Researchers have developed what is being dubbed as a biological “tape” recorder. By engineering bacteria the team was able to make the organisms record certain environmental events in their DNA, even figuring out a way to make them “time-stamp” them, allowing scientists not only to work out what, but also when something occurred.

“Such bacteria, swallowed by a patient, might be able to record the changes they experience through the whole digestive tract, yielding an unprecedented view of previously inaccessible phenomena,” explained Columbia University Medical Center’s Harris Wang, a senior author of this latest work published in Science.

The development is based on hijacking the bacteria’s own immune system, specifically the CRISPR-Cas complex. This is the same system that has revolutionized genetic editing in the past decade, as it takes snippets of DNA from whichever virus the bacterium encounters, and precisely inserts them into its own genome in chronological order.

This means that if that bacterium, or the strain to which it belongs, was to come across the same virus at some point in the future, it effectively has a library that it can reference, and can tell the immune system how best to tackle it. While other teams have figured out how to co-opt this in order to insert desired genes into everything from yeast to humans, the group behind this latest research instead saw promise in its ability to work a bit like a memory.

“When you think about recording temporally changing signals with electronics, or an audio recording... that’s a very powerful technology, but we were thinking how can you scale this to living cells themselves?” said graduate student Ravi Sheth, a co-author of the paper.

The team was able to modify the little circles of DNA found in bacteria, called plasmids, to record the time and events. They edited one to make copies of itself when it detected certain outside stimuli, like particular metabolites produced by specific bacteria, while a separate plasmid marked the time by continually adding spacers into its genome. This means that when the bacterium has been exposed to the correct stimuli, the signal will disrupt the time-keeping spacer signal, and denote when this took place.

So far the experiments have shown that the modified bacteria can record at least three different external signals while keeping track of the time for days on end. The hope is that this can be further refined to work within the human body or even to record pollutants in the environment.