Abstract
The unicellular cyanobacterium Gloeothece sp. PCC 6909 was grown diazotrophically in continuous culture. Various light-dark regimes and dilution rates were applied. Nitrogenase activity (acetylene reduction), oxygen-production and -consumption, and glycogen were measured over 24 h periods covering one complete light-dark cycle. Gloeothece fixed nitrogen predominantly in the light, concomitant with photosynthetic oxygen evolution. This result was found irrespective of the imposed light-dark regime or dilution rate. It is concluded that temporal separation of photosynthesis and nitrogen fixation is not obligatory in Gloeothece.