Self-sustained rhythmic behavior of sp. PCC 6803 under continuous light conditions in the absence of light-dark entrainment.

Circadian clocks regulate biological activities, providing organisms with a fitness advantage under diurnal conditions by enabling anticipation and adaptation to recurring external changes. Three proteins, KaiA, KaiB, and KaiC, constitute the circadian clock in the cyanobacterial model PCC 7942. Several techniques established to measure circadian output in yielded comparably weak signals in sp. PCC 6803, a strain important for biotechnological applications. We applied an approach that does not require genetic modifications to monitor the circadian rhythms in and . We placed batch cultures in shake flasks on a sensor detecting backscattered light via noninvasive online measurements. Backscattering oscillated with a period of ∼24 h around the average growth. Wavelet and Fourier transformations are applied to determine the period's significance and length. In , oscillations fulfilled the circadian criteria of temperature compensation and entrainment by external stimuli. Remarkably, dilution alone synchronized oscillations. Western blotting revealed that the backscatter was ∼6.5 h phase-delayed in comparison to KaiC3 phosphorylation.