We're covered in bacteria every day. They help us digest our food and protect our skin, and they're potentially a great medical tool -- but only if we can control them. Scientists think they have taken the first step by engineering bacteria that can live in a swarm, but die when they try to escape individually to new areas. The right bacteria can help treat infections, out-breed bad bacteria and help regulate functions like digestion. Scientists at Duke University have taken advantage of the fact that bacteria can change their behaviour when they're in large enough concentrations, and have engineered bacteria that rely on dense populations (often in enclosed spaces) to survive. Their findings are published in the latest issue of Molecular Systems Biology.
To make these bacteria -- dubbed "swarmbots" because they can only survive in a swarm -- the researchers started with a harmless strain of E. coli bacteria. These bacteria were engineered to produce a signalling molecule called N-Acyl homoserine lactone, or AHL.
The phenomenon is known as "quorum sensing". Bacteria produce AHL when they come together in large enough concentrations. In response to the molecule, some bacteria shorten their tentacle-like appendages and modify their movement, so they all stick together as a slime-like biofilm. Other bacteria, like the luminescent Vibrio fischeri, only produce light when they're in groups, and use AHL as a signal to know when they have a so-called "quorum".
The swarmbots respond to AHL by producing a protein that is resistant to antibiotics. They stop producing it when they are alone. During the experiment, scientists bathed bacteria in a pool of antibiotics. Regular bacteria, constantly producing the protein, broke out of their small capsule and spread. Swarmbots, however, stayed together. If any one bacteria broke out, it would stop being able to make its "antidote" to antibiotics and die off.
Scientists hope that these bacteria might be useful for all kinds of medical applications. The bacteria could make other proteins or even drugs, in response to the living body around them. When a system weakens enough to allow them to reach a population density, they might make chemicals that regulate the system and bring their own numbers down again.