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Lecture 15

MBIO 1010 Lecture 15: Lecture 15

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University of Manitoba
MBIO 1010
Christopher Rathgeber

Microbiology 1010 – Lecture Notes Oxygen and Microbial Growth  Obligate aerobes – Require oxygen to live Strict anaerobes – Do not require oxygen and may even be killed by exposure   Facultative aerobes – Can live with or without oxygen, they use oxygen when it is available Aerotolerant anaerobes – Can tolerate oxygen and grow in its presence even though they cannot use it  Microaerophiles – Can use oxygen only when it is present at levels reduced from that in air We need oxygen because it’s an effective (positive) that it pulls e- down the ETC and promotes the release of high levels of energy. If not protective measures against the dangerous forms of O2 – then you will die! Oxygen and Microbial Growth (Continued…) Differences in oxygen use/tolerance can be distinguished using thioglycolate broth: o  Complex medium that separates microbes based on oxygen requirements Thioglycolate reacts with oxygen, so oxygen can penetrate only the top of the tube.  Also contains an oxygen responsive dye that turns pink in the presence of oxygen and colourless when the oxygen is low or absent. Obligate aerobe – grows only in the oxic zone at the top of the tube Strict anaerobe – grows only in the anoxic zone at the bottom of the tube Facultative anaerobe – grows throughout the tube But better growth occurs in the oxic zone, where it can generate energy by aerobic respiration.  Microaerophile – grows in a narrow band between the oxic and anoxic zones It needs O 2for aerobic respiration  But it can’t grow too close to the top because it is killed by atmospheric O 2levels  Aerotolerant anaerobe – grows well throughout the tube  Doesn’t use O 2 And it’s not harmed by O 2 84 Microbiology 1010 – Lecture Notes Thioglycolate = makes sure the o2 can only stay towards the top of the tube The dye = give you the stripe to know where the oxygen is within the tube. Oxygen and Microbial Growth (Continued…) Special techniques are needed to grow anaerobic microbes  Reducing agents – chemicals that may be added to culture media to reduce oxygen  (e.g., thioglycolate, cysteine, 2S and other sulphur containing compounds) Removal of air, and replacement with an inert gas (nitrogen or argon) If the doctor thinks you have anaerobe – located in an abcess within the body – he must drain it. Put petri dish inside and the air on the top is removed – take away atmospheric O2 Nitrogen and argon are put in and you literally take out O2 and put in nitrogen or argon only. They are really smelly – anaerobic. 85 Microbiology 1010 – Lecture Notes Oxygen and Microbial Growth (Continued…) Several toxic forms of oxygen can be formed spontaneously in the cell  : o Superoxide anion o Hydrogen peroxide o Hydroxyl radical Hydroxyl radical = Unpaired election that is desperately looking to pair itself off. Molecule of oxygen carrying full unit of negativity = superoxide Hydroxyl radical - It gives rise to reaction oxygen species ….. Species that has an election withou
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