Life forms that use carbon dioxide as
the sole or principal carbon source for growth are described as autotrophs,
and the use of carbon dioxide is called autotrophic carbon dioxide fixation.
In the reticulo-rumen the autotrophs are the methanogens and the homoacetogens
and both of these groups of microorganisms use the acetyl CoA pathway of
CO2 fixation. These, and other autotrophs that live in the dark,
(and who do not carry out photosynthesis) may also be called chemoautotrophs
just to make that point (organisms that carry out photosynthesis are phototrophs
and most are autotrophic, hence the descriptor photoautotrohic). The term
chemolithoautotrophy can also be applied to the methanogens and the homoacetogens.
The "litho" component of the name conveys the idea that they derive reducing
equivalents (for reductive biosynthesis and for ATP generation) from the
oxidation of hydrogen which is an inorganic compound.