Normal human cells have been dried out and revived eight days later using a trick evolved by a bacterium that can survive for centuries without water. The technique could have a wide range of medical uses.
Blood for transfusions could be stored for long periods, for example, or carried to remote disasters without having to be kept cool. Antibodies and vaccines would have an almost unlimited shelf life, making them easier to distribute in developing countries.
Desiccated medical supplies could even be sent on long space missions. And it should become possible to make cell-based biosensors to detect poisons such as nerve gas.
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鈥淵ou could rehydrate them when you needed the sensor,鈥� says Malcolm Potts of the Virginia Tech Center for Genomics in Blacksburg, who developed the technique.
Witches butter
Our cells usually die within seconds without water. But Potts and his colleague David Helm knew of a photosynthetic bacterium, or cyanobacterium, called Nostoc commune, that can survive such harsh conditions.
N. commune lives on exposed rock surfaces, where it often dries out. When the rock gets wet again the cells come back to life, swelling up to form gel-like masses whose sudden appearances led to the popular names 鈥渟tar jelly鈥� and 鈥渨itches butter鈥�.
N. commune survives by surrounding itself with a slimy substance called glycan, Potts says. 鈥淚t forms a woolly overcoat for the cells.鈥� Glycan is thought to protect cell membranes, as well as slowing the rate of drying.
So Potts and Helm tried mixing purified glycan with human kidney cells and drying them out at room temperature. When they rehydrated the cells eight days later, half of the cells recovered and started dividing again, Potts told a meeting of Britain鈥檚 Society for Experimental Biology in Canterbury earlier this month.
鈥淚t鈥檚 a breakthrough,鈥� says Potts. 鈥淏y applying the techniques we have found in cyanobacteria, we can dry out human cells. It鈥檚 very exciting.鈥�
Freeze dry
Alan Tunnacliffe of the Institute of Biotechnology at Cambridge University says he鈥檚 surprised the cells survived with only glycan to protect them, as it does not get inside the cells. 鈥淚 am a little sceptical,鈥� he says. 鈥淏ut if it does work, it is a major achievement.鈥�
Last year, Fred Levine of the University of California in San Diego reported that he had revived dried human cells after 5 days (快猫短视频, 19 February 2000, p 11). But this technique doesn鈥檛 work for normal cells 鈥� Levine鈥檚 team had to genetically modify the cells to make a sugar called trehalose, which protects cells against freezing and drying from the inside.
Other researchers have failed to repeat Levine鈥檚 results. But he insists the technique works. 鈥淲e have been drying cells, putting them in a standard cardboard container, sending them [from California] to the East Coast and having them successfully rehydrated,鈥� he says.
Potts and Helm hope that one day tissues and perhaps even organs could be dried out and revived. But this won鈥檛 be achieved with glycan alone, Potts says. 鈥淚n the end it鈥檚 bound to require a combination of different approaches.鈥�