Oral Presentation 2014 International Biophysics Congress

Solar energy conversion efficiencies in photosynthesis: Minimizing the chlorophyll antennae to maximize efficiency (#156)

Anastasios Melis 1
  1. University of California, Berkeley, CA, USA

A genetic tendency of photosynthetic organisms to assemble large arrays of light-absorbing chlorophyll antenna molecules in their photosynthetic apparatus is a survival strategy and a competitive advantage in the wild, where light is often limiting. Competition and survival in the wild requires capturing more light for self, even if in excess of what is needed to saturate photosynthesis and eventually wasted, and preventing light capture by competing neighbors. This competitive survival strategy is detrimental to production-type monocultures under bright sunlight, where over-absorption of photons at the surface of the culture or canopy, and wasteful dissipation of the excess absorbed energy, are undesirable.  Under bright sunlight, more than 80% of absorbed photons can thus be wasted, reducing photon use efficiencies and photosynthetic productivity to undesirably low levels. The present work examines the theoretical maximum of solar energy conversion efficiency and productivity in photosynthetic systems. This will be contrasted with actual measurements of substantially lower efficiencies in a variety of photosynthetic organisms, including cyanobacteria, green microalgae, C3 and C4 plants. Engineering of Truncated Light-harvesting chlorophyll Antenna size (TLA) strains, where the number of chlorophyll molecules in the photosynthetic apparatus is genetically limited, in all classes of photosynthetic organisms, helps to alleviate excess absorption of sunlight and the ensuing wasteful dissipation of excitation energy, and to maximize solar-to-product energy conversion efficiency and photosynthetic productivity in high-density mass cultivations of microalgae and crop plants. Minimizing, or truncating, the chlorophyll antenna size of the photosystems is a strategy that mitigates over-absorption and surface saturation of photosynthesis and substantially improves sunlight penetration and overall culture or canopy solar energy conversion efficiency and productivity up to 300%. The TLA concept is beginning to find application in the commercial exploitation of microalgae and crop plants for the generation of biomass, fuel, synthetic chemistry, and pharmaceutical feedstock.