Variation in Color Acclimation Times: Part of Parameterizing a Light Color Competition Model for Cyanobacteria in Blue-Green Ocean Niches

Raisha Lovindeer, University of California, Irvine, Earth System Science, Irvine, CA, United States, Katherine Mackey, University of California Irvine, Department of Earth System Science, Irvine, CA, United States and Hannah M. Medina, University of California Irvine, Earth System Science, Irvine, CA, United States
Abstract:
Light is a limiting resource in the ocean, and light spectrum changes with depth, creating distinct light color niches. The ability of some cyanobacteria to change light harvesting accessory pigments to the complementary color of incoming irradiance (complementary chromatic acclimation, CCA) has proved a competitive advantage in models of competition for green and red light by Stomp & coworkers (2007; 2008). However this advantage is highly tied to the timing of acclimation. Here we parameterize and test this competition model for finer gradients of blue-green light niches, using Synechococcus strains that chromatically acclimate by tuning the chromophores phycourobilin (PUB) and phycoerythrobilin (PEB) of their light-harvesting accessory pigment, phycoerythrin (PE, CA4). Monoculture experiments at low light to parameterize the model reveal varying acclimation times among strains, with four of six strains acclimating 14-44% faster to blue than green or white light. Three strains displayed 3-day lag times before initiating acclimation to green light, with no lags before acclimation to blue light. Synechococcus WH8109, previously reported to display no range of chromatic acclimation despite possessing the genes of other acclimaters, showed a full range of acclimation (PUB:PEB of ~0.8 in green light and ~1.9 in blue light) and acclimated 30% faster to green than blue light. We hypothesize that acclimating strains will be better competitors than specialist strains in fluctuating light color environments when the timescale of fluctuation is longer than the timescale of acclimation. This has implications for the distribution of chromatically acclimating strains in the global ocean. The variations in acclimation times, and direction, observed for Synechococcus strains adds to our appreciation of the plethora of strategies employed within the genus to maintain ubiquity throughout the global ocean.
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