Anyone know if there is a reason why prokaryotes and archaea are only singled-celled?
P.S. Yes, my grand theory of biology is coming along quite well. @@
P.S. Yes, my grand theory of biology is coming along quite well. @@
Prokaryotes & Archaea
- Thread starter Resha Caner
- Start date
Naraoia
Apprentice Biologist
They're not. Many cyanobacteria are colonial, and some (e.g. Nostoc and Anabaena) even have several different cell types, mainly "normal" photosynthetic cells and nitrogen-fixing heterocysts.
Then there are streptomycetes, which have fungus-like structures and life cycles. These are the two groups I can think of off the top of my head.
(Mind you, single-celled prokaryotes can also have different cell types, which are different phases within the life cycle of an individual cell rather than different cells within a multicelled organism. A lot of bacteria turn into dormant spores when the going gets tough.)
Can't recall any multicellular archaea, and a quick google didn't turn up any. Perhaps the ones that live in biofilms kind of count - with all the communication and exchange of stuff that goes on in a biofilm, it's almost like a multicellular organism. Or maybe more like a mini-ecosystem, given that they're not limited to single species.
(BTW: archaea are prokaryotes. "Prokaryote" is a term for cell structure, i.e. not having a well-defined membrane-bound nucleus. Bacteria and archaea are both prokaryotic.)
I'm not sure why proper multicellularity isn't more widespread among prokaryotes - though you could ask the same about eukaryotes. AFAICT, only a minority of major eukaryotic groups have gone multicellular, and some of them, like social amoebae, only do it for part of their life cycles. Perhaps being single-celled just works. It certainly allows you to reproduce like crazy.
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I'm not sure I would consider a colony a multi-cellular organism even if the colony did express different cell functions. But, the information you've provided does seem to indicate it's not a black/white issue. There is probably a spectrum of examples falling between distinctly single-cell and distinctly multi-cell. Got it.
Also, thanks for the clarification on domains. I know there are 3, but I tend to think of "bacteria" as organisms, not a domain. So, I have a bad habit of saying prokaryote when I mean the bacterial domain.
Finally, I did find a few papers on cell adhesion that get at the question I'm asking. As you implied, it does come down to a "just because" kind of answer. Bacterial adhesions tend to be virulent, so obviously that's not going to promote multi-cellularity. As soon as you get bacteria that learn to mimic something like a cadherin, you tend to get a ecto/endosymbiotic event. Voila! Multi-cellular (or, at least, development of organelles).
Also, thanks for the clarification on domains. I know there are 3, but I tend to think of "bacteria" as organisms, not a domain. So, I have a bad habit of saying prokaryote when I mean the bacterial domain.
Finally, I did find a few papers on cell adhesion that get at the question I'm asking. As you implied, it does come down to a "just because" kind of answer. Bacterial adhesions tend to be virulent, so obviously that's not going to promote multi-cellularity. As soon as you get bacteria that learn to mimic something like a cadherin, you tend to get a ecto/endosymbiotic event. Voila! Multi-cellular (or, at least, development of organelles).
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Split Rock
Conflation of Blathers
The main benefit to being single celled is your reproduction rate is throught the roof.
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The eukaryotes beat them to it. Once eukaryotes had established themselves in the mutlicellular niche it led to selection pressures favoring optimized unicellularity in prokaryotes. Multicellular and unicellular strategies each have their own advantages and weaknesses.
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Naraoia
Apprentice Biologist
The problem with that idea that I can see is that eukaryotes came much later than prokaryotes. Given that prokaryotes are clearly capable of multicellularity and had a pretty big head start, why did eukaryotes still beat them to it? (If, indeed, they did. What do you think of the idea that cyanobacteria were multicellular before eukaryotes even show up in the fossil record?)
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The fact that bacteria have evolved for unicellularity would be the biggest indicator to me. Their compact genome and interspecific gene swapping are two examples.
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I don't see any fossils of prokaryotes of the same complexity as that seen of eukaryotes in the Cambrian.
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I think the problem is energy efficacy. Eukaryotes with all those mitochondria are the only ones capable of sustaining and moving big bodies. I could be wrong of course.
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Naraoia
Apprentice Biologist
Precisely the point. They had been there for billions of years, possibly exerimented with multicellularity, and never got further than filaments with a handful of cell types. It can't just be that eukaryotes got there first, there has to be something intrinsic to prokaryotes at work.
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