Nitrogen fixing in higher organisms

Paul wrote:

> Stephen.Pushak wrote:
> >
> >all this talk about CO2 and O2 and N2 in solution. Here's a new
> >question: do fishes contribute to the nitrogen compounds in
> >solution (ammonia, nitrates etc.) by consuming gaseous nitrogen
> >and converting it somehow? We know that under certain circumstances
> >bacteria will convert nitrogen compounds back to gaseous nitrogen
> >which would result in a net loss of nitrogen in the system (ignoring
> >additions of fertilizers, food and new aquatic creatures)
> >
> Nope, you and I and the fish in our aquariums are unable to fix nitrogen to
> form proteins. We have to get our proteins from our food so if the N is not
> already bound up in an amino acid it won't do us any good. Some bacteria,
> I'm sure you're familar with nitrogen fixing bacteria on legume roots, have
> the capability of converting N2 into compounds usable by plants.


> To my knowledge there are no higher level organisms that can fix N2. I'm
> not however sure about whether intestinal bacteria in some herbivores can
> fix N2. A cow eats grass to feed cellulose digesting organisms in it's gut,
> which are in turn consumed by the cow. Perhaps a biologist can help here,
> it is my understanding that the bacteria in the cow's stomach convert the
> cellulose to sugars but get protein forming nitrogen in the protein from
> the grass.

	The intestinal bacteria in ruminants may very will have the
capability to fix nitrogen, although, they don't get much of it down
there. They probably just use nutients that the cow ingests in the grass;
they may not need to breakdown the proteins themselves, however, since the
cows digestive enzymes probably do most of that work for them. Aside from
the fact that the cows gain the useable sugar from the cellulose, they
also gain a plethera of other nutrients -- vitamins mainly, from the
bacteria.  One of the major by-products of this whole process that we are
very familiar with is good ol' CH4. 
	Humans really do the same thing as our bovine cousins, we just
don't possess the same fermentation chambers and special cellulose
digesting bacteria that the cows do.  However, we use bacteria also, E. 
coli, L. acidophilus, etc..., to supply ourselves with nutrients such as
vitamin K. We also depend on these bacteria to digest sugars like maltose
(found in beans). And, yes, one of the by-products of maltose digestion is
	A healthy person has about a pound of bacteria in their gut...
With ruminants, that number is probably on a different order of magnitude.