IT sounds like an environmentalist鈥檚 worst nightmare鈥攁 genetically engineered bacterium running amok in a nuclear wilderness. But researchers say it could be the best way to prevent toxic chemicals from leaking out of highly radioactive sites.
There are some 3000 sites where the US produced nuclear bombs, containing 70 million cubic metres of soil鈥攅nough to cover 10 000 soccer pitches to a depth of 1 metre. Some of these sites are contaminated with heavy metals and organic chemicals that can leach into groundwater, but many sites are so radioactive they are no-go zones.
Michael Daly and his colleagues at the Uniformed Services University of the Health Sciences in Bethesda, Maryland, hope to tackle the problem with Deinococcus radiodurans, a 鈥渟uperbug鈥� that can survive doses of radiation that will kill almost anything else (New 杏吧原创, 9 December 1995, p 18). Daly has identified genes in other bacteria which neutralise harmful metals or destroy organic compounds. One by one, he is stitching them into D. radiodurans so that it can clean up the nuclear sites.
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His latest triumph is to equip the superbug with a gene that detoxifies mercury and one that destroys organic solvents. One gene, borrowed from Escherichia coli, converts highly toxic mercury ions into metallic mercury vapour, which is less harmful. 鈥淚t would go into the atmosphere and be diluted over the surface of the Earth,鈥� he says. The other gene, from Pseudomonas, converts toluene and chlorobenzene into carbon dioxide and water.
Daly is working on other genes that prevent heavy metals from leaching into the water supply. 鈥淭he best you can hope for is to trap everything and stop it getting out, and then you just leave it there,鈥� he says.