Research in synthetic biology—a combination of biology and engineering that builds artificial biological systems for research—has produced E. coli that have “color vision.” Using genetically engineered E. coli, different genes perform different biological functions depending upon the color of light—red, blue or green—to which they are exposed. The MIT team that produced this smart E. coli envision applications in commercial, pharmaceutical, and other applications.

The MIT system can be thought of as a computer chip. It is programmed with proteins and enzymes thatResearchers produced colored images on culture plates. Credit: Felix Moser/MIT process the light input and produce a biological output, the different bacterial responses to the different colors of light. The “chip” has a sensor array that reacts to the light, a circuit that processes the signal, and a resource allocator that actuates the desired response. The actuator is a critical component; it can shut the system down when necessary.

MIT professor of biological engineering Chris Voigt, co-author of a paper in Nature describing the technology, suggests thinking of the bacteria as marionettes. “Using different colors, we can control different genes that are being expressed,” he says.

In 2005, Voight developed a “bacterial camera” that produced black-and-white images. Five years ago, he made a camera with red and green images. The new three-color system required much more complex architecture. According to Voight, the complexity of the system increased exponentially with the addition of the third sensor. This required the addition of a “not” gate to prevent expression of unwanted color responses.

Voight and his team demonstrated their three-color camera by producing an image of the MIT logo and various other patterns, including a fruit still life. The images use a petri dish of genetically identical bacteria as “film.” Red, blue, and green light is aimed through a stencil at the top of the bacterial incubator.

One potential application of these light-reactive bacteria is as control mechanisms for industrial fermentation processes. The bacteria could easily be turned on and off, to stop or start the process. Current technology requires the addition of chemicals to fermentation vats, which is both expensive and time-consuming.

Another possibility is using bacteria to assemble materials. Other MIT researchers have started programming cells to assemble into living materials, which one day could become diagnostic sensors or solar cells.