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8 January 2003

Data stored in multiplying bacteria

A message encoded as artificial DNA can be stored within the genomes of multiplying bacteria and then accurately retrieved, US scientists have shown.

Their concern that all current ways of storing information, from paper to electronic memory, can easily be lost or destroyed prompted them to devise a new type of memory – within living organisms.

“A big concern is the protection of valuable information in the case of a nuclear catastrophe,” says information technologist Pak Chung Wong, of the Pacific Northwest National Laboratory in Washington State. The laboratory was set up as a nuclear energy research institute.

A similar catastrophe strikes the US in the cult television series Dark Angel, in which a colossal electromagnetic pulse wipes out the electronic infrastructure. “Bacteria may be an inexpensive and stable long-term means of data storage,” Wong told New Scientist.


Small world

The scientists took the words of the song It’s a Small World and translated it into a code based on the four “letters” of DNA. They then created artificial DNA strands recording different parts of the song. These DNA messages, each about 150 bases long, were inserted into bacteria such as E. coli and Deinococcus radiodurans.

The latter is especially good at surviving extreme conditions, says Wong. It can tolerate high temperatures, desiccation, ultraviolet light and ionising radiation doses 1000 times higher than would be fatal to humans.

The beginning and end of each inserted message have special DNA tags devised by the scientists. These “sentinels” stop the bacteria from identifying the message as an invading a virus and destroying it, says Wong.

“The magic of the sentinel is that it protects the information, so that even after a hundred bacterial generations we were able to retrieve the exact message,” says Wong. “Once the DNA message is in bacteria, it is protected and can survive.” And as a millilitre of liquid can contain up to billion bacteria, the potential capacity of such a memory system is enormous.

Spontaneous mutations

Deinococcus is adapted to survive in extreme conditions and is consequently very good at repairing any mutations that spontaneously arise in its DNA code. But Huw Williams, a bacteriologist at Imperial College, London, says that the small size of the inserted messages makes it no surprise that they survive 100 generations intact.

Williams thinks a greater danger than mutations changing the message is that they could make some bugs better adapted to their environment than others. So far, Wong and colleagues have kept the different message colonies separate, but in future they aim to retrieve messages from a mixed colony.

“If you grow the colonies indefinitely, less well-adapted bacteria may be lost over time,” he says. “The question is whether you will be able to retain all your message populations. But this is intriguing work and very forward looking.”