Index >> Bacterial Photosynthesis >> Cyanobacteria (Formerly Blue Green Algae) Blue Green Bacteria

The source of hydrogen is water. Respiration is aerobic. The Cyanobacteria are gram negative. Many are motile. Motility is of the gliding type as in motile green bacteria. The photosynthetic apparatus is located in a series of thylakoids or membranous sacs which contain chlorophyll a and carotenoids, the 'photochemical reaction' centres and the photosynthetic electron transfer chain.

In the 50 nm space between the thylakoids are disc shaped objects, '40 nm' in diameter, called phycobilisomes. They contain phycobiliproteins (PBPs), the major light harvesting pigment. In Synecchococcus and Pseudanabaena there are 2-5 parallel thylakoids in the cortical region of the bacterial cell. In most Cyanobacteria the thylakoids are convoluted, and occupy a much larger area of the cell.

Components of the Photosynthetic electron transport system (e.g. ferredoxin, plastocyanin and cytochrome f) have been located in the thylakoid membrane. The only chlorophyll found in the Cyanobacteria is chlorophyll a. This is an important homology with chloroplasts. There are two photosystems I and II. Photosystem I almost exclusively receives the light energy harvested by chlorophyll, and only cyclic photophosphorylation takes place, β-carotene is always present, and is usually accompanied by either or both oxycarotenoids, zeanthin and echinone.
In addition most Cyanobacteria synthesize group specific pigments, notably carotenoid glycosides. Phycobiliproteins are the major light-harvesting pigments of the Cyanobacteria. (These are also found in the red algae). Light energy absorbed by the PBPs is transfered mainly to photosystem II. Each pap is composed of two different polypeptide chains α and β, each carrying at least one bilin chromatophore attached io it covalently. The α and β monomers form the native protein oligomers, (αβ) n.