Tuesday, July 26, 2011: 8:30 AM
Grand Chenier, 5th fl (Sheraton New Orleans)
High solar energy conversion efficiencies and rapid growth rates make microalgae ideal for bio-fuel production. Some of the largest losses in solar energy conversion and photosynthetic efficiency can be attributed to non-photochemical quenching and energy dissipation under full sunlight when light-harvesting and reaction center (RC) complexes are light-saturated. Under these conditions, up to 80% of absorbed photons may be dissipated rather than being utilized for chemical energy. A strategy that has been successful in optimizing photon utilization, involves reducing the size of the peripheral light-harvesting PSII antenna. This was achieved by altering levels of light-harvesting pigment, chlorophyll (Chl) b, which binds to the peripheral PSII antenna. A knockdown of the Chl b synthesis gene (Chl a oxygenase, CAO) through RNAi, yielded transgenic algae that assembled smaller peripheral PSII antennae and had increased rates of photosynthetic oxygen evolution and growth under high light. A relative increase in photoprotective pigments, zeaxanthin and lutein, was also observed in high light grown CAO-RNAi (CR) transgenics. Ultrastructural analysis of thylakoid membranes showed looser stacking in the CR lines relative to wild-type, potentially aiding repair of damaged PSIIRCs under high light.
The results of outdoor biomass trials in ponds of different depths demonstrated that small antenna strains allowed for improved light penetration through the culture column. Additionally, the greatest accumulation of algal biomass during the brighter growth periods tested was observed in the deepest ponds with algae having small antenna sizes. Currently, these strategies for improved light utilization are being transferred to strains for bio-fuel production.