facultative anaerobe?

Question

Assume you inocluated 100 facultatively anaerobic cells onto a nutrient agar and incubated the plate aerobically. You then inoculated 100 cells of the same species onto nutrient agar and incubated the second plant anaerobically. After incubation for 24 hours, you should have:
A. more colonies on the aerobic plate
B. more colonies on the anaerobic plate
C. the same number of colonies on both plates

the answer is C but i don't know why. I would think its A.

Answer 1

the aerobic sample would have colonies sooner, depending on the species. however, if you use something like E. coli which is perfectly content to grow anaerobically, you would get the same number of colonies either way. I've grown it anaerobically, it's fine. Some bacteria might be able to grow in oxygen but might not have the full compliment of the proper protective proteins and you would actually get more colonies and faster colonies anaerobically because they're less stressed than the cells in oxygen. Other bacteria might grow very slowly in the absence of oxygen, in which case you'd cell colonies much sooner aerobically.

Also, don't assume that because something lacks oxygen that it is HAS to be slower than aerobes in any way shape or form. One of the fastest dividing bacteria on record is C. perfringens, which can divide once every 10 minutes in the right conditions, and it's an obligate anaerobe.

Answer 2

The purpose of this question is to distinguish the difference between a "facultative" anaerobe and an "obligate" anaerobe. An obligate anaerobe requires the absence of oxygen, while the facultative can live with or without oxygen. Therefore, just as many facultative would grow on either plate. If the anaerobes were obligate, then they would only grow on the anaerobic plate.

Answer 3

Bad question. I think what they mean is that each of the 100 cells will divide and provide a colony, that is all the 100 cells had to live and multiply. They would be aerobes but they can tolerate an anaerobic enviromnent so.

Answer 4

Well, the cells are already anaerobic, correct? So exposing them to air would do nothing because they don't need it in the first place. The answer is in the problem.

Answer 5

Perhaps part of your thinking A is the correct understanding that whatever can use oxygen grows faster. This is correct - alot faster.
But the innoculation left viable cells in a supportive environment in either case. If you were checking every few hours you might have noticed the aerobic colonies first.

;-)

Answer 6

Just goes to show, no matter how you do it , as long as you DID incubate, you end up with "colonies".OR they are very invasive, assuming that is.