Nicholas Landau <nlandau at eden.rutgers.edu> wrote :
> Is it possible that methane could serve as a respirtory
> co-substrate in acetogenesis (with CO2)? I am having a
> little trouble interpreting some data today.
>I do not think so. Methane is just a by-product, and only methanogenic
archaebacteria are able to produce it. To act as a co-substrate, methane
should act as a reducer, but it is a fairly inert molecule. It is
oxidized again by aerobic eubacteria.
CO2 dissimilation by methanogenic and acetogenic bacteria needs a low
potential reductant such as H2. I remember that CO2 can be replaced by
methanol, methylamine or formate by some methanogens.
CO2 assimilation to acetate is considered to proceed much in the same
way for acetogens and methanogens, using actyl-CoA synthase (CO
dehydrogenase = CODH).
Conversely in acetoclastic methanogens, CODH is believed to be used for
splitting acetate, discharging CO2, electrons (reducing a ferredoxin)
and a methyl group bound to an acceptor (I do not remember which one).
This methyl group is further reduced to methane. See for instance
Jablonski & Perry (1991) J.Bacteriol. 173,2481-248.
My knowledge in this field may be still too scanty, but I never heard of
methane being reoxidized for acetogenesis. After all this may not be
absurd, just thinking about the reversal of acetoclastic methanogenesis.
But this process is expected to be endergonic (about 32 kJ/mol). I you
have data showing anaerobic consumption of CH4, they are probably new
and need good attention.
I hope this post does not contain too many wrong points, please check
from other sources. Anyway I hope it did help.