Oxygen tolerance and toxicity Flashcards
What is an oxic/aerobic environment?
An environment that contains any amount of O2
What is an anoxic/anaerobic environment?
No O2 in the environment whatsoever
What is an aerobe?
An organism that can use O2 as TEA in aerobic respiration
What is an obligate aerobe?
An organism that can only do aerobic respiration and nothing else, so requires O2 at all time
How common are obligate aerobes? Where are they found?
Relatively rare. Having no backup isn’t the best plan. They’re found in areas where the oxygen source is constantly replenished, like our upper respiratory tract
How do you culture obligate aerobes?
The culture needs to be constantly shaken or aerated
What are facultative anaerobes?
Organisms that can use and tolerate oxygen, and will preferentially use it if its there. But they switch to another pathway if its not there and do perfectly fine without it
Where how common are facultative anaerobes? Where are they found?
Super common, found just about everywhere
How do you culture facultative anaerobes?
However you want
What are microaerophiles?
Organisms that require O2 for metabolism, but only very small amounts because they have enzymes that get destroyed by O2
Where how common are microaerophiles? Where are they found?
Pretty rare, can only live in a very narrow range of O2 concentrations. Found in our stomachs
How do you culture microaerophiles?
Candle jar
What is an anaerobe?
An organism that lacks the machinery needed to use aerobic respiration
What are aerotolerant anaerobes?
Organisms that only use fermentation and don’t care if O2 is there or not
What are obligate anaerobes?
Organisms that are poisoned by O2 and must live in an oxygen free environment
Where how common are obligate anaerobes? Where are they found?
Surprisingly common. Found in places like our colons and in the centre of biofilms
How do you culture obligate anaerobes?
Have to be in a special cabinet with no oxygen. Hard to culture
How do you test for oxygen tolerance?
Grow the bacteria in a liquid culture without mixing and look where the growth is
Where does an obligate aerobe grow in an unmixed liquid culture tube?
Only at the top
Where does a facultative anaerobe grow in an unmixed liquid culture tube?
Everywhere, but especially dense at the top
Where does an obligate anaerobe grow in an unmixed liquid culture tube?
Only at the bottom
Where does an aerotolerant anaerobe grow in an unmixed liquid culture tube?
Everywhere equally
Where does a microaerophile grow in an unmixed liquid culture tube?
Right below the oxic zone
How can oxygen be dangerous to cells?
ROS are byproducts of aerobic metabolism
What are 3 ROS that need to be dealt with?
Superoxide, hydrogen peroxide, hydroxyl radicals
How do macrophages use ROS to kill bacteria?
They engulf bacteria and put them in a phagosome. The phagosome fuses with a lysosome, then reactions take place in the phagosome that create ROS to kill the bacteria
How do bacteria detoxify ROS?
Aerobes and aerotolerant bacteria produce enzymes that will detoxify ROS
What are the 3 enzymes that detoxify ROS?
Superoxide dimutase, catalase, peroxidase
What does superoxide dimutase do?
Converts superoxides to O2 and H2O2
Is superoxide dimutase found in all aerobes?
Yes
What are the two enzymes that detoxify hydrogen peroxide?
Catalase and peroxidase
What does catalase do?
Converts H2O2 to O2 and H2O
Is catalase found in all aerobes?
No, only found in some
What does peroxidase do?
Converts H2O2 and NADH to water and NAD+
How do you tell if a bacteria has catalase or peroxidase?
Catalase test. You place a drop of H2O2 on the bacteria and look for bubbles. If they do bubble, they have catalase. If they don’t they have peroxidase
Is there an enzyme to get rid of hydroxyl radicals?
No. If the other enzymes are working hydroxyl radicals will never be produced
