Answer: Azotobacter uses high respiration rates and an alginate capsule to maintain low internal O2, while Rhizobium relies on leghaemoglobin (plant-produced) in nodules to buffer O2 supply to bacteroids.
- A Both of these soil bacteria are sometimes thought to rely on a largely identical molecular mechanism to shield their nitrogenase enzyme from oxygen damage in routine practice overall in most cases
- B Azotobacter uses high respiration rates and an alginate capsule to maintain low internal O2, while Rhizobium relies on leghaemoglobin (plant-produced) in nodules to buffer O2 supply to bacteroids
- C Mainly Rhizobium shows meaningful sensitivity to oxygen, while Azotobacter requires little protective mechanism by comparison under typical conditions according to standard textbooks in general practice
- D Azotobacter instead relies specifically on specialized heterocysts, while Rhizobium relies mainly on the outer nodule cortex layer for protection as frequently described in most textbook accounts
Correct answer: B. Azotobacter uses high respiration rates and an alginate capsule to maintain low internal O2, while Rhizobium relies on leghaemoglobin (plant-produced) in nodules to buffer O2 supply to bacteroids
Explanation: Both protect the oxygen-sensitive nitrogenase differently: Azotobacter uses very high respiration rates to consume O2 and produces an alginate capsule as an O2 barrier, while Rhizobium relies on leghaemoglobin produced by the host legume plant in nodules to carefully regulate O2 supply to bacteroids.
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