Emergence of Synechococcus Elongatus Pcc 7942 as a Prokaryotic Model Organism for Circadian

Initial observations of what are now accepted as clockcontrolled processes in cyanobacteria were reported in the mid-1980s by scientists working with natural isolates of diverse species (Ditty et al. 2003). Diurnal rhythms in nitrogen fixation, photosynthesis, amino acid uptake, and cell division were not immediately interpreted as the consequence of an endogenous biological clock. At least two groups recognized that these rhythms were reminiscent of eukaryotic circadian cycles (Sweeney and Borgese 1989; Huang et al. 1990), and T.-C. Huang’s group performed experiments to demonstrate that rhythms of amino acid uptake in Synechococcus (now Cyanothece) RF-1 persist under constant conditions, reset the timing of peak activity in response to an environmental signal, and are temperature-compensated (Huang et al. 1990). With these three criteria fulfilled, a cyanobacterial rhythm was demonstrated to share the hallmarks of eukaryotic circadian rhythms (Dunlap et al. 2004).