PVC may have played a big part in our evolution...
But, no I'm not talking about polyvinyl chloride (sorry to dissapoint!), I'm talking about the Planctomycetes, Verrucomicrobia, Chlamydiae (PVC) bacterial superphylum. And I'm talking waaaay back, when the Chlamydiae were much more innocent and hadn't got into that whole sexually transmitted disease scene.
In a Science article, Devos and Reynaud discuss the possibility that that The PVC bugs, which appear to be a monophyletic group forming their own "superphylum" are in fact the most likely candidates for the bacterial ancestor of archaea and eukaryotes. The evidence for this comes from the fact that some (but not all) PVC members share several features in common with eukaryotes, such as subcellular compartmentalisation, and membrane bound DNA. Some of these features are also shared with archaea, such as loss of the FtsZ protein. PVC bacteria, archaea and eukaryotes also share another protein absense... but that will be discussed in one of our forthcoming papers.
Of the PVC bacteria, Gemmata obscuriglobus is perhaps the most interesting. It surrounds its DNA in a membrane, reminiscent of the eukaryotic nucleus, and seems to undergo a process similar to endocytosis for uptake of extracellular material.
Devos and Reynaud suggest that the PVC bacteria are evolutionary intermediates on the road to eukaryotes and archaea, but as far as I know there is no phylogenomic evidence that suggests PVC bacteria are more closely related to eukaryotes and archaea than the rest of bacteria. Instead, I wonder whether these features are instead relics from LUCA, which as I mentioned in a previous post, might have been surprisingy complex and eukaryote-like. Could the lack of some of these features in other bacteria in fact be a derived, rather than ancestral state?
EDIT:
It seems the hypothesis doesn't hold up to scrutiny, and in fact "all of the PVC traits that are currently cited as evidence for aspiring eukaryoticity are either analogous (the result of convergent evolution), not homologous, to eukaryotic traits; or else they are the result of horizontal gene transfers."
See:
Planctomycetes and eukaryotes: A case of analogy not homology.
http://www.ncbi.nlm.nih.gov/pubmed/21858844
-------
Devos, D., & Reynaud, E. (2010). Intermediate Steps Science, 330 (6008), 1187-1188 DOI: 10.1126/science.1196720
Fuerst JA, & Webb RI (1991). Membrane-bounded nucleoid in the eubacterium Gemmatata obscuriglobus. Proceedings of the National Academy of Sciences of the United States of America, 88 (18), 8184-8 PMID: 11607213
Lonhienne, T., Sagulenko, E., Webb, R., Lee, K., Franke, J., Devos, D., Nouwens, A., Carroll, B., & Fuerst, J. (2010). From the Cover: Endocytosis-like protein uptake in the bacterium Gemmata obscuriglobus Proceedings of the National Academy of Sciences, 107 (29), 12883-12888 DOI: 10.1073/pnas.1001085107
But, no I'm not talking about polyvinyl chloride (sorry to dissapoint!), I'm talking about the Planctomycetes, Verrucomicrobia, Chlamydiae (PVC) bacterial superphylum. And I'm talking waaaay back, when the Chlamydiae were much more innocent and hadn't got into that whole sexually transmitted disease scene.
In a Science article, Devos and Reynaud discuss the possibility that that The PVC bugs, which appear to be a monophyletic group forming their own "superphylum" are in fact the most likely candidates for the bacterial ancestor of archaea and eukaryotes. The evidence for this comes from the fact that some (but not all) PVC members share several features in common with eukaryotes, such as subcellular compartmentalisation, and membrane bound DNA. Some of these features are also shared with archaea, such as loss of the FtsZ protein. PVC bacteria, archaea and eukaryotes also share another protein absense... but that will be discussed in one of our forthcoming papers.
Of the PVC bacteria, Gemmata obscuriglobus is perhaps the most interesting. It surrounds its DNA in a membrane, reminiscent of the eukaryotic nucleus, and seems to undergo a process similar to endocytosis for uptake of extracellular material.
Devos and Reynaud suggest that the PVC bacteria are evolutionary intermediates on the road to eukaryotes and archaea, but as far as I know there is no phylogenomic evidence that suggests PVC bacteria are more closely related to eukaryotes and archaea than the rest of bacteria. Instead, I wonder whether these features are instead relics from LUCA, which as I mentioned in a previous post, might have been surprisingy complex and eukaryote-like. Could the lack of some of these features in other bacteria in fact be a derived, rather than ancestral state?
EDIT:
It seems the hypothesis doesn't hold up to scrutiny, and in fact "all of the PVC traits that are currently cited as evidence for aspiring eukaryoticity are either analogous (the result of convergent evolution), not homologous, to eukaryotic traits; or else they are the result of horizontal gene transfers."
See:
Planctomycetes and eukaryotes: A case of analogy not homology.
http://www.ncbi.nlm.nih.gov/pubmed/21858844
-------
Devos, D., & Reynaud, E. (2010). Intermediate Steps Science, 330 (6008), 1187-1188 DOI: 10.1126/science.1196720
Fuerst JA, & Webb RI (1991). Membrane-bounded nucleoid in the eubacterium Gemmatata obscuriglobus. Proceedings of the National Academy of Sciences of the United States of America, 88 (18), 8184-8 PMID: 11607213
Lonhienne, T., Sagulenko, E., Webb, R., Lee, K., Franke, J., Devos, D., Nouwens, A., Carroll, B., & Fuerst, J. (2010). From the Cover: Endocytosis-like protein uptake in the bacterium Gemmata obscuriglobus Proceedings of the National Academy of Sciences, 107 (29), 12883-12888 DOI: 10.1073/pnas.1001085107
A very interesting blogpost.
ReplyDeleteDo you know the work of Labedan ? They would agree with the idea that bacteria were 'streamlined' and lost some features with respect to LUCA
http://www.biology-direct.com/content/3/1/29
Thanks for the link! Interesting that they support the notion of an RNA genome LUCA. Hmmm I might read into the evidence for that a bit more and blog about it later :)
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