Bacillus thuringiensis is a soil bacterium that produces crystalline inclusions during sporulation, containing insecticidal proteins (delta-endotoxins) with high specificity against insects. These proteins are protoxins that are proteolytically converted into toxic fragments in the insect midgut, leading to cell lysis and larval death. The proteins are highly specific due to their interaction with high-affinity binding sites on the midgut epithelium. B. thuringiensis crystal proteins are used in plant protection as biological insecticides, with transgenic plants expressing these proteins showing resistance to insect pests. However, resistance development is a concern, and the use of different crystal protein genes can help expand the host range of B. thuringiensis strains. The cry genes are classified into different families based on their structure and insecticidal activity, with cryI genes being the most studied. These genes are located on large plasmids and can be transferred between strains. The expression of cry genes is regulated by specific promoters and sigma factors, and the proteins are toxic to various insect species. The mode of action involves the formation of pores in the midgut epithelium, leading to osmotic imbalance and cell lysis. The specificity of the proteins is determined by their interaction with specific receptors in the insect gut. The use of B. thuringiensis crystal proteins in transgenic plants has shown promise in protecting crops from insect damage, but further research is needed to address resistance and improve efficacy.Bacillus thuringiensis is a soil bacterium that produces crystalline inclusions during sporulation, containing insecticidal proteins (delta-endotoxins) with high specificity against insects. These proteins are protoxins that are proteolytically converted into toxic fragments in the insect midgut, leading to cell lysis and larval death. The proteins are highly specific due to their interaction with high-affinity binding sites on the midgut epithelium. B. thuringiensis crystal proteins are used in plant protection as biological insecticides, with transgenic plants expressing these proteins showing resistance to insect pests. However, resistance development is a concern, and the use of different crystal protein genes can help expand the host range of B. thuringiensis strains. The cry genes are classified into different families based on their structure and insecticidal activity, with cryI genes being the most studied. These genes are located on large plasmids and can be transferred between strains. The expression of cry genes is regulated by specific promoters and sigma factors, and the proteins are toxic to various insect species. The mode of action involves the formation of pores in the midgut epithelium, leading to osmotic imbalance and cell lysis. The specificity of the proteins is determined by their interaction with specific receptors in the insect gut. The use of B. thuringiensis crystal proteins in transgenic plants has shown promise in protecting crops from insect damage, but further research is needed to address resistance and improve efficacy.