Heterotrophs and Carbon Fixation
October 29, 2008 at 7:01 pm #10345ElersongParticipant
So, I was reviewing some old notes concerning microbial metabolism, and I came up on a problem. In some of my notes, I have it written that heterotrophs use pre-fixed carbon in the form of organics to meet their need of a carbon source because they cannot fix their own carbon. In other notes, however, I have it written that heterotrophs simply cannot use only carbon dioxode as their carbon source and therefore use organics as a supplement.
My core inquiry is this: It is rather obvious that heterotrophs use organics in order to obtain carbon, but is it also possible for them to make use of carbon dioxide in order to obtain carbon as a supplement to that obtained through organics?
October 31, 2008 at 1:35 pm #86858
Yup, it’s possible.
The example can be seen in industrial fermentation of citric acid by Aspergillus niger. In order to produce citric acid, the CO2 produced from pyruvate decarboxylation is re-used again by combining it with another pyruvate to produce oxaloacetate (by the action of pyruvate carboxylase and PEP-carboxykinase enzymes).
At this stage, we obtain 2 equivalent of oxaloacetate where both of them are combined with acetyl-CoA yielding 2 citrate where one of them are released out of the cell.
In this example, we can see that the CO2 is re-used again. But it’s not obtained directly from air CO2 like the plant does.
Hope this helps,
November 1, 2008 at 3:22 pm #86873MrMisteryParticipant
That’s kind of interesting.
But in that case is the organism still called a heterotroph? Isn’t it a mixotroph?
November 2, 2008 at 11:23 pm #86900ElersongParticipant
That is interesting.
So I guess a better way to ask my question is this: If a heterotroph can behave in a manner in which it obtains carbon from both organics and CO2, then what is the criteria that differentiates mixotrophs from heterotrophs?
November 4, 2008 at 1:56 pm #86940
Well I can say it’s still called as heterotrophs (chemoorgano heterotrophs), because in order to generate those CO2, they still need organic molecules as the sole electron donor.
And I can say that mixotrophs are organisms which do not belong to these 4 nutrition types:
– Photolyto autotrophs
– Photoorgano heterotrophs
– Chemolyto autotrophs
– Chemoorgano heterotrophs
So if you found a microorganism which in example use a redox chemistry as a basis of energy yielding (chemo), using an inorganic electron donor like Fe2+ (lyto), but fixing organic compund also from an organic precursor (heterotroph), then I guess it’s classified into mixotroph.
November 5, 2008 at 2:23 am #86964MrMisteryParticipant
mixotroph is also an organism that can fit into more than one category. The most famous example is Euglena who is both a photolytoautotroph and a heterotroph
November 5, 2008 at 2:25 pm #86978
Yeah, that thing is Plantanimal 😆
November 6, 2008 at 9:18 am #87000
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