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The cry proteins of Bacillus thuringiensis become active toxins only after being ingested by an insect. What activates them in the insect gut?

  • A Acidic pH of the insect gut directly dissolves the protective protein crystals over time
  • B Alkaline pH of the insect gut along with gut proteases dissolve the crystals
  • C Insect digestive enzymes acting at a neutral gut pH alone, independent of pH level
  • D High temperature within the insect gut directly denatures the protective outer coat

Correct answer: B. Alkaline pH of the insect gut along with gut proteases dissolve the crystals

Explanation: The alkaline pH of the insect midgut, combined with gut proteases, dissolves the crystalline inclusions and activates the pro-toxin cry proteins into active toxins that bind to midgut epithelial cells, causing cell lysis and death.

Concept context

Microorganisms in food, medicine, sewage treatment, biocontrol, and biofertilizers

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