Bacteriology 102: Catabolism and Oxygen Relationships
|Condensed from our catabolism and oxygen relationship pages.|
I. Purposes of Catabolism:
II. Regarding their source of reducing power, organisms can be classified as either organotrophs or lithotrophs:
III. Regarding their ultimate source of energy, organisms can be classified as either chemotrophs or phototrophs:
To make a long story short, we can use the example of a typical fermentation pathway (stepwise/sequential chain of chemical reactions) where glucose is oxidized to pyruvate (the oxidation stage of the pathway) and pyruvate is then reduced to fermentation products such as lactic acid (the reduction stage of the pathway). At a certain step in the oxidation stage where compound A loses electrons (which are picked up by co-enzyme NAD+), the electrons can be transferred to compound C in the reduction stage (thus "regenerating" the NAD+).
In the generation of ATP, the "P" (phosphate) can be "free" (inorganic) or attached to an intermediate compound in the pathway (organic). As this phosphate is transferred to ADP in the formation of ATP and does not incorporate energy associated with electron transport, the term "substrate-level phosphorylation" applies.
Phototrophy can be OXYGENIC (evolving O2 when H2O serves as the electron donor) or ANOXYGENIC (non-O2-evolving).
While fermenters (above) tend to be organotrophs, respirers can be organotrophs or lithotrophs. For respiration, we have O2 as an external electron acceptor, and the reduction stage seen in fermentation is replaced here by continued oxidation. An organic substrate can be oxidized completely to CO2 as O2 is reduced to H2O.
ANAEROBIC RESPIRATION employs an electron acceptor other than O2 such as nitrate (NO3–) which is reduced to nitrite (NO2–) or N2.
IV. An attempt to produce an abbreviated summary of catabolism based on the above follows.
V. Based on the above, we can characterize and classify bacteria consistently and comprehensively by applying the method(s) of energy generation of which an organism is capable:
How three of these processes are associated with anaerobic growth is shown here.
VI. Thioglycollate Medium – which we use in our Bacteriology laboratory courses – is a "standard" medium often used for the determination of oxygen relationships of bacteria.
|Corresponding tube no. above||1||2||3||4|
|Oxygen relationship designation||STRICT|
|Ability to grow anaerobically||–||+||+||+|
|Reaction in Glucose O/F Medium|
(for those able to grow well in medium)
|O or –||F|
|Response to sodium azide in a|
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