Photobiological
Hydrogen Production
Using Bioengineered Algae
Outline
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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?
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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/