PRODUCTION OF BIOPLASTICS AND HYDROGEN GAS BY PHOTOSYNTHETIC MICROORGANISMS

Our efforts have been aimed at the technological basis of photosynthetic-microbial pro-duction of materials and an energy carrier. We report here accumulation of poly-(3-hydroxybutyrate)(PHB), a raw material of biodegradable plastics and for production of hydrogen gas, and a renewable en-ergy carrier by photosynthetic microorganisms (tentatively defined as cyanobacteria plus photosynthetic ba-teria, in this report).A thermophilic cyanobacterium, Synechococcus sp. MA19 that accumulates PHB at more than 20%of cell dry wt under nitrogen-starved conditions was isolated and microbiologically identified. The mecha-nism of PHB accumulation was studied. A mesophilic Synechococcus PCC7942 was transformed with thegenes encoding PHB-synthesizing enzymes from Alcaligenes eutrophus. The transformant accumulated PHBunder nitrogen-starved conditions. The optimal conditions for PHB accumulation by a photosynthetic bac-terium grown on acetate were studied.Hydrogen production by photosynthetic microorganisms was studied. Cyanobacteria can produce hy-drogen gas by nitrogenase or hydrogenase. Hydrogen production mediated by native hydrogenase incyanobacteria was revealed to be in the dark anaerobic degradation of intracellular glycogen. A new sys-tem for light-dependent hydrogen production was targeted. In vitro and in vivo coupling of cyanobacterialferredoxin with a heterologous hydrogenase was shown to produce hydrogen under light conditions. A trialfor genetic trasformation of Synechococcus PCC7942 with the hydrogenase gene from Clostridum pasteuri-anum is going on. The strong hydrogen producers among photosynthetic bacteria were isolated and charac-terized. Co-culture of Rhodobacter and Clostriumdium was applied to produce hydrogen from glucose.Conversely in the case of cyanobacteria, genetic regulation of photosynthtic proteins was intended to im-prove comversion efficiency in hydogen production by the photosynthetic bacterium, Rhodobactersphaeroides RV. A mutant acquired by UV irradiation will be characterized for the mutation and for hydro-gen productivity in comparison with the wild type strain. Some basic studies to develop photobioreactorsare also introduced.