Phototrophic green bacteria, phototrophic purple bacteria, and heliobacteria are three groups of bacteria that use anoxygenic photosynthesis. Anoxygenic phototrophs have photosynthetic pigments called bacteriochlorophylls. Bacteriochlorophyll a and b have maxima wavelength absorption at 775 nm and 790 nm, respectively in ether. Unlike oxygenic phototrophs, anoxygenic photosynthesis only functions using a single photosystem. This restricts them to cyclic electron flow only, and they are therefore unable to produce O2 from the oxidization of H2O. In plants, algae and cyanobacteria, the photosynthetic processes results not only in the fixation of carbon dioxide (CO2) from the atmosphere but also release of molecular oxygen to the atmosphere. This process is known as oxygenic.
