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Photobiological Hydrogen Production Using Bioengineered Algae Outline • • • • • Advantages to a Hydrogen Fuel Economy Green Algae Limitations of the Algae Cell Physiology and Two-Stage Photosynthesis of H2 Production with Green Algae Possible Solutions to Current Limitations of H2 Production Provided by Biotechnology • The Future Why Hydrogen? • • • • Highest energy/mass density of all known fuel types Produced Domestically Sustainable (if produced from water) Environmentally Friendly • Fuel Cell: No pollutants or greenhouse gases • ICE: only (NOx) Chlamydomonas reinhardtii • Single-celled green Algae • 1939: German researcher Hans Gaffron discovered hydrogen metabolism • Hydrogenase Catalyzed reaction, active only in absence of oxygen H2 Production Limitations of the Algae Cell • Low light conversion effiency (~10%) • Oxygen production inhibits Fe-hydrogenase • Has not yet been overcome after 60 years of research A hydrogen-producing C. reinhardtii culture. Two Possible H2 Production Pathways • Photosystem II • Oxidation of Indegenous Cellular Substrate Hydrogenase-related electron transport pathways in green algae. Two-stage photosynthesis H2 Production • Lack of Sulfur: reversible decline in rate of oxygenic photosynthesis, no affect to rate of mitochondrial respiration. Immediately elicited H2 Production. • Circumvents sensitivity of Fe-hydrogenase to oxygen through temporal separation of oxygen and H2 photoproduction H2 Production by S deprivation Involves Coordinated Interaction Between • Oxygenic photosynthesis: e- transported through e- transport chain to Fehydrogenase • Mitochondrial respiration scavenges oxygen gen. by photosynthesis • Endegenous substrate catabolism yields suitable substrate for oxidative phosphorylation in mitochondria • Release of H2 gas provides baseline levels of photosynthesis Coordinated photosynthetic and respiratory electron transport and coupled phosphorylation during H2 production. Regulation of Hydrogenase • Grown under photo-autotrphopic condions algae neither consume or produce hydrogen • Fe hydrogenase gene induced upon incubation of cells under anaerobic conditions in the dark, or S deprivation • Results suggest oxygen is a positive suppresser of Fe hydrogenase gene expression at transcriptional level Possible Solutions to Current Limitations • Low light conversion efficiency: Truncate chlorophyll antenna size of PS-II using RNAi method • Availability of reduced Ferrodoxin for Fe-Hydrogenase: Change Ferrodoxin affinity for (FNR) without affecting Fe-hydrogenase interaction The Future http://www.toyota.com/fuelcell/
