PNAS nexusMay 7, 2025

Self-maintained rhythmic activity of Synechocystis bacteria under constant light without day-night cues

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗OA ↗

Updated Mar 30, 2026

Abstract

Backscattering light measurements indicated a circadian rhythm with a period of approximately 24 hours in the cyanobacterial strain PCC 6803.

Circadian clocks help organisms adapt to daily changes in their environment.
The proteins KaiA, KaiB, and KaiC are key components of the circadian clock in cyanobacteria.
A new non-invasive method detected circadian rhythms in PCC 6803 without genetic modifications.
The observed oscillations met criteria for temperature compensation and responsiveness to external signals.
Dilution of cultures was sufficient to synchronize the observed oscillations.
Backscatter measurements were found to be approximately 6.5 hours delayed compared to KaiC phosphorylation.

Simplified

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 modelPCC 7942. Several techniques established to measure circadian output inyielded comparably weak signals insp. PCC 6803, a strain important for biotechnological applications. We applied an approach that does not require genetic modifications to monitor the circadian rhythms inand. 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. Synechococcus elongatus Synechococcus Synechocystis Synechococcus Synechocystis Synechocystis

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Self-maintained rhythmic activity of Synechocystis bacteria under constant light without day-night cues

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