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Biopesticide and Bioweapons

Bacillus thuringiensis, used as biopesticide and Bacillus anthracis, the anthrax species involved in current bioweapons scare are related, Prof. Joe Cummins reports.

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 contain genetic origins of replication that allow them to 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 (caused to move) by lysogenic bacterial viruses (bacteriophages that integrate themselves into the bacterial genome or bacterial 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 (one of twenty 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].

The insect killing ability of B. thuringiensis is based on the presence of an island of toxin genes [4] on one of many (up to 17) plasmids in the bacterium [5]. The strain, B. thuringiensis serovar israelensis, has a plasmid-borne prophage that is induced to multiply when the strain mates with phage-insensitive strains of B. thuringiensis or B. cereus [6].

The endotoxins of B. thuringiensis (bt toxins) are stored as inactive crystals in bacterial spores, which are activated in the insect gut to create pores on the cells of the insect gut, causing an inrush of water that bursts the cell. In the event that B. anthracis mated 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 bio-warfare 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. He had links to Christian Identity and the Aryan Nation, a white supremacist group. 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 [7].

Developments in biotechnology makes it possible to greatly amplify the impact of traditional biowarfare agents and made the means to create bio-terror weapons available to a significant part of the population through training in genetic engineering.

Article first published 23/10/01



References

  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. "Bacillus identity crisis" By A. Bouchie, 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. BenDov E, Nissan G, Pelleg N, Manasherab R, Bousiba S and Zaritsky A. Refined circular restriction map of the Bacillus thuingiensis subspisrealensis plasmid carrying the mosquito larvicidal genes. Plasmid 1999, 42, 186-93
  5. Andrus L, Damgaard J, Wasserman K, Boe L, Madsen S, and Hansen F. Complete nucleotide sequence of the Bacillus thuringiensis subsp isrealensis plasmid pTX14-3 and its correlation with biological properties. Plasmid 1994, 72-88
  6. Kanda K, Takada Y, Kawasaki F, Kato F and Murata A.Mating in Bacillus thuringiensis can induce plasmid integrative prophage J7W-1. ActaVirol 2000, 44, 189-92
  7. Hawley R and Eitzen M. Biological weapons a primer for microbiologists. Ann Rev. Microbiol 2001, 55, 235-53.

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