Some strains of Bacillus thuringiensis produce proteins that kill certain insects like lepidopterans and coleopterans, etc. Bacillus thuringiensis forms some protein crystals. These crystals contain a toxic insecticidal protein. Bt toxin proteins exist as inactive protoxins, but once an insect ingests the inactive toxin it is converted to active form of toxin due to the alkaline $\mathrm{pH}$ of the alimentary canal that solublizes the crystals.