From pond to platform: how <i>Synechocystis</i> sp. PCC 6803 became the default model cyanobacterium

Cyanobacteria are an ancient clade of phototrophic prokaryotes responsible for the initial oxygenation of the Earth's atmosphere and still remain as major contributors to the productivity of the biosphere. Apart from their ecological importance, they are widely used as model organisms in photosynthesis research and show great potential for green biotechnology. Cyanobacteria are united by their specialized phototrophic metabolism but are otherwise extremely diverse in habitat, physiological adaptations, and morphology: they range from tiny unicellular species to complex multicellular forms with multiple specialized cell types. Out of all the vast range of cyanobacteria available, why did <i>Synechocystis</i> sp. PCC 6803 become the default laboratory model? Here, we recount its early history as a laboratory model and the key decisions that led to its establishment as the go-to cyanobacterium. We explain its advantages and limitations as a model organism, along with key advances in understanding that have been enabled by <i>Synechocystis</i> research. Finally, we discuss the role of <i>Synechocystis</i> in ongoing basic and applied research.