Ridges in biofilms grown on petri dishes have sparked a fundamental discovery in how cells self assemble into three dimensional structures. Gürol Süel, a systems biologist at the University of California, San Diego,wanted to learn more about the coupling of physical and biological factors determining an organism’s shape, so he turned to one of the simplest living systems he could think of: the biofilms of the soil bacterium Bacillus subtilis, which develop wrinkles on their surfaces. Before the wrinkles form, discrete patches of cells in the biofilm die, laying down the wrinkling pattern, Süel and his colleagues reported online this week in the Proceedings of the National Academy of Sciences. Harnessing their new insight that overcrowding seems to lead to cell death, the researchers plated out cells in differ ent densities to form customized biofilms. More than fanciful, the technique may one day prove useful in tissue engineering and in making biofilms that produce useful chemicals.