Intracellular Spectral Recompositioning of Light Increases Photosynthetic Efficiency and Reduces Light Associated Stress in a Versatile Model Diatom

Diatoms as photosynthetic cell factories can provide the means to reach a sustainable production of petrochemical and bioactive compounds; however, a requisite to achieve this goal is to increase the species photosynthetic efficiency, which generally remains less than five percent. We have developed and implemented a strategy, herein referred to as Intracellular Spectral Recompositioning of light (or ISR), which through absorption of excess blue light and its intracellular emission in green spectral band, may improve light utilization. We demonstrate that ISR can be employed chemogenically, through use of lipophilic fluorophores, or biogenically, through expression of an enhanced green fluorescent protein (eGFP) in the model diatom Phaeodactylum tricornutum. Engineered P. tricornutum cells expressing eGFP achieved twenty-eight percent higher efficiency in photosynthesis than the parental strain under mixed red and blue light condition. Further, pond simulator experiments demonstrated that eGFP transformants could outperform their wild type parental strain by fifty percent in biomass production rate under high intensity white LED illumination. Transcriptome analysis of the engineered strain identified up-regulation of genes, such as the Light Harvesting Complex Protein X (LHCX) genes including LHCX1, LHCX3, and LHCX4, that associated with photosynthesis, along with down regulation of non-photochemical quenching (NPQ) genes and those involved in response to light stress. The developed ISR approach is applicable toward improving cultivation of diatomaceous production strains under high light intensity cultivation in indoor reactors, or in open outdoor ponds.