Cyanothece

Cyanothece is a genus of unicellular, diazotrophic, oxygenic photosynthesizing cyanobacteria. In 1976, Jiří Komárek defined the prokaryotic cyanobacteria genus Cyanothece as distinct from Synechococcus NAG 1949. Organisms in both genera share characteristics in addition to being oxygenic phototrophs. They are both unicellular, forming aggregates, but not found in mucilaginous colonies. They may have a thin mucilage layer around each cell. Both genera also divide by binary fission along an axis perpendicular to the cell's longitudinal axis. A handful of characteristics distinguish the two genera. While Synechococcus species are usually cylindrical, Cyanothece species are normally oval and longer than 3 μm., Cyanothece’s outer cell wall layer is relatively thick and contains spherical, glassy vesicles whose function has yet to be defined. Cyanothece’s nucleoids are spread loosely throughout the cell, with a net-like appearance. Instead of concentric thylakoid membranes that share a center or axis, Cyanothece’s exhibit short, wavy and radially arranged., All Cyanothece had nitrogenase activity at one time; although some strains have lost the necessary genes. During nitrogen-fixing conditions, Cyanothece creates inclusion storage bodies under the control of a circadian rhythm. Between 2.5 and 3.0 billion years ago, cyanobacteria started using the energy from light to split water, releasing oxygen into the anaerobic, reducing environment. Parts of this ancient cyanobacterial metabolism are still maintained today. Bandyopadhyay et al. 2011 created a phylogenic tree for cyanobacteria using 226 homolog protein groups. They grouped five of the six major Cyanothece strains (PCC 7424, PCC 7822, ATCC 51142, PCC 8801, PCC 8802) as belonging to a single clade, but had Cyanothece sp PCC 7425 branched off earlier. PCC 7425's nitrogenase cluster is arranged differently from the other five strains and can only fix nitrogen anaerobically. Most other cyanobacteria may have lost their ability to fix nitrogen.