Ex. 10: Oxygen Requirements

Question 1

What is aerotolerance?

Answer 1

the ability/inability of organism to grow in presence of oxygen

Question 2

What is obligate aerobes?

Answer 2

micro-orgranisms that grow only in presence of oxygen

Question 3

What is facultative anaerobes?

Answer 3

grow better in presence of oxygen but will still grow in absence

Question 4

What is strict anaerobes?

Answer 4

grow only in absence of oxygen, harmed by its presence

Question 5

How are toxic oxygen products produced?

Answer 5

oxygen has two unpaired electrons and is easily reduced

Question 6

Name two toxic oxygen product

Answer 6

superoxide radicals (O2) and hydrogen peroxide (H2O2)

Question 7

Why are h202 and superoxide radicals toxic?

Answer 7

they oxidize cellular components making them nonfunctional

Question 8

What enzymes do obligate aerobes and facultative anearobes contain?

Answer 8

superoxide dismutase (SOD) and catalase

Question 9

What do the enzymes in obligate aerobes and facultative anaerobes do?

Answer 9

SOD and catalase catalyze the destruction of superoxide radicals and h202, respectively

Question 10

What are aerotolerant anaerobes?

Answer 10

micro-organisms that cannot use O2 but are not harmed by it

Question 11

What are microaerophiles?

Answer 11

organisms requiring small amount of O2 and increased CO2 for growth, are inhibited by O2 at normal atmospheric levels

Question 12

How do solid growth media allow for visual determination of aerotolerane?

Answer 12

contains oxygen gradient, shows O2’s tendency to populate areas where conditions are favourable

Question 13

How is oxygen gradient formed?

Answer 13

liquefied agar is cooled to room temperature. O2 diffuses back as agar solidifies, creating gradient of oxygen concentrations

Question 14

What is the gradient of oxygen concentrations?

Answer 14

aerobic at the top to anaerobic at the bottom

Question 15

What is an agar shake culture?

Answer 15

bacteria inoculated into tube of liquefied agar (deep) and mixed to distribute before solidifying

Question 16

Why is agar shake culture used?

Answer 16

acts as good visual indicator of oxygen tolerance in micro-organisms

Question 17

What are two methods used when culturing anaerobes?

Answer 17

free oxygen excluded from environment or reducing media is used

Question 18

What apparatus is used to excluding oxygen from environment?

Answer 18

GasPak (BBL) anaerobic system aka Brewer anaerobic jar

Question 19

What is methane blue strip indicate?

Answer 19

redox potential indicator that is blue in presence of O2, white when reduced

Question 20

What are reducing media?

Answer 20

media that contains reagents chemically combined with free oxygen, reduce concentration of oxygen

Question 21

Why is a small amount of agar added in reducing medium?

Answer 21

increase viscosity, which reduced diffusion of air into medium

Question 22

What does Fluid Thioglycollate Medium combine with?

Answer 22

oxygen

Question 23

Why is Reazurine used in reducing medium?

Answer 23

redox potential indicator, turning pink when oxidized and colourless when reduced

Question 24

What does oxidized mean?

Answer 24

in the presence of excess oxygen

Question 25

When is a candle jar used?

Answer 25

when culturing microaerophiles on petri plates with non reducing medium

Question 26

What are the usual levels of gases in the air?

Answer 26

21% O2, and 0.3% CO2

Question 27

What are the usual levels of gases in candle jar?

Answer 27

16% O2, and 4% CO2

Question 28

What happens in the presence of palladium catalyst?

Answer 28

hydrogen will react with oxygen forming water. removes free oxygen from jar

Question 29

Cultures are placed in anaerobic jar with envelope containing what?

Answer 29

chemicals that release hydrogen and carbon dioxide when exposed to air

Question 30

Why does the lid of catalyst chamber warm as reaction goes?

Answer 30

water droplets form on inside walls of anaerobic jar