Oxygen-free hydrogen production by the marine cyanobacterium Phormidium valderianum BDU 20041

To circumvent the co-production of oxygen during hydrogen photoproduction, certain physico-chemical conditions were manipulated. Then, under white light (intensity 5.5 μmol photon m−2 s−1, 18 h dark/6 h light cycle); temperature 27°C; pH 7.5; salinity 25 g l−1, the marine, filamentous, non-heterocystous cyanobacterium Phormidium valderianum BDU 20041 was found to produce a maximum of 0.2 μmol hydrogen h−1 mg−1 dry wt in the gas phase without oxygen co-production; this was on a par with the maximum yield reports in the literature. To compensate for possible reduction in CO2 fixation under these conditions, when 10 m of different carbohydrates were used, those other than galactose, lactose and trehalose were found to be favourable. For continuous production of hydrogen when amino acids were added as a nitrogen source, isoleucine was found to be the least inhibitory. The organism was found to be essentially a dark hydrogen producer.