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Biopesticide and Bioweapons
by Joseph Cummins, Department of Plant Sciences,
University of Western Ontario
Bacillus anthracis, the cause of anthrax poisoning, is currently a great concern because of its employment as a terror weapon. Bacillus thuringiensis is both a major pesticide and the source of the genes used to produce insect toxins in GM crops. A third bacterium, Bacillus cereus, is a common soil bacterium and a common cause of food poisoning. The three species of bacteria are closely related, differing mainly in their plasmids (plasmids are circular DNA molecules that replicate independently of the chromosome). The plasmids of the three species may readily be transferred from one species to another (1). The toxin genes from the three species are located on the plasmids and the genes tend to cluster in “islands” that sometimes are mobilized by viruses that integrate themselves into the plasmid as prophage. The ready exchange of plasmids bearing toxin genes between the three species has raised some concern (2).
The virulence of B. anthracis depends on the presence of two large plasmids; strains lacking one or the other plasmid are not virulent. Plasmid X02 carries genes that make polymers of glutamic acid (1 of 20 amino acids that make proteins). These glutamic acid polymers go on the cell surface to inhibit phagocytes, cells in the body that engulf and take in bacteria and digest them. Plasmid X01 carries the three toxin genes coding for edema factor, lethal factor and protective antigen (3).
…it is not unlikely that GM crops carrying anthrax genes could be produced…
The endotoxins of B. thuringiensis (bt toxins) are stored as inactive crystals in bacterial spores, which create pores on the cells of the insect gut, causing an inrush of water that bursts the cell. In the event that B. anthracis were to transfer plasmids to B. thuringiensis, recombination could create plasmids bearing toxins both for anthrax and for killing insects. New strains of B. anthracis with unpredictable properties could arise.
The bt toxin genes are employed in crop genetic engineering. Currently, there has been little or no effort to evaluate the possible recombination between B. anthracis in the field and the endotoxin genes of crop plants.
Such gene exchange could occur in the soil between GM plant debris and bacteria.
Also, it is not unlikely that GM crops carrying anthrax genes could be produced either for vaccines or for bio-weapons.
There is an extensive history of the use of biowarfare agents, and in recent years, bioterrorism has been a growing concern. An extensive biological warfare program in Iraq was discovered after the Gulf War of 1991. Revelations concerning the covert program in the former Soviet Union also attracted much public attention. The Rajneeshee Cult, an Indian religious group, contaminated restaurant salad bars in Oregon in 1984 with Salmonella typhimurium, and about 751 citizens were infected. The cult’s motivation was to incapacitate voters in order to win a local election and to seize political control of Dallas and Wasco counties. Larry Wayne Harris wanted to alert Americans to the Iraqi biological warfare threat and sought a separate homeland for whites in the United States. Harris made vague threats against US federal officials on behalf of right-wing “patriot” groups. He obtained the B. anthracis vaccine strain and Yersinia pestis (plague bacteria), and reportedly several other bacteria, and discussed the dissemination of biological warfare agents by means of crop duster aircraft and other methods. Harris was arrested in 1998 after he made threatening remarks to US officials and talked openly about biological warfare terrorism (4).
Developments in biotechnology make it possible to greatly amplify the impact of traditional biowarfare agents.
Notes 1. Helgason E, AndreasOkstadt O, Caugant D, Johannsen H, Fouet A, Mock M, Hegna I, and Kolsto A. Bacillus anthracis, Bacillus cereus and Bacillus thuringiensis: One species on the basis of genetic evidence. Applied and Enviromental Microbiology 2000, 66, 2627-30.
2. Bouchie A. Bacillus identity crisis. Nature Biotech 2000, 18, 813.
3. Okinaka R, Cloud K, Hampton O, et al. Sequence and organization of X01, the large Bacillus anthracis plasmid harbouring the anthrax toxin genes. J Bacteriol 1999, 181, 6509-15.
4. Hawley R and Eitzen M. Biological weapons: a primer for microbiologists. Ann Rev. Microbiol 2001, 55, 235-53.
This October 23, 2001 ISIS Report is available at the I-SIS website: http://www.i-sis.org/