59) A microbiology instructor prepares cultures for a...

59) A microbiology instructor prepares cultures for a gram-staining practical laboratory by inoculating growth medium with a gram-positive coccus (nonmotile) and a gram-negative rod (motile). The goal is to demonstrate staining of a mixed culture. The flask is incubated at 35 °C for 24 hours without aeration. A sample is stained and reveals only gram-negative rods. Both cultures are known facultative anaerobes. Give a likely reason for success of the gram-negative rod. Assume that the cultures have comparable intrinsic growth rates.

I put this as my answer but the professor said it was wrong:

My answer:   I believe that the success of the gram-negative rod was because there was a more proper electron acceptor and the organism was able to use to perform anaerobic respiration better than the gram-positive. The aerobic organisms grow only in presence of oxygen. The anaerobic organisms strictly grow only in lack of oxygen and any traces of oxygen are also harmful to them. The facultative anaerobes can survive in presence of oxygen but can better grow in absence of oxygen.

 

She said: You are not correct on 59. The answer is actually included in the question.