Bacteria Bacillus thuringiensis forms protein crystals (Cry) during a particular phase of their growth. These crystals contain a toxic insecticidal protein. But this toxin does not kill the Bacillus (bacterium), because Bt toxin protein exists as inactive protoxins but once an insect digests the inactive toxin, it is converted into its active form due to the alkaline pH of the gut which solubilises the crystals.
