Bacillus thuringiensis
பேசில்லஸ் துரிஞ்சியென்சிஸ்
Nature does not use chemical pesticides; it uses biological warfare. Bacillus thuringiensis is not just a bacterium; it is a precision-guided weapon. If you confuse the inactive protoxin with the active toxin, you lose marks. Focus.
The idea
Bacillus thuringiensis (Bt) produces insecticidal protein crystals during a specific phase of its growth. These crystals contain a toxic insecticidal protein. When an insect larva ingests the inactive protoxin, the alkaline pH of the gut solubilizes it into the active toxin. This active toxin binds to the surface of midgut epithelial cells, creating pores that cause cell swelling and lysis, eventually killing the larva.
Why it matters
It exists as a highly specific natural defense mechanism against certain insect larvae, allowing for targeted pest control without harming beneficial insects.
NEET lens
NEET focuses on the activation mechanism: alkaline pH is the key. Remember, the toxin is inactive in the bacterium but active in the insect gut. Questions often test the specific target: butterfly caterpillars. Do not confuse this with Bt cotton technology; keep the biological principle distinct from the transgenic application.
Clinical significance
In an ecosystem, Bt acts as a highly specific biocontrol agent, preventing the collapse of crop yields without harming non-target beneficial insects like pollinators. Failure to utilize such biological controls leads to excessive chemical pesticide accumulation, which enters the human food chain and causes bioaccumulation and biomagnification.
Introduction
Bacillus thuringiensis (Bt) is a soil bacterium used as a microbial biocontrol agent against butterfly caterpillars; its toxin genes are also used to make Bt crops.
Core concept
Use as a biocontrol agent (NCERT): dried spores of Bt are mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees, where they are eaten by insect larvae. In the gut of the larvae, the toxin is released and the larvae get killed. The bacterial disease kills the caterpillars but leaves other insects unharmed. Through genetic engineering, B. thuringiensis toxin genes have been introduced into plants such as Bt cotton, making the plants resistant to attack by insect pests. Bt forms protein crystals containing a toxic insecticidal protein during a particular phase of its growth; the toxin exists as an inactive protoxin and becomes active in the alkaline pH of the insect gut.
Go deeper
Bt does not kill the bacterium itself because the toxin is in an inactive protoxin form within the bacterium. Specific cry genes target specific insects: cryIAc and cryIIAb control cotton bollworms; cryIAb controls corn borer.
From Class 10
Some bacteria produce poisons that kill specific insect pests — farmers can spray them instead of chemical pesticides.