Bacillus thuringiensis (Bt) is a common bacteria that has played a very uncommon role in agriculture and the development of genetically modified foods. The natural insecticidal abilities of these bacteria have made them an important pest control tool for nearly a century. Protecting our food from pests has been an ongoing battle ever since humans began cultivating food. The U.S. Food and Agriculture Organization estimates that some 20-40% of global crop totals are lost annually due to disease and pests, and the Environmental Protection Agency estimates that around 5 billion pounds of pesticides are used globally each year, costing more than 35 billion dollars.[1]
Prior to 1996 dichloro-diphenyl-trichloroethane, or DDT, and similar synthetic chemical pesticides were used to control insect pests. Indiscriminate use of synthetic chemical insecticides led to the contamination of water and food sources, poisoning of non-target beneficial insects and development of insect-pests resistant to the chemical insecticides. The CDC also raised concerns as residues of these pesticides were found in meat, poultry, fish, plants and even breast milk. High doses of DDT can cause seizers, vomiting and tremors in humans.[2] Increased public concerns about the adverse environmental effects of indiscriminate use of chemical insecticides prompted a search of alternative methods for insect-pest control. One of the promising alternatives has been the use of biological control agents. There is well-documented history of safe application of Bt biopesticides. Only a few insecticidal sprays are required on Bt transgenic crops, which not only save cost and time, but also reduce health risks.[3]
Bt is a very common bacteria found in a variety of distinct environments, from soil, to dessert, to tundra. It was first isolated in 1901 by Japanese biologist Ishiwata Shigetane as he studied the causes of a disease afflicting silkworms. Then in 1911, the German scientist Ernst Berliner re-isolated Bt from flour moth caterpillars that had been collected from Thuringia, Germany. Soon Berliner determined that the Bt bacteria was specifically toxic to certain insect larva and not others. However, it wasn’t until 1928 that anyone attempted to harness Bt as a tool for pest control. Initially, the bacteria were used to fend off European corn borer, which historically has been a very damaging corn pest. This initiated the development of the first commercial Bt based biopesticide, Sporine, which was introduced in 1938 in France. Since then, Bt-based biopesticides have been a significant pest control strategy and are actually a common pest control strategy in organic agriculture. By the 1990s, tens of thousands of Bt strains had been isolated, with toxicity to a broad range of insect species.
Still, it was a game changer when the first GM corn engineered with genes from Bt became available in 1995. Since then, crops with Bt genes have come to dominate the majority of varieties planted in the U.S., representing 81% of total corn and 84% of total cotton acreage. 1
How does Bt work to protect against pests? The Bt bacteria produces a Cry protein that is toxic to larval insects. The Cry protein is a crystalline protein that reacts with gut enzymes specific to larval insects to destroy and lyse cells in the gut. This leads to starvation and death of the insect. By using biotechnology to insert the gene that codes for this protein the plant can essentially protect itself.
Bt crops are protected specifically against European corn borer, southwestern corn borer, tobacco budworm, cotton bollworm, pink bollworm and the Colorado potato beetle. These are some of the most damaging insects to agriculture. With the plants being able to protect themselves against these insects, less harmful pesticides are required to keep the plant healthy. This leads to less negative impact on the environment and human health.
Current crops available with Bt genetic technology include corn, sweet corn, soybeans, cotton, potato and canola. More research is being done on using common types of soil bacteria, yeasts and molds to allow plants to protect themselves against all manner of pests. This will ultimately lead to more robust crops and a healthier environment.
[1] Insecticidal Plants: The Tech and Safety of GM Bt Crops. M. Niederhuber. http://sitn.hms.harvard.edu/flash/2015/insecticidal-plants/. 2015.
[2] DDT FactSheet. CDC.org. 11.2009
[3] Bacillus thuringiensis (Bt) transgenic crop: an environment friendly insect-pest management strategy. J Environ Biol. 2008 Sep;29(5):641-53
[4] BT Crops. University of Malakand. M.Z.Arifeen. 10.2014