Question

Explain the mechanism of action for Bacillus Thuringiensis in Lepidotera species?

Answer 1

Bacillus thuringiensis is facultative anaerobe or aerobe and a sporulating bacteria. They are mostly found in insects, plants, soil, and aquatic environments. This bacteria show the presence of protein in crystal which is formed st sporulation time. The inclusion body that is a crystal includes the Cry protein that is encoded by gene Cry.

Mode of action of Bacillus Thuringiensis in lepidopterans species:
It occurs in 5 steps-
1. Ingestion of Bacillus Thuringiensis
2. Crystal solubilization
3. Protein activation
4. Protein receptor binding
5. Pore formation of membrane and lysis of cell

1. Ingestion of Bacillus Thuringiensis:
Bacillus Thuringiensis is ingested in the insect midgut.

2. Solubilization of crystal
Once the bacteria is ingested, the solubilization of crystal occur in the basic that is at pH between 9 to 12 environment of midgut. The pH of insect midgut is crucial as it will determine the action of cry toxin.

3. Protein activation
Now the enzyme protease will come into action and will release a protoxin after the toxin has been solubilized, and an active protein has been produced out.

4. Protein Receptor binding :
In the insect midgut, the inactivated protoxin by the action of digestive enzyme will get activated and thus will bind to the receptor present in microvilli found in lepidopterans gut. The specifity of Cry toxin is determined by the binding of apical microvilli to cry toxin.

5. Pore formation of membrane and lysis of cell.
By the Protein Receptor binding, now the toxin will abe able to pass the peritrophic membrane due to which pore is formed and cytoplasmic vacuolation occurs. Finally, leading to disruption cell. Thereby, microvilli is destroyed and insect is not able to feed leading to the death of an insect.