Oxygen

Question 1

Describe the difference between aerobes and anaerobes.

Answer 1

○Aerobes are organisms that can grow in oxygen while anaerobe are organisms that can grow without oxygen (Willey, et al., 2011, pp.163-181).

References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.

Question 2

What are the toxic effects of oxygen?

Answer 2

○Oxygen can be harmful as it has unpaired electrons in its outer shell, which makes it unstable (Willey, et al., 2011, pp.163-181).
○Oxygen reduction can form reactive oxygen species (ROS), which are toxic oxygen derivatives, including hydrogen peroxide, the superoxide radical and the hydroxyl radical (Willey, et al., 2011, pp.163-181).
○ROS can damage lipids, proteins and nucleic acids (Willey, et al., 2011, pp.163-181).

References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.

Question 2

Describe four ways in which anaerobes may be cultured.

Answer 2

○To culture anaerobes, the media must exclude all oxygen (Willey, et al., 2011, pp.163-181).
○One way to remove all oxygen is to boil anaerobic media which contain reducing agents, like thioglycollate or cysteine (Willey, et al., 2011, pp.163-181).
○This removes all oxygen, and reducing agents ensure there are no residual dissolved oxygen left (Willey, et al., 2011, pp.163-181).

○Oxygen can be removed from an anaerobic chamber by using a vacuum pump to remove air and pump in nitrogen gas (Willey, et al., 2011, pp.163-181).
○Then pump in a gas mix containing hydrogen, which reacts with any remaining oxygen in presence of a palladium catalyst to form water (Willey, et al., 2011, pp.163-181).

○Another way to culture small quantities of anaerobes is by using GasPak jars (Willey, et al., 2011, pp.163-181.
These contain hydrogen and a palladium catalyst which eliminate oxygen (Willey, et al., 2011, pp.163-181).

○Another way is using plastic bags which contain calcium carbonate and a catalyst, which removes oxygen and creates an anoxic environment rich in CO2 (Willey, et al., 2011, pp.163-181).

References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.

Question 3

Describe obligate aerobes.

Answer 3

○Obligate aerobes need oxygen for growth, and cannot grow in absence of oxygen (Willey, et al., 2011, pp.163-181).

References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.

Question 4

Define microaerophiles.

Answer 4

○Microaerophiles need oxygen for growth, but only at low levels of 2-10%, and are damaged by the normal atmospheric level of oxygen (Willey, et al., 2011, pp.163-181).

References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.

Question 5

Define facultative anaerobes.

Answer 5

○Facultative anaerobes are microbes that don’t need oxygen to grow but grow better with oxygen available (Willey, et al., 2011, pp.163-181).

References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.

Question 6

Define aerotolerant anaerobes.

Answer 6

○Aerotolerant anaerobes are able to grow well with or without oxygen (Willey, et al., 2011, pp.163-181).

References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.

Question 7

Define obligate anaerobes.

Answer 7

○Obligate anaerobes cannot grow with oxygen present and can only grow if it isn’t available (Willey, et al., 2011, pp.163-181).

References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.

Question 8

How do aerobes and other oxygen-tolerant microbes protect themselves from the toxic effects of oxygen?

Answer 8

○Enzymes can be used to protect microbe from toxic oxygen products (Willey, et al., 2011, pp.163-181).
○Superoxide dismutase (SOD) used by obligate aerobes and facultative anaerobes to destroy superoxide radical, by converting superoxide radical to oxygen and hydrogen peroxide (Willey, et al., 2011, pp.163-181).
○They also use catalase and peroxidase to destroy hydrogen peroxide, by converting hydrogen peroxide to water and oxygen (Willey, et al., 2011, pp.163-181).
○Aerotolerant anaerobes use SOD instead of catalase (Willey, et al., 2011, pp.163-181).
○Microaerophiles use superoxide reductase, which reduces superoxide radical to hydrogen peroxide without producing oxygen, and peroxidase, which converts the hydrogen peroxide to water (Willey, et al., 2011, pp.163-181).
○As obligate anaerobes don’t contain any enzymes to protect themselves from toxic oxygen products, they cannot tolerate oxygen (Willey, et al., 2011, pp.163-181).

References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.