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How does E. coli uptake oxygen? Most of the literature I found is concerned with response to oxygen level supplied in the medium, as opposed to how much is actually transported inside. Can they shut down the oxygen uptake if required? For example, to avoid damaging effects of reactive oxygen species.

There exist bacteria which die in presence of oxygen (strict anaerobe), while some use oxygen when available but also can survive in absence of it (facultative anaerobes, like E. coli). Are there bacteria which cannot consume oxygen for metabolism, but when exposed to oxygen they don't die, rather simply discard the oxygen and carry out fermentation? In a sense, they are strict anaerobe (their mode of metabolism is anaerobic), but they can still survive in presence of oxygen in environment.

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Have a look at this related post too –  WYSIWYG Oct 10 at 6:21

3 Answers 3

This question got me thinking about what are the metabolic enzymes that take oxygen up in E.coli. I searched the metacyc database for reactions that consume molecular oxygen and there are only 3 that take in oxygen and one that produces oxygen.

All three consumers of oxygen in E.coli are the oxidation of ubiquinone by at two sites in cytochrome-bcl or by cytochrome-bo. All of these export protons to create the gradient that drives ATP formation by F₀F₁ ATPase in the periplasm (the region between E.coli 's inner and outer membrane).

enter image description here

On the production side, superoxide dismutase reduces superoxide to oxygen to control oxidation damage. Apparently the innards of E.coli are somewhat oxygen tolerant.

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Thank you, is diffusion alone the mechanism of uptake? –  DurgaDatta Aug 21 at 11:00
    
yes, as @canadianer describes. I'd only wanted to add a description of how oxygen is taken into the system and consumed, which seemed like part of your question as well :) –  shigeta Aug 21 at 17:29
    
I would be grateful if you could provide me some references on how oxygen uptake capacity ( diffusion capacity) changes over growth rate or other variables, if any. –  DurgaDatta Aug 22 at 0:41

The plasma membrane is quite permeable to oxygen and thus oxygen enters the cell simply by diffusion. Reactive oxygen species can be reduced enzymatically in aerobic organisms. Obligate anaerobes lack or don't produce sufficient quantities of these enzymes. An organism that doesn't use oxygen for metabolism but is also not relatively harmed by it can be classified as aerotolerant.

enter image description here

Image from: http://en.m.wikipedia.org/wiki/Anaerobic_organism

Original Caption: Aerobic and anaerobic bacteria can be identified by growing them in test tubes of thioglycollate broth: 1: Obligate aerobes need oxygen because they cannot ferment or respire anaerobically. They gather at the top of the tube where the oxygen concentration is highest. 2: Obligate anaerobes are poisoned by oxygen, so they gather at the bottom of the tube where the oxygen concentration is lowest. 3: Facultative anaerobes can grow with or without oxygen because they can metabolise energy aerobically or anaerobically. They gather mostly at the top because aerobic respiration generates more ATP than either fermentation or anaerobic respiration. 4: Microaerophiles need oxygen because they cannot ferment or respire anaerobically. However, they are poisoned by high concentrations of oxygen. They gather in the upper part of the test tube but not the very top. 5: Aerotolerant organisms do not require oxygen as they metabolise energy anaerobically. Unlike obligate anaerobes however, they are not poisoned by oxygen. They can be found evenly spread throughout the test tube.

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Can you please give me an example of aerotolerant bacteria? –  DurgaDatta Aug 20 at 6:30
    
I think some Streptococcus and Lactobacillus spp. –  canadianer Aug 20 at 13:40
    
Clostridium intestinale has been described as aerotolerant. –  canadianer Aug 20 at 13:41
    
E. coli is a facultative anaerobe… –  canadianer Aug 20 at 16:39
    
I would like to get example of aerotolerant but strictly anaerobic bacteria. –  DurgaDatta Aug 21 at 10:58

I am adding a supplement/concluding remarks to the existing answers.

Some points to be considered:

  • Electron transport chain can work without oxygen and can use other chemical species as electron acceptors.
  • E.coli is capable of aerobic respiration, anaerobic (anoxic) respiration and fermentation (substrate level phosphorylation).

How does E. coli uptake oxygen?

Short answer as already mentioned by canadianer: Passive diffusion

Can they shut down the oxygen uptake if required?

Oxygen is the primary electron acceptor and E.coli would prefer oxygen to other electron acceptors. Only in the absence of oxygen is the FNR regulon switched on. Other bacteria can show negative aerotaxis i.e. running away from oxygen (they obviously have to be motile) [ref]. This paper also comments that positive and negative aerotaxis happens via a common mechanism- sensitivity of proton motive force to O₂. However, ROS has no role to play in it. It is most likely that at high oxygen levels E.coli will try to jack up anti-oxidant response. To conclude- they cannot regulate oxygen uptake.

Aerotolerant anaerobes: Clostridium perfringens, Clostridium intestinale.

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