A US scientist has found a way to use bacteria to potentially store data on DVDs. Professor V Renugopalakrishnan of the Harvard Medical School has genetically modified a protein found in the membrane of a salt marsh microbe Halobacterium salinaru. The protein, bacteriorhodopsin, responds to light by storing energy from it for use by the microbe. When the protein is exposed to light it changes state; in fact it changes to a different molecule which then gradually, through a series of step changes, reverts to its original state.

The scientist has manipulated the DNA that produces the protein to prolong the light-changed state phase so that it lasts several years. The original state and the light-changed state can be binary one and zero.

A recording layer, containing bacteriorhodopsin, could be painted onto DVDs to provide a biological data recording facility. The individual protein molecules are only a few nanometres across, much smaller than the current recording areas on DVDs.

Professor V Renugopalakrishnan said: "The protein-based DVDs will be able to store at least 20 times more than the Blue-ray and eventually even up to 50,000 gigabytes (50TB) of information. You can pack literally thousands and thousands of those proteins on a media like a DVD, a CD or a film or whatever."

He thinks that such DVDs could replace current hard drives.

What we have here is a researcher with no current connection with the data storage industry. There is the germ of an idea - excuse the pun - but no method for applying the protein to a DVD or of reading or writing information. Lasers could be used for writing the information but possibly not for reading it.

Holographic technology is promising a 1.6TB DVD-sized disk. A 50TB disk sounds like a fantasy and any commercialisation of the concept will take years and years. It's interesting though and could be a pointer to what nanotechnology can do for storage.