With the help of the emerging science of synthetic biology, students at UCSF and the University of Texas at Austin have created the first-ever photographs on agar populated with bacteria, instead of regular photo paper. The work, published in the journal Nature, was produced for MIT’s intercollegiate Genetically Engineered Machine (iGEM) competition. UCSF press office describes how this synthetic biology project was achieved, quoting Chris Voigt, PhD, an assistant professor of pharmaceutical chemistry at UCSF:
The new field focuses on identifying genes that control key traits, and then engineering microbes to activate the genes in novel combinations to create useful tools for medicine and technology.
“Essentially, we engineer the bug to give it new capabilities by combining different gene-based skills that it or other organisms already have.”
Like pixels on a computer screen switching between white and black, each bacterium either produced black pigment or didn’t, based on whether it was growing in a dark place or a light place in the dish. The resulting images are a collection of all the bacteria responding to the pattern of light.
E. coli live in the dark confines of the human gut and wouldn’t normally sense light, so the students had to engineer the unicellular machines to work as a photo-capturing surface. Levskaya and Voigt first engineered the bacteria to sense light by adding a light receptor protein from a photosynthetic blue-green alga to the E. coli cell surface. The microbe’s metabolism was modified to produce a chemical that gave the protein sensor the ability to see light in its new microbial host.
The light sensor was also genetically modified so that light turns off a gene that ultimately controls the production of a colored compound.
To create the actual photographs, the Texas students optimized pigments and growth media, and used a unique light projector largely designed and built by Aaron Chevalier, a physics undergraduate. They added a chemical compound to the agar, so that those bacteria that are in the dark produce black pigment and those that are in the light do not.
The device projects the pattern of light, such as an image of a person, onto the dish of bacteria growing at body temperature in an incubator. After about 12 to 15 hours of exposure (the time it takes for a bacterial population to grow and fill up the petri dish), the light projector is removed.
What’s left is a permanent living photograph.
The bacterial photograph could allow material to be printed with incredibly high precision, Voigt said.
“We estimate that the resolution of these photographs is about 100 megapixels, or about 10 times better than high-resolution printers. The difference is that we can print gene expression.”