Conversion of algal biomass to hydrogen by marine bacterial consortia

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Among the many global environmental problems facing society today, greenhouse warming is widely recognized as one of the most serious.To address this problem, CO_2 fixation by microalgae is considered as an environmentally friendly, energy-saving measure.However, microalgal systems produce large amounts of waste biomass which would easily revert to CO_2.In this study, we attemped to develop a system in which starch accumulated in C0_2-fixing algal biomass is biologically converted to H_2, one of the most promising future energy mediai) A halotolerant bacterial consortium, which could directly convert starch to H_2, was selected from an activated sludge of a night soil treatment plant having a seawater dilution system.The consortia showed a strong ability to convert raw starch to H_2 in the presence of 3% sodium chloride.ii) Two different bacterial strains, which played roles in starch degradation and H_2 production from the degraded products, respectively, were isolated from the consortium and identified.iii) A pure mixed culture of known lactobacillus and photosynthetic bacterium showed more efficient conversion of raw starch to H_2 compared with the above bacterial consortium.iv) The pure mixed culture could produce H_2 from the algal starch accumulated in freshwater or marine green algae with high conversion yields and rates.We could demonstrate that C0_2-fixing algal biomass can be directly converted to H_2 by using bacterial consortium or mixed culture.This system will have the advantages of energy efficiency and simplicity compared with other biological conversion systems previously reported.