Imagine an experiment in which the nitrogen-fixing capacity of a nitrogen-fixing bacterium is selectively knocked out (all other functions remain intact). This knockout strain is then placed in competition with an unaltered bacterium (the control) under two circumstances: one in which ammonia and other sources of fixed nitrogen are abundant, and one in which these sources are limiting (only N₂is readily available). Assume that the nitrogen-fixing capacity in the control is present all the time (not regulated). Which of the following would be the most likely result? A) The knockout strain would outcompete the control strain in the abundant condition and lose to the control strain in the limiting condition. B) The knockout strain would outcompete the control strain in the abundant condition and be competitively equal to the control strain in the limiting condition. C) The knockout strain would outcompete the control strain in both conditions. D) The knockout strain would outcompete the control strain in the limiting condition and be competitively equal in the abundant condition. E) The knockout strain would outcompete the control strain in the limiting condition and lose to the control strain in the abundant condition.

Question

Quizplus · Accepted Answer

In the abundant condition, the knockout strain would not need to fix nitrogen, giving it a competitive advantage as it doesn't expend energy on nitrogen fixation. In the limiting condition, the control strain would have the advantage as it can fix nitrogen, which the knockout strain cannot do.

Imagine an Experiment in Which the Nitrogen-Fixing Capacity of a Nitrogen-Fixing