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 Production with Green Algae

• Possible Solutions to Current Limitations of 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

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 Production Pathways

• Photosystem II

• Oxidation of Indegenous Cellular Substrate

Hydrogenase-related electron transport pathways in green algae.

Two-stage photosynthesis Production

• Lack of Sulfur: reversible decline in rate of oxygenic photosynthesis, no affect to rate of mitochondrial respiration. Immediately elicited Production.

• Circumvents sensitivity of Fe-hydrogenase to oxygen through temporal separation of oxygen and photoproduction

Production by S deprivation Involves Coordinated Interaction Between

• Oxygenic photosynthesis: e- transported through e- transport chain to Fe-hydrogenase

• Mitochondrial respiration scavenges oxygen gen. by photosynthesis

• Endegenous substrate catabolism yields suitable substrate for oxidative phosphorylation in mitochondria

• Release of 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/