Internet users have a variety of formats in which to store their movies, and biologists have now joined the party. Researchers have used the microbial immune system called CRISPR–Cas to encode a movie in the genome of the bacterium Escherichia coli.

The technical achievement, reported on 12 July in Nature[1], is a step towards creating cellular recording systems capable of encoding a series of events, says Seth Shipman, a synthetic biologist at Harvard Medical School in Boston, Massachusetts. While studying brain development, Shipman became frustrated because no available technique could capture what caused one cell to take on a different identity than another. This inspired him to try out cellular encoding.

“Cells have this privileged access to all sorts of information,” he says. “I would like to have these molecular recordings functioning in the developing nervous system and recording information.”

To develop such a system, however, would require his team to establish a method for recording hundreds of events in the cell. Shipman and his colleagues, including geneticist George Church, harnessed the CRISPR–Cas immune system best known for enabling researchers to alter genomes with relative ease and accuracy.

This system employs an enzyme called Cas9, which can be directed to make cuts at specific sites in the genome. Shipman’s team, however, exploited a different feature of the system: its ability to capture snippets of DNA from invading viruses and store them in an organized array in the genome. In nature, those snippets then target Cas9 to slice up the invader’s DNA.

In Shipman’s system, the snippets instead corresponded to pixels in an image. The researchers encoded the shading of each pixel, along with a barcode to indicate its position in the image, into 33 DNA letters. Each frame of the movie consisted of 104 of these DNA fragments.

Credit: Seth Shipman

Moving pictures

The movie that the researchers selected consisted of five frames adapted from British photographer Eadweard Muybridge’s Human and Animal Locomotion series. The photos capture a mare named Annie G. galloping in 1887.

The team introduced the DNA into the bacteria at a rate of one frame per day for five days. They then sequenced the CRISPR regions in a population of bacteria to recover the image. Because the CRISPR system adds DNA snippets sequentially, the position of each snippet in the array could be used to determine the original frame to which the snippet belonged.

The system is a long way from becoming the recorder that Shipman dreamt of while studying the brain. But Victor Zhirnov, chief scientist at the Semiconductor Research Corporation in Durham, North Carolina, calls the work “revolutionary,” and thinks that the ability to store information in living cells could ultimately overcome some of the storage problems associated with DNA, such as the relative slowness and difficulty of reading and writing the information.

Other CRISPR-Cas systems can convert RNA into DNA that is then inserted into the CRISPR array, notes bioengineer Randall Platt at the Swiss Federal Institute of Technology in Basel. This could open up the door to using the arrays to track gene expression.

Getting to that point will take substantial technological advances, he adds. The information is stored in populations of cells, rather than individual cells. And no one has yet transferred the CRISPR arrays into mammalian cells. “It’s full of limitations, but this is pioneering work that they’re doing,” he says. “It’s elegant.”

Zhirnov hopes to start tinkering with the technique at his research foundation. “It’s like this is the first airplane flown in 1930: it was just a curiosity,” says Zhirnov. “But ten years from that, we had airplanes almost like what we have today.”