Cyanobacteria are the only bacteria capable of performing oxygenic photosynthesis in which they harness solar energy and convert it into chemical energy stored in carbohydrates. Under specific conditions, cyanobacteria can use solar energy to produce also molecular hydrogen.

Biodiversity among cyanobacteria for H₂ production has not been efficiently studied. Here we report the screening of 400 cyanobacterial strains isolated from the Baltic Sea and Finnish lakes for efficient H₂ producers. Approximately 50% of these strains produced detectable amounts of H₂. Ten strains produced similar or up to 4 times as much of H₂ as the hydrogenase mutants of Anabaena PCC 7120 and Nostoc punctiforme ATCC 29133 specifically engineered in different laboratories to produce higher amounts of H₂. All ten H₂ producers are N₂-fixing filamentous, heterocystous strains, seven of them are benthic and three are planktonic strains. Different culturing parameters, such as light intensity, cell density, pH and temperature had a pronounced effect on the H₂ production rates of the two good H₂ producers, Calothrix 336/3 and XPORK 5E strains. Notably, the culture conditions for optimal H₂ production varied between different cyanobacterial strains.