(Redirected from Aerobic organisms)
Aerobic and anaerobic bacteria can be identified by growing them in a liquid culture:
1: Obligate aerobic bacteria gather at the top of the test tube in order to absorb maximal amount of oxygen.
2: Obligate anaerobic bacteria gather at the bottom to avoid oxygen.
3: Facultative bacteria gather mostly at the top, since aerobic respiration ist the most beneficial one; but as lack of oxygen does not hurt them, they can be found all along the test tube.
4: Microaerophiles gather at the upper part of the test tube but not at the top. They require oxygen but at a low concentration.
5: Aerotolerant bacteria are not affected at all by oxygen, and they are evenly spread along the test tube.
An 'aerobic organism' or ''aerobe'' is an
organism that has an
oxygen based
metabolism. Aerobes, in a process known as
cellular respiration, use oxygen to
oxidize substrates (for example
sugars and
fats) in order to obtain
energy.
★ 'Obligate aerobes' require oxygen for aerobic cellular respiration.
★ 'Facultative aerobes' can use oxygen, but also have
anaerobic methods of energy production.
★ '
Microaerophiles' are organisms that may use oxygen, but only at low concentrations.
★ 'Aerotolerant' organisms can survive in the presence of oxygen, but they are
anaerobic because they do not use it as a
terminal electron acceptor.
A good example would be the oxidation of
glucose (a
monosaccharide) in
aerobic respiration.
:C
6H
12O
6 + 6 O
2 + 38
ADP + 38 phosphate → 6 CO
2 + 6 H
2O + 38
ATP
The energy released in this equation is about 2880
kJ per mol, which is conserved in regenerating 38 ATP from 38 ADP per glucose. This is a factor of 19 times more energy per sugar molecule than the typical anaerobic reaction generates. Eukaryotic organisms (everything but bacteria) only get a net gain of 36 ATP regenerated from ADP in this process, due to an additional membrane that must be crossed by active transport.
Notice that oxygen is used during the oxidation of glucose and
water is produced.
This equation is a summary of what actually happens in three series of biochemical reactions:
glycolysis, the
Krebs cycle, and
oxidative phosphorylation.
Almost all
animals, most
fungi, and several
bacteria are obligate aerobes. Most
anaerobic organisms are bacteria. Being an obligate aerobe, although being advantageous from the energetical point of view, means also obligatory facing high levels of
oxidative stress.
Yeast is an example of a facultative aerobe. Individual human
cells are also facultative aerobes: they switch to
lactic acid fermentation if oxygen is not available. However, for the whole organism this cannot be sustained for long, and humans are therefore obligate aerobes.
Examples of Obligate Aerobic Bacteria: ''
Nocardia'' (
Gram-positive), ''
Pseudomonas aeruginosa'' (
Gram-negative), ''
Mycobacterium tuberculosis'' (
acid-fast), and ''
Bacillus'' (Gram-positive).
See also
★
Aerobic digestion
★
Anaerobic digestion
★
Facultative anaerobic organism
★
Fermentation (biochemistry)
★
Microaerophile
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