Production of H2 by the unicellular cyanobacterium Gloeocapsa alpicola CALU 743 during fermentation

The unicellular non-nitrogen-fixing cyanobacterium Gloeocapsa alpicola grown in the presence of limiting concentrations of nitrate is capable of intensive H2 production during incubation under dark anoxic conditions. This production of H2 is the result of fermentation of glycogen accumulated during photoautotrophic growth. Besides H2, acetate and CO2, small amounts of D-lactate and ethanol were found as the products of fermentation. The fermentation stoichiometry, balances and enzymes activities indicate that the main pathway for glycogen degradation in G. alpicola is carried out via energy-yielding acetate formation involving pyruvate:ferredoxin oxidoreductase and acetate kinase. It is proposed that the H2 production is realized by a hydrogenase on the stages of NAD(P)H generation. The removal of H2 evolved from the culture, fermenting at elevated temperature and optimal pH, with constant rate of argon, allows H2 production during at least 8 h at a significant rate.