Re: What did the first single-celled organisms eat?

On 11 May, 05:41, j.wilki...@xxxxxxxxx (John Wilkins) wrote:
Perplexed in Peoria <jimmene...@xxxxxxxxxxxxx> wrote:





"John Wilkins" <j.wilki...@xxxxxxxxx> wrote...
Perplexed in Peoria <jimmene...@xxxxxxxxxxxxx> wrote:

"John Wilkins" <j...@xxxxxxxxxxxxx> wrote...
John Harshman wrote:
snex wrote:

On May 9, 12:25 pm, Terry <Kilow...@xxxxxxxxxxx> wrote:

What did the first single-celled organisms eat?

each other.

They lost money on every deal, but they made it up in volume?

No, seriously, they had to have some source of energy and carbon.
There are many possibilities, some of which are still working
today. There are many inorganic processes that make high-energy
molecules, some of whose energy can be extracted. Currently living
bacteria make use of all of them. Look up, for example,
"chemautotroph".

Original organisms probably evolved as a community that was overall
autotrophic. It is speculated (for we cannot know for sure) that
they worked off volcanic flows containing H2S, but I am betting that
they would happily reuse each other's high entropy molecules as well
if they could.

And I am betting that they would if they could, but they couldn't.

Why?

Well, using foreign molecules for energy doesn't make sense to me for the
early days because my biochemical intuition says that getting useful
energy by fermentation takes some pretty sophisticated enzyme-like
machinery. Doing that came later.

I do not see why it has to be fermentation. If you have a lysed membrane
then whatever are the contents of that vesicle will be biologically
valuable, whether sugars or whatever.

The only problem I have with that is I don't see how the prerequisites
for the eater-eaten distinction are met. You can only safely take in
someone else's contents if alive/dead already has some meaning, or
else it is up for grabs who has eaten whom.

Since we are postulating
relatively primitive systems, it's likely that the intake of food
particles will be by vesicles forming on the membrane that transport
material internally, so they will almost certainly - some of them -
subsist on processed polymers from other organisms.



That leaves somehow absorbing whole molecules to become self-biomass.
Sure, that saves some kind of metabolic effort if the molecule you absorb
is something you would have needed to make anyways. But consider that
absorbing it is probably a mistake if it is not one of the molecules
normally made by your biochemistry. It may gum up your operations. So,
it is only safe and advantageous to absorb the molecule if it came from an
unfortunate member of your own 'species'. But if you think about it, that
defeats the whole reason why you postulated that they all evolved as a
community. And developing the machinery for discriminating useful foreign
molecules from the unuseful ones is also something that my intuition tells
me must have come much later. Simple inorganic foodstuffs are much easier
to 'recognize' and use in the right way.

Maybe. Organic material will denature into oligomers that are
functionally indistinguishable from abiotic organic molecules that are
of high energy or substrate-material value.

Suppose there are protobionts that routinely die in the environment,

Again, where is the alive/dead distinction, and what are the
boundaries of systems to which it applies, while we are at the point
in history between autocatalytic cycles and cellular life?

and
thus release their material, or are even predated by some simple system
that can lyse lipid membranes. The entropy of those molecules released
will be valuable to some systems, and selection will rapidly drive them
to become eficcient at it. No matter how far back you go, there has to
be an ecological web.


Another point against the idea of life reusing its own products early
on, is that it often doesn't even now. Vast thicknesses of peat,
coal, etc. are readily laid down - what a waste of primary production!


Also, I'm assuming that almost all early biomolecules were lipids, and it
is not easy energetically to pull a lipid molecule out of one membrane
(even a 'dead' one) and insert it into your own membrane. And fusing your
membrane with that of another organism runs into the same issue of "same
species, safe but ecologically pointless; different species, unsafe".

I don't see why almost all molecules that are ingested have to be lipids
(although I can see how free-floating lipids in a medium might be
valuable to the formation of the predator's membranes).



I apologize that this response has taken so long to appear (if it HAS
finally appeared!) ... Hey, why am I apologizing? It ain't my fault that
my ISP (AT&T) is technically incompetent at telecommunications.

I've been largely incommunicado for the past week myself...
--
John S. Wilkins, Postdoctoral Research Fellow, Biohumanities Project
University of Queensland - Blog: scienceblogs.com/evolvingthoughts
"He used... sarcasm. He knew all the tricks, dramatic irony, metaphor,
bathos, puns, parody, litotes and... satire. He was vicious."

.

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