Author(s): Brecken Shakespeare, Colton Koch
Mentor(s): Jacob Dean
Institution SUU
Spirulina is a genus of photosynthetic cyanobacteria containing phycocyanin, a light-capturing protein crucial for photosynthesis. This cyanobacteria evolved to optimize effective energy transfer in the yellow-red region (550-650nm) which is then used to help these cyanobacteria photosynthesize and provide the needed energy to sustain life. In recent years, secondary pigments have been introduced to multiple light harvesting units, in an attempt to alter, and potentially aid, these natural proteins’ light harvesting capabilities. This can be accomplished through carefully selecting a pigment that will harvest light at a different wavelength, so as to increase the energy being obtained from light, yet also has an energy and structure that would be optimal for energy transfer to the native pigments. The optimal candidate, Rhodamine B, seeing as it has a large absorbance at 555 nm and fluorescence at 618 nm, which also makes it exceptionally compatible for energy transfer to a phycocyanin acceptor which absorbs at 622 nm. To test the light-harvesting properties of the modified solution, we took dilute solutions with similar absorbances of phycocyanin, rhodamine-B, and a mixture, and collected UV-vis and fluorescence spectra of each. The spectra were analyzed to study how the secondary pigment rhodamine-B affected the light-harvesting properties of phycocyanin and its energy transfer. We found that a spectral comparison is highly sensitive to concentration (and concentration differences), yet the presence of rhodamine-B enhances the overall fluorescence of the phycocyanin protein at lower concentrations. The analysis developed herein provides a protocol for careful comparison of a donor-acceptor mixture.