THE IMPACT OF TERRIGENOUS IRON GRADIENTS ON CHROMATIC ACCLIMATION OF MARINE CYANOBACTERIA

Synechococcus spp., a picocyanobacteria, is one of the most abundant and ubiquitous phytoplankton in the world’s oceans. They are found in a variety of oceanic environments including turbid, optically clear, nutrient rich, and oligotrophic waters. Some strains undergo chromatic acclimation (CA), a process whereby photosynthetic pigments are optimized to harvest ambient wavelengths of light. This optimization is observed as a change in the relative expression of chromophores of the accessory pigment phycoerythrin: cyan-absorbing phycourobilin (PUB); and green-absorbing phycoerythrobilin (PEB). The PUB:PEB range is 1.2-1.4 in blue LED light and decreases to 0.3-0.5 in green or white LED light. Our lab experiments reveal that available dissolved iron (Fe’) concentrations, independent of light color, trigger small changes in protein expression and PUB:PEB within some Synechococcus chromatic adapters. Iron replete conditions (>1nM Fe’) produce lower PUB:PEB while iron starved conditions (<0.1nM Fe’) increases PUB:PEB. This has been observed in the chromatic adapter strains WH 8020 and RCC 2673. Optimization for blue light-harvesting (higher PUB:PEB) at low iron concentrations could indicate that trace elements, as well as light color, are triggers for light acclimation responses for cyanobacteria in the ocean.