Davidson College researchers genetically engineered the bacterium E. coli to coax its DNA into computing a classic mathematical puzzle known as the burned pancake problem.

The problem: start with a stack of pancakes of varying sizes burned on one side, and try to get the pancakes into order from largest to smallest — all burned side down — through a series of flips. The figurative spatula can flip at any point in the stack, but has to include all the pancakes above.

The researchers inserted the Hin recombinase enzyme into E. coli. The enzyme could then flip segments of E. coli’s DNA that are marked by genetic flags. The researchers designed these segments so that, when lined up in the correct order like pancakes stacked from biggest to smallest (burned side down, of course), the DNA spells out the code for a gene that gives the bacterium resistance to an antibiotic.

That way, applying the antibiotic to the colony of engineered bacteria killed all of the bacteria that had not yet solved the puzzle. Only those that had “stacked their pancakes” would survive. Measuring how long it took the bacteria to reach the solution indicated how many flips were required.