Letters to Nature

Nature 430, 81-85 (1 July 2004) | doi:10.1038/nature02533; Received 23 November 2003; Accepted 30 March 2004

Resilient circadian oscillator revealed in individual cyanobacteria

Irina Mihalcescu1, Weihong Hsing2,4 & Stanislas Leibler3

  1. Laboratoire de Spectrométrie Physique, Université Joseph Fourier – Grenoble I, BP87, 38402 St-Martin d'Hères Cédex, France
  2. Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA
  3. Laboratory of Living Matter and Centre for Studies in Physics and Biology, The Rockefeller University, 1230 York Avenue, New York 10021, USA
  4. Present address: Johnson & Johnson PRD, PO Box 300, Raritan, New Jersey 08869, USA

Correspondence to: Irina Mihalcescu1 Email: imihalce@spectro.ujf-grenoble.fr

Circadian oscillators, which provide internal daily periodicity, are found in a variety of living organisms, including mammals, insects, plants, fungi and cyanobacteria1. Remarkably, these biochemical oscillators are resilient to external and internal modifications, such as temperature and cell division cycles. They have to be 'fluctuation (noise) resistant'2 because relative fluctuations in the number of messenger RNA and protein molecules forming the intracellular oscillators are likely to be large. In multicellular organisms, the strong temporal stability of circadian clocks, despite molecular fluctuations, can easily be explained by intercellular interactions3, 4, 5. Here we study circadian rhythms and their stability in unicellular cyanobacteria Synechoccocus elongatus. Low-light-level microscopy has allowed us to measure gene expression under circadian control in single bacteria, showing that the circadian clock is indeed a property of individual cells. Our measurements show that the oscillators have a strong temporal stability with a correlation time of several months. In contrast to many circadian clocks in multicellular organisms, this stability seems to be ensured by the intracellular biochemical network, because the interactions between oscillators seem to be negligible.

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