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Carboxydotrophs are organisms that use carbon monoxide (CO) as the energy source for their metabolism. The ability to derive energy from inorganic molecules ranks them among lithotrophs. Caroboxydotrophs are exclusively prokaryotic, including both bacteria and archaea. Their metabolic pathways start with carbon monoxide as the electron donor and oxidise it to carbon dioxide. This reaction can be carried out in the presence of molecular oxygen or a variety of other electron acceptors, such as water, sulfate and ferric iron, dividing carboxydotrophs into aerobic and anaerobic. Both groups can further be autotrophic or heterotrophic based on the inorganic or organic source of their carbon.

Heterotrophic carboxydotrophs use electrons from CO only for respiration that stores their energy in the form of adenosine triphosphate (ATP). Autotrophs additionally channel electrons into biosynthesis and fix carbon from inorganic CO or, placing them among primary producers. This is done by the reverse electron transport mechanism, driving electrons from inorganic sources through the electron transport chain in the opposite direction and expends previously conserved energy to produce NADH and NADPH. Other carboxydotrophs are photolithotrophic and start the transport chain with electrons excited from bacteriochlorophyll by the absorption of light and replace them with electrons derived from CO or other inorganic molecules other than water, avoiding the need to expend conserved energy.

Aerobic Carboxydotrophs
The sum of the reactions in aerobic oxidation of CO is the following:


 * 2 CO + O2 → 2 CO2 + energy

The pathway is similar to the knallgas reaction carried out by the hydrogen oxidizing bacteria.

Aerobic CODH
Carboxydotrophic reactions are enabled by the enzyme CO dehydrogenase (CODH)

Aerobic Carbon Fixation
Some carboxydotrophs can use the produced energy to fix using the Calvin–Benson–Bassham (CBB) cycle that is also used in the light-independent reactions of plant photosynthesis. Similarly, the enzyme catalysing the first step of this reaction is ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO).