AUSTRALIA鈥檚 biotechnology watchdog has rejected a plan to inoculate sheep and cattle with a genetically engineered bacterium. They fear that it could be transferred to other animals.
The modified bacterium is designed to protect livestock from a deadly poison in the leaves and seed pods of native trees. The Genetic Manipulation Advisory Committee objected to the plan because of worries that the bacterium might spread to mammalian pests, including goats, camels and rabbits, making them immune to the poison and encouraging their spread.
Large numbers of cattle and sheep in northern Australia die from fluoroacetate poisoning after eating certain native plants. Fluoroacetate is found in dozens of species from at least three genera of Australian trees, Acacia, Gastrolobium and Oxylobium. Livestock sometimes resort to eating native plants when pasture is poor, especially in dry periods. 鈥淭he poison acts like cyanide,鈥� says Keith Gregg, of the Institute of Biotechnology at the University of New England in Armidale, New South Wales. 鈥淚t doesn鈥檛 have a strong taste and the animals don鈥檛 learn to avoid it. Livestock is healthy one minute and dead the next.鈥�
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In one incident in western Queensland last year, 17 000 sheep from a flock of 70 000 died after eating toxic foliage. In another case in the Northern Territory, 1000 head of beef cattle from a herd of 3500 died. A decade ago, the Department of Primary Industries estimated that the average property owner lost A$140 000 (拢67 000) a year to the poison.
Eight years ago, forty owners of cattle and sheep stations in northern Australia clubbed together to finance research into the problem. Last year, Gregg and his team produced a genetically engineered bacterium that breaks down the poison before it has any effect.
Gregg鈥檚 group inserted a gene from a soil bacterium of the genus Moraxella into the bacterium Butyrivibrio fibrisolvens, which lives in the rumen of sheep and cattle. The gene from Moraxella produces an enzyme which detaches the fluorine atom from fluoroacetate, turning it into a harmless compound called glycolate.
The group planned to inoculate hundreds of animals from at least 30 stations in the Northern Territory and Queensland. The trial was designed to assess the effectiveness of the treatment and to show how well the bacterium spreads from animal to animal. While the bacterium survives only a few minutes outside the rumen, it passes from animal to animal in saliva, by licking or in droplets in the animal鈥檚 breath.
The GMAC said that if the organism was released, it would be capable of 鈥渨ide, irreversible dissemination鈥�. This is the first time the committee has turned down such a proposal.
Its main concern was the danger that the detoxifying gene might be transferred to other ruminants especially feral goats. These animals, descendants of goats brought to Australia by early settlers, are common in semiarid regions of New South Wales, Queensland, South Australia and Western Australia. They compete with native animals for food and shelter, and eat pasture grown for livestock. If the poison in native plants has prevented goats from reaching other parts of the country, the modified bacterium could help them spread there.
Before resubmitting their proposal, Gregg and his colleagues will look for any correlation between location of the trees and numbers of goats. 鈥淔rankly that is one possibility we hadn鈥檛 thought of,鈥� says Gregg.
They will also investigate the possibility of the gene spreading to rabbits and making them immune to the pesticide 1080, which contains fluoroacetate.
鈥淭he property owners were disappointed that the work could not proceed as planned, but they won鈥檛 let it drop,鈥� says Gregg. 鈥淲e were not surprised by what GMAC said. We were aware there were things we hadn鈥檛 covered. Now we know exactly what people are concerned about.鈥�
Gregg suggests that the committee鈥檚 rejection of his proposal shows that 鈥渢he system is working鈥�, and that this should reassure environmental groups. 鈥淚 cettainly wouldn鈥檛 want to live with the knowledge that I had created a bigger problem than the one I started with,鈥� he adds.