Phycoerythrin Signatures in the Littoral Zone

My long term goal is to understand how adaptive phenotypes evolve in marine organisms, especially marine phytoplankton. This research examines the role of the optical environment in the evolution of the light harvesting apparatus of marine picocyanobacteria, specifically those with phycoerythrin as their principal light harvesting pigment. Phycoerythrin PE refers to a family of highly fluorescent, water-soluble pigments that are the primary light harvesting pigments of many marine picocyanobacteria, a globally important group of marine phytoplankton. In marine Synechoccocus and many other picocyanobacteria, these pigments are typically organized into phycobilisomes, macromolecular structures that provide nearly all light energy for Photosystem II Glazer, 1999. Thus, the wavelengths of light that can be used for photosynthesis are determined by the spectral forms of PE the organisms synthesize. This, in turn, depends on the relative concentration of two different chromophores that can be incorporated into the PE heterodimer. These are phycoerythrobilin PEB, yamma AbsMax, 550nm, found in all PEs, and phycourobilin PUB, yamma AbsMax, 500 nm found in varying concentrations in some forms of PE. PEB provides for efficient utilization of green wavelengths of light as the relative abundance of PUB increases, the spectral signature of the PE becomes more complex i.e. additional peaks and shoulders in the fluorescence excitation and absorption spectrum. The ecological effect of increasing the PUBPEB ratio is that the cells ability to use shorter wavelengths that penetrate more transparent seawater greatly increases.