Fermentative metabolism to produce hydrogen gas and organic compounds in a cyanobacterium, Spirulina platensis

The non nitrogen-fixing and filamentous cyanobacterium Spirulina platensis NIES-46 produced hydrogen gas, ethanol, and low molecular organic acids auto-fermentatively under dark and anaerobic conditions. The fermentative productivity was enhanced by incubating the cyanobacterium under nitrogen-starved conditions. Cell-free extracts of the cyanobacterium catalyzed hydrogen production by the addition of acetyl-coenzyme A and pyruvate. Pyruvate-degrading and acetaldehyde dehydrogenase activities were observed in the cell-free extracts. These results suggest that the fermentation was dependent on the anaerobic degradation of endogenous glycogen via pyruvate.