Recently, I was sent counterfeit comments attributed to the Institute of Science in Society from an unsigned contribution to a pro industry discussion group which included the following remark. "We here at the Institute for [sic] Science in the Society, under the precautionary principle, call for an immediate ban on the use of Bt sprays in both conventional and organic agriculture."
The comments were based on my discussion on mating and gene transfer between Bacillus thuringiensis (Bt) and Bacillus anthracis (Ba) to exchange plasmids carrying toxin genes. These kinds of transfer are commonplace among prokaryotes in nature and they are based on mobilization (mob) genes. The two species of bacteria occupy rather different ecological niches that rarely overlap without human intervention. The fact that they can exchange genes is no reason to discourage the use of Bt bacteria in conventional and organic agriculture, provided that we avoid spraying Bt in locations known to have been sites where outbreaks of anthrax had decimated herds. Such sites are usually well-known to agricultural scientists and their locations are marked on maps available to the public. However, Bt has been used in aerial applications from helicopters in urban centers in British Columbia and in Washington State. And during those applications, little care was given to anthrax and former animal holding facilities. In future, it would be wise to ensure that Bt and Ba do not come into contact with each other by hazardous aerial spray programs.
Apart from the above considerations, accumulating evidence that bt-toxins are actual and potential allergens should make the protection of farm workers and sprayers a matter of primary concern . Similarly, care should be taken to avoid exposing the public to freshly sprayed produce.
Toxin genes from Bt or Ba may be introduced into other bacterial species as a further complication. For example The United States EPA approved encapsulated Bt http://www.epa.gov/pesticides/biopesticides/factsheets/fs006457e.htm, in this case Bt toxins genes were transferred to the soil bacterium Pseudomonas flourescens and the cultures were killed prior to their application as pesticides. The preparations are used a lot to deal with fruit insect pests. The preparations are more resistant to sunlight and have higher toxin content than commercial Bt sprays.
It is worth mentioning also that killed bacteria may participate in sex after death. Microbial necrophilia may result in transfer of both chromosomal and plasmid genes to appropriate recipients. Killed bacteria may protect the patented genes from being established in soil bacteria but some transfer of the genes to soil bacteria is likely to take place.
In conclusion, we should take the threat of bio-terrorism very seriously. Genetic engineering provides tools that can introduce hazardous genes into previously harmless microbes, either intentionally or otherwise, and we should be on our guard against those possibilities.
Article first published 24/10/01
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