 This process can bring to the production of large quantities of H2, but also of methane and organic substances.The main mechanisms that lead to the formation of hydrogen, involving different microorganisms, are nitrogen fixation and fermentation.The first one happens in some bacteria, such as heterocystous and non-heterocystous cyanobacteria, that have a specialized enzyme, the nitrogenase, which catalizes the reduction of N2 to NH4+.