Cellular differentiation and nitrogenase activity in the cyanobacteriumAnabaena

Nitrogenase activity at periods of differentiation of heterocysts and akinetes was assayed by the acetylene reduction technique. There was no nitrogenase activity in ammoniumgrown, non-heterocystousAnabaena sp.; the activity appeared only after a lag-phase of about 17 – 21 h after the ammonium-grown culture had been transferred to medium free of combined nitrogen. This activity started appearing as the proheterocysts were developing to mature heterocysts. Maximum nitrogenase activity was attained with exponential phase of culture and mature heterocysts. This activity gradually decreased with the differentiation of akinetes. Only insignificant nitrogenase activity was observed in old cultures in which most cells had matured into akinetes.