Bacillus thuringiensis spore and protein crystals Protein crystals made by strains of Bacillus thuringiensis are toxic to certain insects and have been put to use as a biopesticide. Rosemary Walsh, BACILLUS THURINGIENSIS. Courtesy of EMF-LSC, Penn State. Related Links Online Textbook: Genetically Modified Organisms: Introduction Related Terms: Bt Recombinant DNA Transgenic organism Related Images: Sporulating Bacillus thuringiensis cell Related Animations: Recombinant DNA View QuickTime Movie