I know that anaerobic bacteria don’t require oxygen to produce/utilize energy. But would it be possible to have an entirely anaerobic ecosystem, complete with large animals, which didn’t utilize or require oxygen?
I don’t know enough biochemistry to go very far with this, but I think a lot would depend on how complex you want the ecosystem to be.
IIRC, one of the problems with anaerobic beasties is that there is not as much energy available to their systems as there is to aerobic (oxygen-using) organisms. This might severely limit how big/complex they might be.
Other than that, I dunno…
There’s oxygen in water.
Those organisms use amino acids to make proteins. The ‘acid’ part of all 20 common amino acids is an oxygen containing carboxyl (COOH) group.
Sugars are alcohols; with oxygen in the OH groups.
DNA contains sugars, hence oxygen.
You’d have to do a lot of redesign to eliminate oxygen.
hmmmmm… I don’t think that that is what the op is asking.
I could be wrong, but I read this: “don’t require oxygen to produce/utilize energy” as asking whether there were systems where oxygen was not being used as an energy source. You are, of course, correct in saying that oxygen is in some form being used in the kinds of systems that I linked to, but I don’t think that that is what the op was thinking about. Considering that, so far as we know, all life is based on water, then it is impossible to have life without oxygen. (The existance of silicon life-forms that do no at all use oxygen is, I think, something that no one here is able to decisively comment on.)
The point of my link was to show that there exist reduced-chemistry ecosystems present on Earth where large (i.e. multicellular) organisms exist. Tube-worms, for instance, can (IIRC) grow to around half a meter or longer.
Yes, but the tube-worms, or more precisely their symbiont chemosynthetic bacteria, *do * use oxygen in their metabolism.
From here
While anaerobic ecosystems are certainly possible, they may not produce enough energy to support organisms much larger than bacteria.
They’re not only possible - they exist (depending on your definition of “ecosystem”) but there certainly are microbial ecosystems in anaerobic environments. The examples that come to mind are marsh mud and mudflats. Typically here on the west coast of North America you’ll find anaerobic sediments within a few centimeters of the mud surface. The smell of rotten eggs associated with it is the result of the production of H[sub]2[/sub]S due to anaerobic bacteria and you can usually visually identify the anaerobic zone by its dark black color. Larger organisms (worms, clams) burrowing in the anaerobic mud create local pockets where oxygen becomes available, and these are inhabited by smaller aerobic organisms that generally have competitive advantage over anaerobes in oxygenated environments - but the effect quickly dies off with distance and the only things larger than bacteria are found in the oxygenated areas.
Here’s an article about productivity of bacteria in such sediments:
http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=ENV&recid=3934816
Scroll down on this page to find references to biological activity, again, probably just bacteria, deep in the Earth’s crust and beneath the sea floor, where presumably oxygen isn’t available (until we drill into it to take a sample, that is shrug):
http://www.issm.net/issm99abstracts.htm
I didn’t mean to imply that they didn’t exist. Another place anaerobic ecosystems exist is in deep subsurface environments.
It might also be mentioned that life on Earth flourished in an anaerobic environment for the first 1.5 billion years of its existence.
Very interesting link. Shows you what I know. (Appearently less about hydrothermal vent systems than I thought.)
This is kind of what I was wondering–if you could have an ecosystem with large-ish (say, mouse-size) beasties running about using energy that was not derived from oxygen, but from some anaerobic process. It looks like the answer is ‘no.’
Is there a simple answer to the question of why anaerobic processes have such a smaller energy yield than aerobic ones?
I thought that some thinking in paleobiology has it that Earth was mainly an anerobic environment, life-wise, and that at some point Oxygen kicked in, creating a species crisis in which aerobic life took over and anerobic life pretty much vanished.
Although it does persist in or near those geothermal vent thingies at the bottom of the ocean, and in some other places.
The answer is probably yes.
I’m not sure what Colibri’s point was, but there is no animals much larger than bacteria are quite capable of thriving using just anaerobic respiration. He may have meant that the productivity of anaerobic systems in toto wouldn’t yield enough energy to support organisms larger then bacteria, but that makes no real sense. Organisms the size of mice and rats might be the equivalent of whales in such a system but there is no obvious productivity limitation barring such monstrosities just as there is no limitation on tiny organism feeding whale sharks and whales. Many organisms now such as roundworms, molluscs and even fish derive a considerable portion of their energy form anaerobic sediments.
I suspect that the truth is that such complete systems haven’t developed on earth simply because oxygen is omnipresent. Bacteria can manage to remain anaerobes because they can find anaerobic niches in sediments or inside soil particles but it’s much harder for macroscopic organisms to remain exclusively in those niches. Large animals must have the capacity to move and burrow, and in so doing they immediately open themselves up to competition from aerobic animals burrowing down for above. As a result all the big sediment feeders are able to return to the surface where utilising oxygen gives them a massive edge.
On a truly anaerobic world where there is no overlying layer of oxygenated water there would be no advantage to such behaviour and anaerobic organisms the size of mice could live quite readily, though large clams would probably be the largest life forms.
Basically the body derives energy by stripping electrons off the food you eat and using those electrons to generate a tiny electrical charge to run the tiny electric pumps that keep you alive and moving. Animal cells are essentially just tiny electrochemical motors.
The catch is that those stripped electrons have to go somewhere, they have to be moved to a lower energy state and disposed of in order to derive that energy. Oxygen is ideal for disposing of electrons because it is extremely electron hungry. It will accept electrons from almost anything. Because of that electron affinity we can take the electrons we strip off food run them down to a very low energy state, sucking almost all the energy from them, and then we can dump them onto oxygen which still accepts them. In comparison other elements are pretty lousy electron acceptors. Once the electrons cease being very high energy those other compounds simply won’t accept them. As a result running anaerobically requires that the electrons be disposed of while they still have a lot of energy in them, so the organism gets less usable energy for each calorie eaten.
You might compare it to a battery recycler. One place will accept batteries for disposal that are totally dead and another will only accept batteries if they have a few hours life left in them. Obviously the place that will accept the dead batteries will be more efficient to use. Oxygen vs. other electron acceptors is very much like that. Oxygen allows us to suck every last little bit of juice out of our food, other electron acceptors require us to discard the food with quite a bit of potentially usable juice left.
The Earth is still very much dominated by anaerobic life both in terms of individuals and mass but probably also in terms of species.
Only a very thin layer at the top of the biosphere is dominated by aerobic organisms. Within a few inches of the top of the soil or sediment anaerobes dominate and they continue to dominate for the next several miles down.
Add to that the fact that most aerobic organisms are host to countless billions of anaerobes and it kinds of puts it in perspective. Your body contains the cells of far more facultative anaerobes than it does human cells.
That kind of puts paid to any notion that Earth has ever been other than dominated by anaerobic life. You don’t need to go looking in geothermal vents for anaerobic life, over 90% of the organisms on your house are anaerobes.
Awesome, Blake. You get the Special SDMB Gold Star for 'Splainin Stuff.