Bacterial photosynthesis

Cyanobacteria carry out photosynthesis using two photosystems as in green plants. Moreover, other photosynthetic bacteria, like as the purple photosynthetic bacterium Rhodospirillum rubrum which have only a single photosystem reaction center. This can hold out cyclic electron transport, producing a proton gradient and therefore synthesizing ATP (cyclic   photophosphorylation).  In other words,   a noncyclic pattern of electron transport can be carried out in that the electrons from the cytochromes pass to NAD⁺ (rather than NADP     as in green plants) to produce NADH. The electron donor is, for instance, hydrogen sulfide (H₂S) that produces sulfur (S). The Hydrogen gas (H₂) and a variety of organic compounds can also be used as electron donors by certain photosynthetic bacteria. Because H₂O is not used as electron donor, no oxygen is produced.