Bacillus thuringiensis (or Bt) is a Gram-positive, soil-dwelling bacterium, commonly used as a biological pesticide. B. thuringiensis also occurs naturally in the gut of caterpillars of various types of moths and butterflies, as well on leaf surfaces, aquatic environments, animal feces, insect-rich environments, and flour mills and grain-storage facilities.
During sporulation, many Bt strains produce crystal proteins (proteinaceous inclusions), called δ-endotoxins, that have insecticidal action. This has led to their use as insecticides, and more recently to genetically modified crops using Bt genes. Many crystal-producing Bt strains, though, do not have insecticidal properties.
Bacillus thuringiensis (Bt) is a bacteria that produces proteins which are toxic to insects. Bt’s extreme toxicity comes as no surprise. It’s in the same family of bacteria as B. anthracis, which causes anthrax, and B. cereus, which causes food poisoning.
Bt is toxic to many of the insects that can disrupt a farming operation. It’s widely used as a biological pesticide and, in fact, Bt is the most widely used biological pesticide in the world. Bt application can happen one of two ways — Bt can be sprayed on crops or it can be added to the DNA of genetically modified crops. Neither method is positive for health or society, but the second is quite interesting in that it actually embeds a self-contained pesticide within the crop. If a bug eats corn that contains Bt, the bug dies — simple. In the United States, Bt use is widely used on corn, cotton, and potatoes, among other crops, and it’s been pushed as a less dangerous alternative to harsh chemical pesticides.
Exposure to Bt is a major problem for agricultural workers who handle chemicals that contain Bt. In a study that evaluated greenhouse workers, it was found that nearly half had Bt in their fecal samples. One of the biggest problems with occupational Bt exposure is that, despite causing serious lung damage, it does not irritate the airway when it’s inhaled. It’s been reported that many people who are subject to occupational exposure do not wear protective masks.

In a purified form, some of the proteins produced by Bt are acutely toxic to mammals. However, in their natural form, acute toxicity of commonly-used Bt varieties is limited to caterpillars, mosquito larvae, and beetle larvae. Bt is closely related to B. cereus, a bacteria that causes food poisoning and to B. anthracis, the agent of the disease anthrax. Few studies have been conducted on the chronic health effects, carcinogenicity, or mutagenicity of Bt. People exposed to Bt have complained of respiratory, eye, and skin irritation, and one corneal ulcer has occurred after direct contact with a Bt formulation. People also suffer from allergies to the ingredients. People with compromised immune systems may be particularly susceptible to Bt. Bt is less toxic to mammals and shows fewer environmental effects than many synthetic insecticides. Its environmental and health effects as well as those of all other alternatives must be thoroughly considered before use. Bt should be used only when necessary, and in the smallest quantities possible. It should always be used as part of a sustainable management program.

Author: Divya Vashishth