Fundamentals of Dark Hydrogen Fermentations: Multiple Pathways and Enzymes

Biohydrogen production through dark fermentation could be a promising route to the generation of a renewable fuel source. Dark fermentation is attractive since its deployment would probably be based on known reactor technology, and, in a first application, could use various carbohydrate rich waste streams, followed by lignocellulosics, a vast largely untapped resource. A thorough understanding of the enzymes and pathways is involved would help develop strategies, especially metabolic engineering, for improving rates and yields of hydrogen production. Here, the various hydrogenases and their active sites and biochemistry are discussed followed by an examination of known hydrogen producing pathways.

Keywords: Hydrogen fermentation, [FeFe] hydrogenase, [NiFe] hydrogenase, Clostridium, Escherchia coli, mixed acid fermentation, syntrophic metabolism, carbohydrate degradation, ethanol-acetate cofermentation, redox balance.