title: Ultradian metabolic rhythm in the diazotrophic cyanobacterium Cyanothece sp. ATCC 51142.
abstract: The unicellular cyanobacterium Cyanothece sp. American Type Culture Collection (ATCC) 51142 is capable of performing oxygenic photosynthesis during the day and microoxic nitrogen fixation at night. These mutually exclusive processes are possible only by temporal separation by circadian clock or another cellular program. We report identification of a temperature-dependent ultradian metabolic rhythm that controls the alternating oxygenic and microoxic processes of Cyanothece sp. ATCC 51142 under continuous high irradiance and in high CO2 concentration. During the oxygenic photosynthesis phase, nitrate deficiency limited protein synthesis and CO2 assimilation was directed toward glycogen synthesis. The carbohydrate accumulation reduced overexcitation of the photosynthetic reactions until a respiration burst initiated a transition to microoxic N2 fixation. In contrast to the circadian clock, this ultradian period is strongly temperature-dependent: 17 h at 27 °C, which continuously decreased to 10 h at 39 °C. The cycle was expressed by an oscillatory modulation of net O2 evolution, CO2 uptake, pH, fluorescence emission, glycogen content, cell division, and culture optical density. The corresponding ultradian modulation was also observed in the transcription of nitrogenase-related nifB and nifH genes and in nitrogenase activities. We propose that the control by the newly identified metabolic cycle adds another rhythmic component to the circadian clock that reflects the true metabolic state depending on the actual temperature, irradiance, and CO2 availability.
authors.affiliation: Global Change Research Centre-CzechGlobe, Academy of Sciences of the Czech Republic, 664 24 Drásov, Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Červený
authors.forename: Maria A
authors.initials: MA
authors.lastname: Sinetova
authors.forename: Luis
authors.initials: L
authors.lastname: Valledor
authors.forename: Louis A
authors.initials: LA
authors.lastname: Sherman
authors.forename: Ladislav
authors.initials: L
authors.lastname: Nedbal
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D019149:Bioreactors / Q000382:microbiology; D002245:Carbon Dioxide / Q000378:metabolism; D002940:Circadian Rhythm / Q000235:genetics / Q000502:physiology*; D046889:Cyanothece / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D018507:Gene Expression Regulation, Developmental; D006003:Glycogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D009586:Nitrogen Fixation / Q000235:genetics / Q000502:physiology*; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D001426:Bacterial Proteins; C092498:NifB protein, Bacteria; D002245:Carbon Dioxide; D006003:Glycogen; D010088:Oxidoreductases; C029130:nitrogenase reductase; D010100:Oxygen
keywords: cyanobacteria; diurnal; metabolism; oscillation