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Cyanobacterial circadian clock

The coordination of biological activities into daily cycles provides an important advantage for the fitness of diverse organisms. An internal circadian oscillator drives gene expression in an approximate 24 hours rhythm. The period of this free-running rhythm is highly robust against many changes in the natural environment, for example, in cyanobacteria the clock can compensate for variations in the ambient temperature. But for certain external stimuli (e.g. light, nutrients), the circadian rhythm can be entrained. For the cyanobacterium Synechococcus elongatus, a robust circadian rhythm has been observed under constant darkness conditions and even for complete suppression of the cellular transcription and translation activity. Moreover, only three different cyanobacterial proteins (KaiA, KaiB, and KaiC) are sufficient to achieve a temperature-compensated circadian rhythm of phosphorylation cycles in vitro. KaiC as the major clock component has three intrinsic enzymatic activities: autokinase, autophosphatase and ATPase activities, whereas KaiA enhances the kinase and KaiB the autophosphatase activities, respectively. Thus, in contrast to eukaryotic clock models the cyanobacterial core oscillator operates independently of transcription and translation processes. Most data on the circadian timing process in cyanobacteria have been obtained using the unicellular cyanobacterium Synechococcus elongatus PCC 7942. In different strains of the marine cyanobacteria of the genus Prochlorococcus, components of the oscillator and of the in- and output pathways are missing or truncated. Other model cyanobacteria like Synechocystis sp. PCC 6803 or the filamentous strain Anabaena sp. PCC 7120 harbour multiple gene copies for the three clock components. In this project we analyze non-standard circadian clocks of cyanobacteria.



Dr. Ilka Axmann,  Heinrich Heine Universität Düsseldorf, Synthetische Mikrobiologie



Dörrich AK, Mitschke J, Siadat O, Wilde A. (2014) Deletion of the Synechocystis sp. PCC 6803 kaiAB1C1 gene cluster causes impaired cell growth under light-dark conditions. Microbiology 160, 2538-2550.


Axmann IM, Hertel S, Wiegard A, Dörrich AK, Wilde A. (2014) Diversity of KaiC-based timing systems in marine Cyanobacteria. Mar. Genomics. 14, 3-16.


Wiegard A, Dörrich AK, Deinzer HT, Beck C, Wilde A, Holtzendorff J, Axmann IM. (2013) Biochemical analysis of three putative KaiC clock proteins from Synechocystis sp. PCC 6803 suggests their functional divergence. Microbiology 159, 948-958.


Axmann, I.M., Dühring, U., Seeliger, L., Arnold, A., Vanselow, J.T., Kramer, A., Wilde, A. (2009) Biochemical evidence for a timing mechanism in Prochlorococcus. J. Bacteriol. 191, 5342-5347.


Clodong, S., Dühring, U., Kronk, L., Wilde, A., Axmann, I., Herzel, H., Kollmann, M. (2007) Functioning and robustness of a bacterial circadian clock. Molecular Systems Biology 3:90. Epub 2007 Mar 13.


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