Period doubling observed in the circadian photosynthetic rhythm of the prokaryotic cyanobacterium Cyanothece RF-1

The circadian rhythm is an endogenous biological clock that governs biochemical phenomena or behavior in organisms. The Cyanothece RF-1 is the first prokaryote shown to exhibit circadian nitrogen-fixing rhythm. The observation of the circadian photosynthetic rhythm of this strain was recently reported by the authors. In this work, the dissolved-oxygen variation in the culture of Cyanothece RF-1 was recorded, which would reveal the photosynthetic activity of the strain. For a culture of about 1x10$^{8}$ cells/ml in concentration, a period-doubling pattern was clearly displayed in the circadian photosynthetic rhythm signals. The mechanism corresponding to this nonlinear effect will be discussed. These results represent the first observation of the period doubling in the circadian rhythm of a prokaryotic cyanobacterium.