Engineering Escherichia coli to see light

These smart bacteria ‘photograph’ a light pattern as a high-definition chemical image. Phytochromes are membrane-bound photoreceptors found in plants and some bacteria. There are none in Escherichia coli, but with the introduction of a genetic circuit that fuses a cyanobacterial photoreceptor to an intracellular kinase, E. coli sees the light. The bacteria then act as a photographic film, producing a chemical image when light is projected onto it. We have designed a bacterial system that is switched between different states by red light. The system consists of a synthetic sensor kinase that allows a lawn of bacteria to function as a biological film, such that the projection of a pattern of light on to the bacteria produces a high-definition (about 100 megapixels per square inch), two-dimensional chemical image. This spatial control of bacterial gene expression could be used to ‘print’ complex biological materials, for example, and to investigate signalling pathways through precise spatial and temporal control of their phosphorylation steps.