike. The targets can be other microbial species, or competing E. coli strains. Cells produce immunity proteins that protect themselves against their own chemical weapons but can easily be killed by those of other other E. coli strains.
When two E. coli varieties encounter one another, each will release its own chemical weapons to try to dispose of the other. An individual cell facing attack cannot produce enough toxins for victory, so responds to attack by sending a message that calls others of its kind to help. The result looks like something out of World War I as the two colonies engage in trench warfare, with a no cell zone in between, where only those resistant to the enemy's weapons survive.
“Our research shows that what appear to be simple organisms can function in a very sophisticated manner. Their behavior is more complex than we have previously given them credit for,” said Professor Kevin Foster of the University of Oxford in a statement. “Much like social insects, such as honey bees and wasps and social animals like birds and mammals who use alarm calls, when under predation, they are capable of generating a coordinated attack.”
The observations have been published in Current Biology, and a video of two strains of bacteria, modified so they glow green when releasing toxins, can be seen below. We think it would be better with the Game of Thrones music played over the top, like a real-life version of this video of slime molds.
Strategies also vary by strain. Some engage in total war, expending all the resources they can on wiping out their opponents, while others prioritize other things in the hope it will all blow over.
Just how sophisticated can bacterial warfare get? Are they capable of forming alliances to rally support from other strains, or even different species, to stop the most aggressive varieties? We don't yet know, but Foster and his co-authors showed how easily the diversity emerges by inducing a small number of targeted mutations in a particular strain.