Aerobic And Anaerobic Growth

Question 1

Define Obligate aerobes.

Answer 1

Like humans, these organisms have an absolute requirement for oxygen.
Because aerobic metabolism generates the toxic byproduct, hydrogen peroxide, most obligate aerobes produce the enzyme catalase, which breaks down hydrogen peroxide to water and oxygen. Members of the genus pseudomonas’s are examples of this.

Question 2

Define Obligate anaerobes.

Answer 2

These organisms not only don’t require oxygen, but are killed or inhibited by its presence.
Because anaerobic metabolism does not generate hydrogen peroxide, obligate anaerobes, generally do not produce catalase. The bacterium that causes botulism, Clostridium botulinum, is an example.

Question 3

Define Facultative anaerobe.

Answer 3

These organisms will use oxygen for respiration, if if it’s available, but can also go without oxygen by fermenting. Again, since aerobic metabolism, generates hydrogen peroxide, these organisms typically produce catalase . E. Coli is an example of this.

Question 4

In addition to the three basic categories for microorganism classification in respect to oxygen requirements, there are two more. What are they?

Answer 4

1. Microaerophiles: organisms that require oxygen, but can only tolerate it in limited amounts.
2. Aerotolerant anaerobes: organisms that grow in the presence of oxygen, but don’t use it further metabolism.

Question 5

Define what an agar shake tube is.

Answer 5

Simply, an agar deep that has been boiled to drive off all dissolved gas before inoculating it and allowing it to solidify.

Question 6

Why do we want the tube to be de-gassed for aerobic and anaerobic growth?

Answer 6

Because since it has been degassed, oxygen will only be present where it has diffused back into the top surface of the agar, while the majority of the two remains anoxic.