Nitrogen-fixing cyanobacteria as gene delivery system for expressing mosquitocidal toxins of Bacillus thuringiensis ssp. israelensis

Classical biological control is the most successfuland promising way to replace chemical pesticides. Thesubspecies israelensis of Bacillusthuringiensis (Bti) is a safe and efficient agent tocontrol mosquito larvae and hence mosquito-bornediseases. One approach to overcome the low efficacyand short half-life in nature of current formulationsof Bti is by expressing the toxin genes in recombinantcyanobacteria as a delivery system. Attempts toexpress Bti toxin in cyanoabcteria have been carriedout during the last ten years. Toxicities of thetransgenic strains were however very low, even underregulation of strong promoters, too low to beeffective in vivo. Two Bti Cry proteins haverecently been co-expressed in the filamentousnitrogen-fixing cyanobacterium Anabaena PCC7120, resulting in clones with the highest toxicitiesand stabilities ever reached so far. However, toobtain a long-lasting preparation, it would be usefulto express Bti toxin genes in cyanobacterial strainsisolated from nature. This approach requiresdevelopment of a system for effective transformationinto such strains. Releasing such recombinant strainsto open environments is still a major obstacle inexploiting this biotechnology.