Bacillus thuringiensis is a Gram-positive, soil dwelling bacterium. Some strains of Bacillus thuringiensis produce proteins that kill certain insects. Bacillus thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein. The Bt toxin protein exists as inactive protoxins but once an insect ingest the inactive toxin, it is converted into an active form of toxin due to the alkaline pH of the gut which solubilizes the crystals. The activated toxin binds to the surface of midgut epithelial cells and creates pores that cause swelling and lysis and eventually cause death of the insect. The toxin is coded by a gene named cry. There are a number of them, for example, the proteins encoded by the genes cry I Ac and cry IIAb control the cotton bollworms, while the cry IAb controls corn borer. Thus, it is helpful in controlling the variety of insect pests. Through genetic engineering, scientists have introduced the gene responsible for making the Bt toxin into a range of crops. Hence, Bacillus thuringiensis is considered suitable for developing G.M. plants.

Because bacillus thuringiensis has the ability to divide at faster rate so by removing infection causing capacity it can be used to transfer and multiply many copies of desirable gene to form GM plants.