Are cyanobacteria aerobic or anaerobic?

[Erland]

If they are aerobic, where did they get oxygen from, before cyanobacteria themselves filled the atmosphere with oxygen as a waste product of photosynthesis?

If they are anaerobic, then how can they use energy efficiently? Glycolysis alone gives little energy, and they don't have the Krebs cycle and the Electron transport chain. Do they use some other method?

 

[phinds]

What research have you done so far? What have you found?

 

[Erland]

Well, I tried Google, looked up Wikipedia, made a short search here at PF, also Quora. I didn't find any clear answer. But I admit, I didn't search for hours.

Do you have any suggestion where one quickly can find a clear answer of the question?

 

[Vagn]

Well, I tried Google, looked up Wikipedia, made a short search here at PF, also Quora. I didn't find any clear answer. But I admit, I didn't search for hours.

Do you have any suggestion where one quickly can find a clear answer of the question?

"Whereas only the Oxyphotobacteria can perform photosynthesis, there are members from all three cyanobacterial classes that are capable of aerobic respiration."

From Soo et al.

 

[BillTre]

Cyanobacteria do have an electron transport chain (see electron transport and photosynthesis in this wikipedia entry).
It is my understanding that an electron transport mechanism in the basis of metabolic power for almost all cellular organisms, most likely inherited from the last common cellular ancestor of life on earth.
The chemistry of the electron donors and acceptors, over evolutionary times or between different organisms, can vary depending upon the metabolism that has evolved. https://www.nature.com/scitable/content/the-redox-tower-of-microbial-metabolism-24272738.

how can they use energy efficiently? Glycolysis alone gives little energy, and they don't have the Krebs cycle and the Electron transport chain.

If their environment is not under intensive use by other organisms they can get away with not being particularly efficient, since they are not really competing, just surviving.

 

[Erland]

Thanks for your replies Vagn and Billtre! Interesting links.

One thing makes med confused. According to the Wikipedia link cyanobacteria "are a phylum of bacteria that obtain their energy through photosynthesis", but the Science article quoted by Vagn, talks about three classes of cyanobacteria, of which only one, Oxyphotobacteria, can perform photosynthesis.

This seems contradictory to me. Is there no agreement of what a cyanobacterium is and whether it must be able to perform photosynthesis or not?

 

[jim mcnamara]

There are disease causing cyanobacteria, for example. They are heterotrophs (no photosynthesis).
Also the same membrane system for photosynthetic processing is also used for O₂ respiration processes.

So:
1. they all started out using photosynthesis.
2. some evolved into other non-photosynthetic forms.
3. Through endosymbiosis a few ended up as plasmids in eurkaryotic cells (e.g. chromoplast, leucoplast) , somewhat like how mitochondria came to be . Because these are not free living they are no longer considered a species.

Species is a veil through which we filter the biological world, to try to make order out of a very messy situation. DNA has had a clarifying effect but the mess still remains.

 

[Prof Hugh Lefcort]

Good question. Perhaps cyanobacteria were preadapted to be tolerant of oxygen but probably used glycolysis and fermentation as a source of ATP. After they filled the world with oxygen they then evolved aerobic respiration.

 

[Chatul]

Well even before elemental oxygen was available in the atmosphere, there would still be relatively high concentrations of oxygen inside the Cyanobacteria from their own photosynthesis. So they could have aerobic respiration before then. Something I just read:

“An alternative suggestion [for the endosymbiosis with a cyanobacterium] is that the initial advantage of plastids may have simply been their uniquely useful metabolic end product, O2, as a boost to respiration in early mitochondria (Martin and Mu ̈ller 1998). The chemical benefit of O2 could, of course, have only been of value if the initial endo- symbiosis had taken place at a time in Earth’s history, or in an environment, where O2 was not freely available in sufficient amounts.”
Genomes of Stigonematalean Cyanobacteria (Subsection V) and the Evolution of Oxygenic Photosynthesis from Prokaryotes to Plastids, Dagan et al., 2012

Even if that isn’t actually the reason for the evolution of plastids, it shows that Cyanobacteria would produce enough oxygen in their cells to be a tiny aerobic environment.

 

[Steelwolf]

Good question. Perhaps cyanobacteria were preadapted to be tolerant of oxygen but probably used glycolysis and fermentation as a source of ATP. After they filled the world with oxygen they then evolved aerobic respiration.

So they filled the seas and air with a freshet of Oxygen and a tang of Alcohols, which then was a fuel and oxidizer source of life for some other bio-active critters.