Microalgae are primitive microscopic plants living in aqueous
environments. Cyanobacteria, formerly known as blue-green algae, are now
recognized as bacteria since the anatomical characteristics of their cells are
prokaryotic (bacterial type). Miroalgae and Cyanobacteria along with higher
plants, are capable of oxygenic photosynthesis according to the following
CO2 + H2O ® 6 [CH2O] + O2.
Photosynthesis consists of two processes: light energy
conversion to biochemical energy by a photochemical reaction, and CO2
reduction to organic compounds such as sugar phosphates, through the use of this
biochemical energy by Calvin-cycle enzymes. Under certain conditions, however,
instead of reducing CO2, a few groups of microalgae and
Cyanobacteria consume biochemical energy to produce molecular hydrogen (Fig.
5-2; 5-3). Hydrogenase and nitrogenase enzymes are both capable of hydrogen