- Bacillus thuringiensis (Bt) is a Gram-positive, spore-forming bacterium found naturally in soil and on plant surfaces.
- It is best known for its ability to produce insecticidal proteins during sporulation, making it one of the most important biological agents in pest control. These proteins, called Cry (crystal) proteins or δ-endotoxins, form crystalline inclusions that are toxic to specific groups of insects but harmless to humans, animals, and most non-target organisms. Because of this highly selective toxicity, B. thuringiensis has become a cornerstone of both traditional biopesticides and modern transgenic crop development.
- The insecticidal activity of B. thuringiensis was first observed in the early 20th century, when it was found to cause disease in silkworm larvae. Since then, Bt-based products have been widely used in agriculture as microbial insecticides. When susceptible insects ingest Bt spores or Cry proteins, the proteins are solubilized in the alkaline environment of the insect midgut and activated by gut proteases. The activated toxin binds to receptors on the intestinal lining, forming pores in the gut membrane. This disrupts ion balance, causes gut paralysis, and ultimately kills the insect. Importantly, the mode of action is highly specific, targeting only insects with the appropriate gut receptors, which explains why Bt is considered environmentally safe.
- Beyond its role as a microbial pesticide, Bacillus thuringiensis has been pivotal in the development of transgenic crops. By introducing Cry protein genes into plants, scientists created insect-resistant varieties such as Bt corn, Bt cotton, and Bt eggplant. These crops produce the insecticidal proteins directly in their tissues, protecting them from major pests like the European corn borer, cotton bollworm, and fruit borer. The adoption of Bt crops worldwide has significantly reduced the need for chemical insecticides, lowering production costs for farmers, reducing environmental pollution, and promoting more sustainable agriculture.
- The use of B. thuringiensis has also advanced research in biotechnology and microbial ecology. Different strains of the bacterium produce a wide variety of Cry proteins, each with unique insecticidal specificity. This diversity has allowed for the development of biopesticides targeted at various insect orders, including Lepidoptera (moths and butterflies), Coleoptera (beetles), and Diptera (mosquitoes). In addition, other proteins produced by Bt, such as Cyt toxins and Vip (vegetative insecticidal proteins), expand its insecticidal spectrum and provide new tools for pest control.
- Despite its many advantages, the widespread use of Bt-based pesticides and transgenic crops has raised concerns about resistance development. Over time, some insect populations have evolved resistance to specific Cry proteins, threatening the long-term effectiveness of Bt technology. To mitigate this risk, strategies such as gene pyramiding (stacking multiple toxin genes in a single crop) and refuge planting (maintaining non-Bt crop zones to support susceptible insect populations) have been implemented. These approaches help slow resistance development and preserve the efficacy of Bt crops.
