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$Bacillus\ thuringiensis$ forms protein crystals which contain insecticidal protein. This protein
A
Is activated by acid pH of the foregut of the insect pest
B
Does not kill the carrier bacterium which is itself resistant to this toxin
C
Binds with epithelial cells of midgut of the insect pest ultimately killing it
D
Is coded by several genes including the gene $cry$
Detailed Solution
The Bt toxin protein exists in the bacterium as an inactive protoxin (crystals).
When an insect ingests it, the crystals are solubilised by the alkaline pH of the gut and the protoxin is converted into the active toxin. So it is activated by alkaline, not acid, pH.
The activated toxin binds to the surface of the midgut epithelial cells and creates pores, which cause the cells to swell and lyse, eventually killing the insect.
The bacterium is not killed because the protein is inactive inside it, not because the bacterium is resistant to the toxin.
The toxin is coded by a gene named $cry$ (different cry genes such as cryIAc, cryIIAb, cryIAb code for different toxins), not by 'several genes including cry'.
Hence the protein binds with epithelial cells of the midgut of the insect pest, ultimately killing it.
When an insect ingests it, the crystals are solubilised by the alkaline pH of the gut and the protoxin is converted into the active toxin. So it is activated by alkaline, not acid, pH.
The activated toxin binds to the surface of the midgut epithelial cells and creates pores, which cause the cells to swell and lyse, eventually killing the insect.
The bacterium is not killed because the protein is inactive inside it, not because the bacterium is resistant to the toxin.
The toxin is coded by a gene named $cry$ (different cry genes such as cryIAc, cryIIAb, cryIAb code for different toxins), not by 'several genes including cry'.
Hence the protein binds with epithelial cells of the midgut of the insect pest, ultimately killing it.