The nutrition of cyanobacteria is simple. Vitamins are not required, and nitrate or ammonia is used as nitrogen source. Nitrogen-fixing species are common. Most species tested are obligate phototrophs, However, some cyanobacteria are able to grow in the dark on organic compounds, using the organic material as both carbon and energy source. Physiology of cyanobacteria:The nutrition of cyanobacteria is simple. Vitamins are not required, and nitrate or ammonia is used as nitrogen source. Nitrogen-fixing species are common. Most species tested are obligate phototrophs, However, some cyanobacteria are able to grow in the dark on organic compounds, using the organic material as both carbon and energy source. Physiology of cyanobacteria: