Photosynthetic Diatoms inhabit various aquatic systems. The fucoxanthin chlorophyll a/c binding protein (FCP) is a unique light-harvesting antenna complex in diatoms that is highly capable of absorbing blue-green light. These antennas move excitations via consecutive downhill energy transfers to photosystem cores, where charge separation leads to photosynthetic reactions. Preliminary results show subtle differences in energy transfer between the coastal and oceanic strains of the diatom Phaeodactylum tricornutum grown under high white light. Due to varying irradiance qualities in coastal and oceanic habitats, we hypothesized that diatoms sampled from such locations would present differences in their light-harvesting machinery and energy transfer pathways when grown under more stressful light conditions. In the current study, we have grown our diatoms in three different light conditions— high white light (40 µmol/m2s), low white light (20 µmol/m2s), and red-light (20 µmol/m2s). We measured pigment absorption and characterized the growth rate of each strain under different light conditions using UV-Vis spectroscopy. Time-resolved fluorescence spectroscopy was used to observe differences in energy transfer pathways and timescales. When grown under these stressors, coastal and oceanic diatom light-harvesting show more pronounced spectral differences. Under white light, both coastal and oceanic diatoms have similar growth rates. Phase contrast microscopy also reveals altered morphology in the red light incubated cells. The results of our study reveal how photosynthetic organisms can fine-tune their light-harvesting systems to better acclimate to environmental stressors.

Effect of varying irradiances on the light-harvesting of coastal and oceanic diatom Phaeodactylum tricornutum

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