So far so good For the moment, the gene genie is staying in its bottle
ONE of the most convincing arguments levelled against genetically modified crops is that the various genes in them that confer resistance to antibiotics will spread into the environment, eventually making life-threatening bacteria resistant to those drugs. But such doomsday scenarios look less convincing this week, as British researchers report having tried and failed to get various bacteria to take up such a gene from a commercial variety of GM maize.
John Heritage and his colleagues at the University of Leeds presented their results in Scarborough at a meeting of the British Society of Animal Science. The government-funded project is only halfway through and the researchers have yet to publish their results in full. But they have so far drawn a blank in experiments to see if bacteria pick up and activate bla, a gene in GM maize which confers resistance to ampicillin, a commonly used antibiotic. The researchers caution, however, that they still can't rule out the scenario altogether.
"It's encouraging that a reputable scientist has studied the transfer of a gene from GM maize to bacteria to gain actual data, rather than extending speculations that such an event might occur," says Charles Arntzen, president of the Boyce Thompson Institute for Plant Research in Ithaca, New York.
Developed by the Swiss company Ciba-Geigy, now Novartis, the maize is engineered to produce a bacterial toxin lethal to the European corn borer, a major pest of maize. Unlike other GM crops, it also contains the bla gene against ampicillin. The gene is not active in the plant, but the worry is that gut bacteria might pick it up and activate it when the maize is fed to animals.
Once in the environment, the bacteria might spread the same gene to hospitals, making life-threatening bugs resistant to ampicillin and to related penicillin-like antibiotics. Despite the fact that the bla gene is already abundant in bacteria through medical overuse of ampicillin, opponents of GM foods fear that the maize would exacerbate the existing problem.
Novartis sells the maize widely in the US, and in 1996 the European Commission cleared it for sale in Europe, despite opposition from British experts (New Scientist, 4 May 1996, p 7). But, two years later, France's highest court banned the sale and cultivation of the maize (New Scientist, 3 October 1998, p 5).
In his experiments, Heritage looked for evidence that gut bacteria from chickens had accepted and activated the bla gene, after the birds had been fed the GM maize for five days.
Heritage even served up the gene "on a plate" in plasmids, promiscuous loops of DNA routinely swapped by bacteria. He added pUC18, the bla-bearing plasmid used to produce the maize, to silage effluent and to saliva and rumen fluid taken from sheep. "We haven't seen it taken up and activated by bacteria in the normal flora of the rumen, saliva or silage yet," he says.
But these negative findings aren't the end of the story, Heritage warns. "That doesn't mean there aren't conditions where it might be taken up and activated." Next, he plans to test the fate of the bla gene when the maize is fed to sheep.
"I'm glad [the government] spent money investigating what was always a speculative scenario," says Derek Burke, former chair of the British committee that recommended Europe reject the maize. "It now looks as though the risk is less than was originally thought," he says.
Andy Coghlan
>From New Scientist magazine, 25 March 2000.