Cyclic appearance of aerobic nitrogenase activity during synchronous growth of unicellular cyanobacteria

The aerobic synchronous growth of marine unicellular cyanobacteriaSynechococcus spp., with molecular nitrogen as the sole nitrogen growth nutrient source, was experimentally demonstrated. Cell division synchrony was induced by withholding aeration and illumination for 20 h. Three distinct cell division cycles of approximately 20 h each were observed. During the first cell division cycle, high degrees of synchrony of 78%–86% were observed in the series of cultures studied. The aerobic nitrogenase activity appeared shortly while the cell division was completed and the cell size was still small, and it disappeared after the cells were enlarging photosynthetically. Thus, three distinct cycles in aerobic nitrogenase activity were also observed having approximately the same 20-h interval as the cell division cycle. The peak aerobic nitrogenase activity was determined to be as high as 840–1220 nmol C₂H₂ reduced per milligram dry weight per hour.