 In the late 1990s Anastasios Melis discovered that deprivation of sulfur induces the alga to switch from the production of oxygen (normal photosynthesis) to the production of hydrogen.He found that the enzyme responsible for this reaction is hydrogenase, but that the hydrogenase lost this function in the presence of oxygen.Melis also discovered that depleting the amount of sulfur available to the algae interrupted their internal oxygen flow, allowing the hydrogenase an environment in which it can react, causing the algae to produce hydrogen.