ABSTRACT
This chapter reviews the diversity, function, and physiological roles of Hydrogen (H2)-producing enzymes. It addresses the principles and results of various approaches by which cyanobacterial and microalgal metabolisms were oriented toward a continuous photoproduction of H2. The chapter discusses some tracks for future improvements of H2 photoproduction by green microalgae. Hydrogenases are widely spread among the microorganisms' diversity with numerous representatives in the domain of bacteria and archaea, and are also present in some unicellular eukaryotic organisms. Biodiversity of [FeFe]-hydrogenases is poor compared with that of [NiFe]-hydrogenases. These enzymes are present in anaerobic prokaryotes, but also in a few lower eukaryotes, such as anaerobic fungi, parasitic protozoas, and unicellular microalgae. Nitrogenases catalyze the reduction of molecular nitrogen N2 into ammonium (NH3) in diazotrophic bacteria. C. reinhardtii is widely regarded as a model organism for bioenergetics studies on mitochondrial respiration and photosynthesis due to the availability of genetic and molecular tools.
