Rearchers of the Harvard Medical School built a 2 feet by 4 feet (61 x 122 cm) large petri-dish to visualize the evolution of bacteria. Their experiment induces mutations in E. coli bacteria by exposing them to gradually increasing concentrations of antibiotics.
Their assembly consists of a large glass tank with a thick agar at its bottom and a thinner agar on top of it, which acts as a mobility layer, allowing the bacteria to move around in the dish. The bottom layer is divided into 9 bands, which are treated with gradually increasing concentrations of antibiotics: No antibiotics in the outer bands, one time the lethal concentration for the bacteria in the second most outer bands, with each band increasing the concentration tenfold until it reaches 1000 times the lethal dose in the center band.
Then the E. coli bacteria enter the playing field. Every time they reach the frontier to a new band, they are forced to develop new mutations to survive in the harsher environment. When they finally reach the center band after 11 days, they are able to withstand a thousand times more antibiotics than their wild type could survive. The way the researchers set it up, their experiment lets you watch the evolutional pedigree of each mutation branch in a flat-out astonishing way. Enjoy the science below!