Computer logic usually consists of electronic switches. Recently, scientists have been exploring alternative means for conducting calculations, from optical computing to operations based on the manipulation of chemicals in a test tube. Writing this week in the Journal of Biological Engineering, a group of scientists reports that they have created specially-modified E. coli bacteria capable of performing one specific type of calculation (a puzzle known as the 'pancake flipping problem.') We'll talk with one of the researchers about the prospects for biologically-based computing, and what calculating bacteria might be useful for.