Supporters of growth promoters will point to the lack of cases in the field of cross infection or gene transfer.

BBC: Animals and antibiotics: the risks

Gene transfer is an age-old concern of farmers, who've learned how to prevent pollen cross-contamination when necessary for commercial reasons.

FORBES: Food Fight

The Tennessee team is now working with food crops as well as tobacco, and to extend its studies on gene transfer.

BBC: NEWS | Science/Nature | Scientists hope to ease GM fears

"This discovery represents a significant advance because it avoids the need for cross-kingdom gene transfer, " he said, noting that many other scientists are working towards the total removal of selection markers.

BBC: NEWS | Science/Nature | Scientists hope to ease GM fears

The dominant patent holder in agrobacterium transformation, the most widely-used means of plant gene-transfer, is Monsanto, a big agricultural firm.

ECONOMIST: Can open source revolutionise biotech?

They used a modified version of the HIV virus to transfer a gene for neprilysin to neurons of genetically modified mice which produced human beta-amyloid.

BBC: Alzheimer's gene treatment hope