Engineering Bacillus thuringiensis bioinsecticides with an indigenous site-specific recombination system.

The cry genes of Bacillus thuringiensis encode a diverse group of crystal-forming proteins that exhibit insecticidal activity, particularly against the larvae of lepidopteran, coleopteran, and dipteran insects. The efficacy of B. thuringiensis-based biopesticides may be improved through the genetic manipulation of these genes. A gene transfer system has been developed for the introduction and maintenance of cloned insecticidal cry genes on small plasmids in B. thuringiensis. This vector system combines a B. thuringiensis plasmid replicon and an indigenous site-specific recombination system that allows for the selective removal of ancillary or foreign DNA from the recombinant bacterium after introduction of the Cry-encoding plasmid. The site-specific recombination system is useful for engineering strains with unique combinations of cry genes, resulting in new active ingredients with improved insecticidal properties.