Engineering the Marine Diatom Phaeodactylum Tricornutum through Intracellular Spectral Recompositioning of Light for Developing Photosynthetic Cell Factories

Engineering the marine diatom Phaeodactylum tricornutum through intracellular spectral recompositioning of light for developing photosynthetic cell factories

Weiqi Fu^1,2, Gilbert Yeoh Tan¹, Mehar Sultana¹, Kourosh Salehi-Ashtiani¹

¹Division of Science and Math, and Center for Genomics and Systems Biology (CGSB), New York University Abu Dhabi, P.O. Box 129188, Abu Dhabi, UAE

²Center for Systems Biology and Faculty of Industrial Engineering, Mechanical Engineering and Computer Science, School of Engineering and Natural Sciences, University of Iceland, Reykjavik 101, Iceland

Diatoms are a major group of algae in the phytoplankton communities and can be found in waters worldwide wherever sufficient nutrients and lights are present. Marine diatoms, such as Phaeodactylum tricornutum, can accumulate high levels of lipids and have the potential to be engineered as cell factories for sustainable bio-based industries. They are expected to be a promising resource for future clean energy supply and sustainable production of bioactive compounds such as value-added nutraceuticals and active pharmaceutical ingredients. Light energy conversion efficiency is a decisive factor in diatom-based cell factories for determining their economical feasibility. 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 in photobioreactors (PBRs). We hypothesized and show here that Intracellular Spectral Recompositioning of light (or ISR) can increase the quantum yield of photosynthesis if the otherwise wasted portion of blue light is shifted to green which diatoms have evolved to harvest through accessory photosynthetic pigments. We show that an addition of 2 µM of BODIPY fluorescent dye increases the photosynthetic efficiency from 4.9±1.0 % to 7.5±1.2 % in high-density P. tricornutum cultures under combined red and blue light-emitting diode illumination in flat panel PBRs over a 24-hr period. To biogenically implement ISR, fluorescent proteins were elected with high quantum yield, photostability and extinction coefficient, and heterologously expressed in P. tricornutum cells. Transformants were selected and quantitatively screened using fluorescence-activated cell sorting (or FACS) for high expression of fluorescent proteins with an increase of 100 folds in green fluorescence intensity. Preliminary results indicated that transformant P. tricornutum cells exhibited an average growth rate of 1.3 times of their wild type counterpart under light stress conditions. Our experiments demonstrate that ISR can be employed to improve photosynthetic efficiency of the diatom P. tricornutum in PBRs. Further studies on transformants expressing fluorescent proteins are in progress for optimizing biomass productivity as well as photosynthetic efficiency. This study may also provide a method to minimize cell damage and enhance cell tolerance to light stress under photosynthetically active radiation (or PAR) conditions.