Stability and noise in the cyanobacterial circadian clock

Abstract

By monitoring single cyanobacterial cells in vivo we show that individual cells generate impressively stable circadian rhythms. In multicellular organisms, the circadian clock accuracy is achieved via intercellular coupling of the individual noisy oscillators. Here we demonstrate that cyanobacterial clock stability is a built-in property. We first theoretically design our experiment to be able to distinguish coupling, even weak, from phase diffusion (noise). As the precision of our evaluation increases with the length of the experiments, we continuously monitor, for a couple of weeks, mixtures of cell populations with different initial phases. The inherent experimental noise contribution, initially dominant, is reduced by enhanced statistics. We report a value of the coupling constant that is small compared to the diffusion constant of the phase. It appears therefore that the clock stability a built-in property for each bacterium.