The following is the first two paragraphs from an article by Deborah McKenzie called Friend or foe in New Scientist October 9, 1999 p. 22
'Friendly' bacteria make terrific insecticides. But just a few genes separate the good guys from the bad.
Give or take a few mobile bits of DNA, the bacteria bacillus thuringiensis (Bt), B. Cereus and B. anthracis are all the same species, biologists believe. If your are thinking 'so what', then consider this: Bt is sprayed over crops in large quantities and B. anthracis is the bug that causes anthrax.
Small genetic differences have so far maintained that distinction that makes B. anthracis a notorious human pathogen and Bt merely a useful pest control bug. However, Bacillus expert Lars Andrup of the National Institute of Occupational Health in Copenhagen has identified a novel gene swapping system that enables Bt to exchange an unusually wide variety of DNA with other bacillus cells. The potential for spawning very dangerous strains and unleashing them into the environment is clearly there, he says.