Characterization of hydrogen production by the co-culture of dark-fermentative and photosynthetic bacteria

Apprehension over exhaustion of fossil fuels and global warming, due to increasing amounts of CO₂, has generated a lot of attention for the subject of renewable energy. Renewable energy has an intermittency problem and its output fluctuates depending on natural conditions. Biohydrogen is one of the promising renewable energy sources. Hydrogen produced by photosynthetic bacteria depends on the intensity of light irradiation and also fluctuates with the daily variation of sunlight. The co-culture system of dark-fermentative and photosynthetic bacteria is one solution for reducing the dependency of hydrogen production on light intensity. Because these two strains of bacteria have different processes of hydrogen production, it is possible to combine different outputs so far as the co-culture system works well. This study performed hydrogen production by the co-culture system composed of agar gels embedded with both dark-fermentative bacteria, Clostridium butyricum MIYAIRI, and photosynthetic bacteria, Rhodobacter sphaeroides RV, under a fluctuating light-irradiation. The time-course of hydrogen production was determined for the different conditions of co-culture in the mixing ratios of the two bacterial strains and light-irradiation patterns. As a result, the co-culture system succeeded in producing hydrogen exceeding that in the case of a single culture system and improved its stability against light fluctuation. Hydrogen production by the co-culture system would be applicable to the reduction of intermittency in renewable energies.