Concomitant photoautotrophic growth and nitrogenase activity by cyanobacterium Plectonema boryanum in continuous culture

Abstract

Since the discovery that nitrogenase activity will develop in cultures of Plectonema boryanum in microaerobic conditions¹, this phenomenon has been demonstrated in numerous other non-heterocystous cyanobacteria^2–4. However, there is controversy as to whether such organisms are capable of sustained concomitant nitrogenase activity and photoautotrophic growth^2,5,6. An exogenous carbohydrate source (fructose) and strongly reducing conditions (produced by bubbling liquid cultures with a N₂/CO₂/H₂S gas mixture) have been deemed necessary for continuous logarithmic green growth and nitrogenase activity by batch cultures of Plectonema boryanum in the light. We report here sustained exponential growth and nitrogenase activity by P. boryanum in continuous culture gassed with nitrogen in the absence of further chemical reducing agents and exogenous carbohydrate sources.