ingle celled microalgae are among the most productive autotrophic organisms in nature due to their high photosynthetic efficiencies and the lack of heterotrophic tissues. Yet, photosynthetic efficiencies and areal productivities are 2 to 3-folds lower than their theoretical potential.
Over 50% of the energy losses associated with the conversion of solar energy into chemical energy during photosynthesis are attributed to kinetic constraints between the fast rate of photon capture by the light harvesting apparatus and the slower downstream rate of photosynthetic electron transfer. At full sunlight intensities, energy ﬂux from the light harvesting antennae to the reaction centers may be 100-folds greater than the overall linear electron ﬂow, resulting in the dissipation of up to 75% of the captured energy as heat or ﬂuorescence.
One possible means to couple energy capture and photosynthetic electron transfer more efﬁciently is to reduce the optical cross-section of the light harvesting antennae.
In an article recently published in the Elsevier B.V. scientific journal Algal Research, entitled “Optimization of photosynthetic light energy utilization by microalgae,” the Sayre laboratory in Los Alamos, New Mexico demonstrated that by partially reducing chlorophyll b levels in the green alga Chlamydomonas reinhardtii, they could tune the light harvesting apparatus for increased photosynthetic efficiency. The result was more than a two-fold increase in photosynthetic rate and a 30% increase in growth rate at saturating light intensities.
Unlike chlorophyll b-less mutants which lack the peripheral light harvesting antennae, transgenics with intermediate sized peripheral antennae have the advantage that they can carry out state transitions facilitating enhanced cyclic ATP synthesis and have robust zeaxanthin–violaxanthin cycles providing protection from high light levels. It is hypothesized that the large antennae size of wild-type algae and land plants offers a competitive advantage in mixed cultures due to the ability of photosynthetic organisms with large light harvesting antennae to shade competing species and to harvest light at low ﬂux densities.
This research was supported jointly by grants to Dr. Richard Sayre from the US Air Force, Office of Scientific Research-FA9550-08-1-0451 for Dr. Zoee Perrine, who was primarily responsible for engineering the transgenic algae, chlorophyll fluorescence kinetics and growth analyses as well as determination of LHC levels; and to Dr. Sayre from the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, as part of the Photosynthetic Antenna Research Center (PARC) Energy Frontier Research Center, DE-SC0001035 for Dr. Sangeeta Negi, who was primarily responsible for carotenoid analyses and analyses of state transitions.