Cyanobacteria

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.Sapp J. 1994. Evolution by association: a history of symbiosis. Oxford.Giovannoni S.J. et al 1988. Evolutionary relationships among cyanobacteria and green chloroplasts. J Bacteriol. 170: 3584–3592.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

Cyanobacteria have an extremely long fossil record, starting  at least 3.5 billion years ago. They were the main organisms in the stromatolites of the Archaean and Proterozoic eons.Knoll, Andrew H. 2004. Life on a young planet: the first three billion years of evolution on Earth. Princeton, N.J. 

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 photosynthesize 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.Frei R. et al. 2009. Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes. Nature 461 (7261): 250–253. Abstract: Holland, Heinrich D. 2006. The oxygenation of the atmosphere and oceans. Phil. Trans. R. Soc. B, 361, p. 903–915.  

 Light detection 
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".Webb, Jonathan 2016. Bacteria 'see' like tiny eyeballs. BBC News  Science & Environment. 
"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".

Related pages
 Ice algae

 References 

Category:Gram-negative bacteria
Category:Cell biology
Category:Photosynthesis