CIRCADIAN-RHYTHM OF THE PROKARYOTE SYNECHOCOCCUS SP RF-1

The prokaryotic Synechococcus sp. RF-1 exhibited a nitrogen fixation circadian rhythm with characteristics remarkably similar to the circadian rhythm of eukaryotes. The rhythm had a free-running period of about 24 hours when the length of the preentrained cycle did not differ too much from 24 hours, and it was insensitive to changes in temperature from 22°C to 33°C. Because the endogenous rhythm of nitrogen fixation was not affected by a phase-shift of its previous cycles, the circadian rhythm in Synechococcus sp. RF-1 was not considered to be controlled simply by a feedback mechanism.