PNNL

Abstract

The nitrogen-fixing non-heterocystous cyanobacterium Plectonema boryanum was used as a model organism to study hydrogen generation by indirect biophotolysis in nitrogen-limited batch cultures that were continuously illuminated and sparged with argon/CO2 to maintain anaerobiosis. The highest hydrogen production rate (i.e., 0.18 mL/mg·day or 7.3 µmol/mg·day) ) was observed in cultures with an initial medium nitrate concentration of 1 mM at a light intensity of 100 µmol/m2·sec. The addition of photosystem II inhibitor DCMU did not reduce hydrogen production rates relative to unchallenged controls for 50 to 150 hours, and intracellular glycogen concentrations decreased significantly during the hydrogen generation period. The insensitivity of the hydrogen production process to DCMU is indicative of the fact that hydrogen was not derived from water splitting at photosystem II (i.e., direct biophotolysis) but rather from electrons provided by intracellular glycogen reserves (i.e., indirect biophotolysis). It was shown that hydrogen generation could be sustained for long time periods by subjecting the cultures to alternating cycles of aerobic, nitrogen-limited growth and anaerobic hydrogen production.