Images of the Virgin Mary have appeared on grilled cheese sandwiches, trees and now in a petri dish. But that last appearance was no heavenly manifestation. It was a sign that Christopher Voigt’s photographic bacteria were working.This summer, his team at the University of California at San Francisco injected light-sensing and communication genes from various bacterial species into Escherichia coli. Then he projected an image (anything from a circle to Alfred Hitchcock’s profile) onto a plate of the bacteria. Each cell senses if it’s in the light, and those in the dark secrete a chemical. The illuminated bacteria next to the shadowed cells detect that cue and turn black, creating a line-drawing copy.
Next, Voigt’s team will add color-sensing genes to E. coli so the bugs can make color images, a more complex step toward programming microorganisms to carry out useful jobs that require interpreting signals to make decisions. With the right combination of genes, scientists might one day be able to teach yeast to craft the perfect wine, or create “smart bacteria” that can be guided to kill cancer cells in the bloodstream, or instruct human cells to self-assemble into organs. “We don’t care how biology works normally,” Voigt says. “We want to get it to do unnatural things for us.”