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Cyanobacteria

phylum of prokaryotes
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Cyanobacteria are a taxon of bacteria which conduct photosynthesis. They are not algae, though they were once called blue-green algae. It is a phylum of bacteria, with about 1500 species. In endosymbiont theory, chloroplasts (plastids) are descended from cyanobacteria. Their DNA profile is evidence for this.[3][4][5]

Cyanobacteria
Temporal range: 3500 mya – Recent
Oscillatoria sp
Scientific classification
Domain:
Bacteria
Phylum:
Cyanobacteria
Orders

The taxonomy is under revision[1][2]

  • Unicellular forms: Chroococcales (suborders Chamaesiphonales and Pleurocapsales)
  • Filamentous (colonial) forms: Nostocales (= Hormogonales or Oscillatoriales)
  • True-branching (budding over multiple axes): Stigonematales
Structure of a cyanobacterium
O2 build-up in the Earth's atmosphere. Red and green lines represent the range of the estimates while time is measured in billions of years ago.
"Bloom" of cyanobacteria, in a pond

Cyanobacteria have an extremely long fossil record, starting at least 3,500 million years ago. They were the main organisms in the stromatolites of the Archaean and Proterozoic eons.[6]

The ability of cyanobacteria to perform oxygenic photosynthesis is highly significant. The early atmosphere on Earth was largely reducing, that is, without oxygen. The cyanobacteria in stromatolites were the first known organisms to photosynthesise and produce free oxygen. After about a billion years, the effect of this photosynthesis began a huge change in the atmosphere. The process, called the Great Oxygenation Event, took a long time. Eventually, it killed off most of the organisms which could not live in oxygen, and led to the kinds of environment we know today, where most organisms use and need oxygen.[7][8]

Light detection

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Cyanobacteria have a way of detecting light. Conrad Mullineaux, of Queen Mary University of London, said, "It has a way of detecting where the light is; we know that because of the direction that it moves".[9]

"In a single-celled pond slime, they observed how incoming rays are bent by the bug's spherical surface and focused in a spot on the far side of the cell. By shuffling along in the opposite direction to that bright spot, the microbe moves towards the light".[9]
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References

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  1. ↑ "Cyanophyceae". Access Science. doi:10.1036/1097-8542.175300. Retrieved 21 April 2011. {{cite journal}}: Cite journal requires |journal= (help)
  2. ↑ Ahoren Oren (2004). "A proposal for further integration of the cyanobacteria under the Bacteriological Code". Int. J. Syst. Evol. Microbiol. 54 (Pt 5): 1895–1902. doi:10.1099/ijs.0.03008-0. PMID 15388760.
  3. ↑ Sapp J. 1994. Evolution by association: a history of symbiosis. Oxford.
  4. ↑ Giovannoni S.J. et al 1988. Evolutionary relationships among cyanobacteria and green chloroplasts. J Bacteriol. 170: 3584–3592.
  5. ↑ Gupta, Radhey S. et al 2003. Molecular signatures in protein sequences that are characteristic of cyanobacteria and plastidhomologues. International Journal of Systematic and Evolutionary Microbiology. 53, 1833-1842. Gupta, R[permanent dead link]
  6. ↑ Knoll, Andrew H. 2004. Life on a young planet: the first three billion years of evolution on Earth. Princeton, N.J. ISBN 0-691-12029-3
  7. ↑ Frei R. et al 2009. Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes. Nature 461 (7261): 250–253. Abstract: [1]
  8. ↑ Holland, Heinrich D. 2006. The oxygenation of the atmosphere and oceans. Phil. Trans. R. Soc. B, 361, p. 903–915. [2]
  9. ↑ 9.0 9.1 Webb, Jonathan 2016. Bacteria 'see' like tiny eyeballs. BBC News Science & Environment. [3]
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