Cyanothece the process of fixing nitrogen became unfavorable, and natural selection eliminated some of the necessary genes for the nitrogenase protein complex to increase evolutionary fitness. Cyanobacteria turn energy from the sun into chemical energy through oxygenic photosynthesis. Their light-harvesting complex that captures the photons usually includes the pigments chlorophyll a and phycocyanin. A cyanobacterium’s typical blue-green color is a result of the combination of these two pigments. Three "Cyanothece" strains, sp. PCC 7424, 7822 and 8801, have the additional pigment phycoerythrin, which expands the wavelengths of light these species use for energy. Phycoerythrin also gives these three species a brownish-green
Chlorophyll directly absorbing light and performing charge separation events without the assistance of other chlorophyll pigments, but the probability of that happening under a given light intensity is small. Thus, the other chlorophylls in the photosystem and antenna pigment proteins all cooperatively absorb and funnel light energy to the reaction center. Besides chlorophyll "a", there are other pigments, called accessory pigments, which occur in these pigment–protein antenna complexes. Chlorophylls are numerous in types, but all are defined by the presence of a fifth ring beyond the four pyrrole-like rings. Most chlorophylls are classified as chlorins, which are reduced relatives to porphyrins