thuringiensis

Bacillus thuringiensis, commonly known as Bt, is a Gram-positive, spore-forming bacterium found in soils and on plant surfaces. During sporulation it produces protein crystals that contain insecticidal toxins. The organism was first described in 1901 by Shigetane Ishiwata after an outbreak in silkworms, and was named Bacillus thuringiensis by Ernst Berliner in 1915, after the Thuringia region of Germany where the isolate came from.

Bt's insecticidal properties are conferred by crystalline delta-endotoxins, typically encoded on plasmids and grouped by their host range into Cry and Cyt toxins. Cry toxins are highly specific to certain insect orders; Cry1 family targets Lepidoptera, Cry3 to some beetles, while Cyt toxins often act synergistically or against Diptera. The toxins become active in the insect gut after proteolytic processing and cause cell lysis, leading to death.

Applications and impact: Bt is used as a microbial insecticide in agriculture, with formulations such as sprays and granules, and is a key component of organic farming due to its specificity and low non-target risk. Strains and formulations include Bacillus thuringiensis kurstaki for lepidopteran pests and israelensis for mosquito and blackfly larvae. Bt genes have also been introduced into crops (for example, Bt corn and Bt cotton) to produce endogenous insecticidal Cry toxins, reducing the need for chemical pesticides.

Safety and regulation: Bt products are generally regarded as safe for humans and most wildlife, with approvals in many countries. Risks to non-target organisms exist mainly for aquatic invertebrates in Bt israelensis applications, and over-reliance can drive pest resistance, prompting integrated pest management strategies.