"Spark of life: Metabolism appears in lab without cells "

[klaus54]

Releasing oxygen. I think I have part of my answer, though. It seems that releasing oxygen isn't necessary, and that there were (are?) anoxygenic photosynthetic processes. Now I wonder how advanced anaerobic lifeforms could get.

Thermophiles aren't photosynthetic. Their external source of energy to drive metabolism is low entropy heat (i.e., high temperature.) They don't make their own "food", they are not autotrophs.

Someone with a better biological background than me could explain this better.

K54

[sylas]

Thermophiles aren't photosynthetic. Their external source of energy to drive metabolism is low entropy heat (i.e., high temperature.) They don't make their own "food", they are not autotrophs.

Yes.

However, there is apparently an anoxygenic photosynthetic process. You can find an introduction at wikipedia: "Anoxygenic photosynthesis".

Quoting the overview:

Anoxygenic photosynthesis is the phototrophic process where light energy is captured and converted to ATP, without the production of oxygen. Water is therefore not used as an electron donor. There are several groups of bacteria that undergo anoxygenic photosynthesis: Green sulfur bacteria, green and red filamentous anoxygenic phototrophs (FAPs), phototrophic purple bacteria, phototrophic Acidobacteria, and phototrophic heliobacteria.[1][2]

Anoxygenic phototrophs have photosynthetic pigments called bacteriochlorophylls (similar to chlorophyll found in eukaryotes). Bacteriochlorophyll a and b have wavelengths of maximum absorption at 775 nm and 790 nm, respectively in ether. In vivo however, due to shared extended resonance structures, these pigments were found to maximally absorb wavelengths out further into the near-infrared. Bacteriochlorophylls c-g have the corresponding "peak" absorbance at more blue wavelengths when dissolved in an organic solvent, but are similarly red-shifted within their natural environment (with the exception of bacteriochlorophyll f, which has not been naturally observed).

Unlike oxygenic phototrophs, anoxygenic photosynthesis only functions using (by phylum) either one of two possible types of photosystem. This restricts them to cyclic electron flow and are therefore unable to produce O2 from the oxidization of H2O.

These bacteria are not thermophiles, I am pretty sure.

Cheers -- sylas

[Carrikature]

Yes.

However, there is apparently an anoxygenic photosynthetic process. You can find an introduction at wikipedia: "Anoxygenic photosynthesis".

Quoting the overview:

Anoxygenic photosynthesis is the phototrophic process where light energy is captured and converted to ATP, without the production of oxygen. Water is therefore not used as an electron donor. There are several groups of bacteria that undergo anoxygenic photosynthesis: Green sulfur bacteria, green and red filamentous anoxygenic phototrophs (FAPs), phototrophic purple bacteria, phototrophic Acidobacteria, and phototrophic heliobacteria.[1][2]

Anoxygenic phototrophs have photosynthetic pigments called bacteriochlorophylls (similar to chlorophyll found in eukaryotes). Bacteriochlorophyll a and b have wavelengths of maximum absorption at 775 nm and 790 nm, respectively in ether. In vivo however, due to shared extended resonance structures, these pigments were found to maximally absorb wavelengths out further into the near-infrared. Bacteriochlorophylls c-g have the corresponding "peak" absorbance at more blue wavelengths when dissolved in an organic solvent, but are similarly red-shifted within their natural environment (with the exception of bacteriochlorophyll f, which has not been naturally observed).

Unlike oxygenic phototrophs, anoxygenic photosynthesis only functions using (by phylum) either one of two possible types of photosystem. This restricts them to cyclic electron flow and are therefore unable to produce O2 from the oxidization of H2O.

These bacteria are not thermophiles, I am pretty sure.

Cheers -- sylas

That's what I had found.

[Carrikature]

Thermophiles aren't photosynthetic. Their external source of energy to drive metabolism is low entropy heat (i.e., high temperature.) They don't make their own "food", they are not autotrophs.

Someone with a better biological background than me could explain this better.

K54

Right. That part I knew. Thermophiles are distinct from anoxygenic phototrophs. Still, it's an interesting question if thermophiles would be able to absorb enough energy to support more complex forms. It seems there would be an upper limit hit pretty quickly, but that probably depends on the environment.