Re: Nitrogen fixing in higher organisms

Alok wrote:
> Paul wrote:
> > 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;

So you mean to say that all of the proteins on the planet are made from
amino acids constructed by bacteria living on legumes millions of years
ago (supplemented by the modest amounts they continue to fix now)?

Where did we get amino acids before legume bacteria evolved? ;-)

Seriously though, aren't simple amine acids generated by the action
of lightning through the air? Blue-green cyano bacteria fix
nitrogen too. There must be lots of other organic chemical pathways 
too because there is a fairly substantial loss of nitrogen via
nitrifying bacteria. Are blue-greens everywhere and are they really
at the bottom of our food chains (at least for nitrogen building
blocks for proteins)?