Answer: Bacillus thuringiensis.
- A Rhizobium, a nitrogen-fixing root bacterium
- B Bacillus thuringiensis
- C Azotobacter, a free-living nitrogen fixer
- D Pseudomonas, a common soil bacterium
Correct answer: B. Bacillus thuringiensis
Explanation: Bacillus thuringiensis (Bt) produces cry proteins (delta endotoxins) that are toxic to caterpillars and other insect pests.
Sewage passes through physical removal (primary), then aerobic biological treatment where microbes form flocs that consume organic matter (secondary); the settled activated sludge is then digested anaerobically to produce biogas - a deliberate switch from aerobic to anaerobic conditions between stages.
Concept context
Microorganisms in food, medicine, sewage treatment, biocontrol, and biofertilizers