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Diatom microalgae have great industrial potential as next-generation sources of biomaterials and biofuels. Effective scale-up of their production can be pursued by enhancing the efficiency of their photosynthetic process in a way that increases the solar-to-biomass conversion yield. A proof-of-concept demonstration is given of the possibility of enhancing the light absorption of algae and increasing their efficiency in photosynthesis by in vivo incorporation of an organic dye which acts as an antenna and enhances cell growth and biomass without resorting to genetic modification. A molecular dye (Cy5) is incorporated in Thalassiosira weissflogii diatom cells by simply adding it to the culture medium and thus filling the orange gap that limits their absorption of sunlight. Cy5 enhances diatoms’ photosynthetic oxygen production and cell density by 49% and 40%, respectively. Cy5 incorporation also increases by 12% the algal lipid free fatty acid (FFA) production versus the pristine cell culture, thus representing a suitable strategy to enhance biofuel generation from algal species. Time-resolved spectroscopy reveals Förster Resonance Energy Transfer (FRET) from Cy5 to algal chlorophyll. The present approach lays the basis for non-genetic tailoring of diatoms’ spectral response to light harvesting, opening up new ways for their industrial valorization

Additional file 1: Table S1. Coverage obtained by Illumina sequencing for WT and e8 mutant strain. Table S2. Mutation identified on gene coding for proteins putatively located in the chloroplast. Prediction of chloroplast transit peptide was performed with Hectar software. Figure S1. Mutants screening by 680/730 nm absorption ratio. Absorption ratio 680/730 nm was used to assay the chlorophylls per cell content. Only colonies with a reduction of at least 25% was selected for further analyses. Error bars are reported as standard deviation (n=3). Figure S2. Light dependent zeaxanthin accumulation in WT and e8. Samples were illuminated for 1 h with a strong light (2500 μmol photons m-2 s-1). Pigments composition was evaluated at different time points by DMSO extraction and HPLC analysis. (A) Depoxidation index calculated as (zea + anthera/2)/(anthera+viola+zea). (B) Zeaxanthin per carotenoid content. (C) Zeaxanthin per chlorophyll content. Errors are reported as standard deviation, significantly different values are marked with * if p 0.1 at the different time points. Figure S4. Biomass and lipid productivity of WT and e8 mutant at different irradiances. (A)) Maximum daily productivity in terms of gr L-1 day-1. (B, C) Nile red fluorescence of WT and e8 mutant normalized to dry weight (B) or to the culture volume (C). (D) Fold change of Nile red fluorescence and biomass dry weight on a volumetric base in e8 mutant compared to WT. Errors are reported as standard deviation, significantly different values are marked with * if p

Additional file 1: Table S1. Coverage obtained by Illumina sequencing for WT and e8 mutant strain. Table S2. Mutation identified on gene coding for proteins putatively located in the chloroplast. Prediction of chloroplast transit peptide was performed with Hectar software. Figure S1. Mutants screening by 680/730 nm absorption ratio. Absorption ratio 680/730 nm was used to assay the chlorophylls per cell content. Only colonies with a reduction of at least 25% was selected for further analyses. Error bars are reported as standard deviation (n=3). Figure S2. Light dependent zeaxanthin accumulation in WT and e8. Samples were illuminated for 1 h with a strong light (2500 μmol photons m-2 s-1). Pigments composition was evaluated at different time points by DMSO extraction and HPLC analysis. (A) Depoxidation index calculated as (zea + anthera/2)/(anthera+viola+zea). (B) Zeaxanthin per carotenoid content. (C) Zeaxanthin per chlorophyll content. Errors are reported as standard deviation, significantly different values are marked with * if p 0.1 at the different time points. Figure S4. Biomass and lipid productivity of WT and e8 mutant at different irradiances. (A)) Maximum daily productivity in terms of gr L-1 day-1. (B, C) Nile red fluorescence of WT and e8 mutant normalized to dry weight (B) or to the culture volume (C). (D) Fold change of Nile red fluorescence and biomass dry weight on a volumetric base in e8 mutant compared to WT. Errors are reported as standard deviation, significantly different values are marked with * if p