Let's see...for my hypothesis, I wrote that the enzymes work best in the temperatures at which the bacteria was found, and designed an experiment with the bacteria working with the substrate at 10 degrees, 20, 30, etc...all the way to 90, and said to measure the amount of gas produced at each stage.
I thought it was a pretty decent attempt, considering my mind was a total blank for 5 minutes after reading the question.
[Edit: 90, not 50 you idiot.]