PARENT SESSION
Posters P5D Emerging techniques and systems. Abstracts (731-741)

Genetic improvements for increasing solar energy conversion efficiency by microalgae cultures. Juergen Polle^*,1, Munevver Aksoy¹, Joseph Weissman³, John Benemann³, ¹ Department of Biology, Brooklyn, NY, USA³ SeaAg, Inc., Vero Beach, FL, USA

ABSTRACT- Dense microalgal mass cultures and higher plant canopies exhibit suboptimal productivities because of the light saturation effect. On average, an algal cell in a mass culture pond or a plant cell in a high leaf area index canopy experiences low light intensities. In response it assembles large numbers of chlorophyll (Chl) molecules into arrays of light-harvesting or antenna chlorophylls and other pigments, to harvest as many photons as possible. However, this results in cells near the culture surface exposed to full sunlight to absorb photons greatly in excess of what can be processed by the photosynthetic apparatus, with the excess captured photons degraded to heat or fluorescence. For microalgae mass cultures in full sunlight, the overall wastage is 70 to 80% of photons absorbed, reducing biomass productivities proportionally. Moreover, such excessive but ineffective photon absorption damages the photosynthetic apparatus (photoinhibition), further reducing solar conversion efficiencies and, thus, biomass productivities. To overcome these shortcomings, we have developed mutants of microalgae strains of Cyclotella (diatom) and Tetraselmis (green alga) used in commercial mass cultivation with a truncated number of antenna Chls in the photosystems, to test the prediction of higher solar energy conversion efficiencies and confirm prior results using laboratory adapted strains (Polle et al., J. Int. Hyd. Res. 27:1257-1264, 2002). Initial results with outdoor cultures demonstrate the feasibility of cultivating such mutant strains in mass culture, but high reversion rates limit their utility. Deletion mutations are being developed to overcome this problem and allow achievement of sustained high productivities with such strains. Using this approach we predict that maximal solar energy conversion efficiencies into microalgal biomass could be increased two to three-fold from current levels, allowing for greatly expanded applications of microalgae mass cultures, including to agricultural commodities and hydrogen production. This research also has applications to increasing crop productivity.

KEY WORDS: photosynthesis improvement, productivity, algae, light saturation