Hydrogen photoproduction by Azolla and Anabaena azollae

Photoproduction of hydrogen by the aquatic fern Azolla and its phycobiont Anabaena azollae was analyzed for its efficiency, stability, and longevity. Fronds of Azolla filiculoides produced hydrogen in the light, when incubated under N₂ atmosphere, or air, in the presence of carbon monoxide and acetylene as inhibitors of uptake hydrogenase. Rates of H₂ photoproduction were low in comparison to the rates of acetylene reduction by Azolla fronds tested under similar conditions. It is suggested that the uptake hydrogenase was not completely inhibited, and a better solution should be developed to block H₂ uptake in the system and improve H₂ photoproduction. H₂ photoproduction by the isolated phycobiont Anabaena azollae was carried out continuously for a few days and was enhanced in the presence of argon replacing air in the gas phase. H₂ uptake activity, controlled by CO and C₂H₂ in the batch culture system, was not completely inhibited during the time course of the experiment. Batch cultures of A. azollae also have a limited efficiency and may be more effective when tested in a controlled continuous mode, providing CO₂, CO, and C₂H₂ at constant concentrations and removing photoproduced hydrogen, oxygen, and ethylene.