Principles of rhythmicity emerging from cyanobacteria

Over the past 25 years the cyanobacterium Synechococcus elongatus has dazzled the circadian rhythms community by revealing in exquisite detail the mechanism of its prokaryotic circadian clock. So many aspects of the timing machinery are surprising that attention has largely centered on the ways in which the cyanobacterial clock is different from the circadian clocks of eukaryotic organisms. Perhaps just as remarkable is the similarity of circadian properties between eukaryotic and prokaryotic species – a testament to the universality of unfaltering daily cues in the environment and shared metabolic needs of biological systems as selective agents over evolutionary time. Like the clocks of animals and plants, the S. elongatus clock supports near-24-h rhythms that persist in constant conditions, entrains to daily cycles of light or temperature, is differentially sensitive to cues at different points in the cycle, and tunes its daily period depending on the intensity of the ambient light environment. Remarkably, it supports these properties with a nanomachine mechanism that is discrete and can be reassembled to function outside of the cell. The lessons learned from the S. elongatus clock underscore the power of genetics to reveal mechanisms whose natures are not known a priori, and speak to the value of collaboration to apply diverse skillsets to solve difficult biological problems