Synechocystis is a genus of unicellular, freshwater cyanobacteria primarily represented by the strain Synechocystis sp. PCC6803. Synechocystis sp. PCC6803 is capable of both phototrophic growth by oxygenic photosynthesis during light periods and heterotrophic growth by glycolysis and oxidative phosphorylation during dark periods. Gene expression is regulated by a circadian clock and the organism can effectively anticipate transitions between the light and dark phases.