Intracellular Spectral Recompositioning of Light for Improving Photosynthetic Efficiency in the Marine Diatom Phaeodactylum Tricornutum

Intracellular spectral recompositioning of light for improving photosynthetic efficiency in the marine diatom Phaeodactylum tricornutum

Weiqi Fu and Kourosh Salehi-Ashtiani*
Division of Science and Math, and Center for Genomics and Systems Biology
(CGSB), New York University Abu Dhabi, P.O. Box 129188, Abu Dhabi, UAE

*Corresponding author

Marine diatoms that usually accumulate high amounts of lipids generate as much as
40% of total organic carbon produced each year in the sea. Marine diatoms are expected to be a promising resource for future clean energy supply, as well as for sustainable production of bioactive compounds such as high value nutraceuticals and active pharmaceutical ingredients. The light energy conversion efficiency is a decisive factor in intensive cultivation of diatoms in photobioreactors (PBRs) for determining the economical feasibility and limits of diatom-based cell factories and relevant industrial applications. Maximizing the photosynthetic efficiency may significantly improve biomass productivity and reduce the overall direct and indirect energy costs while imposing high-intensity illumination on algal cultures. We hypothesized and show here that Intracellular Spectral Recompositioning of light (or ISR) can increase the quantum yield of light if the otherwise wasted portion of blue light spectrum is shifted to green which diatoms have evolved to harvest through accessory photosynthetic pigments. We demonstrate that ISR can be employed to largely improve photosynthetic efficiency of the diatom Phaeodactylum tricornutum in flat- panel PBRs. We show that an addition of 2 µM of BODIPY fluorescent dye increased the photosynthetic efficiency from 4.9±1.0 % to 7.5±1.2 % in high-density culture of P. tricornutum under combined red and blue light-emitting diode illumination, on the basis of cell growth rate over a 24-hr period. To biogenically implement ISR, green fluorescent proteins (GFPs) as well as other FPs were elected with high quantum yield, photostability and extinction coefficient, and heterologously expressed in P. tricornutum cells. Transformants were pooled and then quantitatively screened using fluorescence-activated cell sorting (or FACS) for high expression of fluorescent
proteins. Evaluation of transformant P. tricornutum cells is in progress and it is expected to optimize both intracellular and intercellular light delivery and re- distribution in flat-panel PBRs through integrating selected fluorescent proteins into the existing light harvesting complexes. The carotenoid metabolism in transformants and cell tolerance to light stress will also be studied for optimizing biomass productivity as well as photosynthetic efficiency. This study may also provide a method to minimize cell damage caused by light stress of photosynthetically active radiation.