First, scientists identify a strain of Bt that kills the targeted insect. Then they isolate the gene that produces the lethal protein. That gene is removed from the Bt bacterium, and a gene conferring resistance to a chemical (usually antibiotic or herbicide) is attached that will prove useful in a later step.
The Bt gene with the resistance gene attached is inserted into plant cells. At this point, scientists must determine which plant cells have successfully received the Bt gene and are now transformed. Any plant cell that has the Bt gene must also have the resistance gene that was attached to it. Researchers grow the plant cells in the presence of the antibiotic or herbicide and select the plant cells that are unaffected by it. These genetically transformed plant cells are then grown into whole plants by a process called tissue culture. The modified plants produce the same lethal Bt protein produced by Bt bacteria because the plants now have the same gene.
Research to transfer insect resistance genes from Bt to crop plants is well under way. Corn, cotton and potatoes are three of the many commercial crops targeted for Bt insect resistance.