Complementary chromatic acclimation by shifts in phycobiliprotein spectral absorption in the cryptophyte Hemiselmis pacifica

Abstract

ABSTRACT: Cryptophytes are eukaryotic microalgae found in a variety of aquatic environments, from tea-colored ponds and lakes to the blue-water open ocean. To broaden the range of their spectral absorption beyond the limits of chlorophyll a, cryptophytes contain phycobiliprotein (PBP) accessory pigments. Hemiselmis pacifica contains the PBP cryptophyte-phycocyanin 577 (Cr-PC 577), which allows it to absorb green to orange wavelengths of light. Here, we characterized variability in PBP absorbance and growth rates of H. pacifica when this species was grown in nutrient-rich environments of differing spectral quality but equal light intensity. Two weeks after a shift from white to green light, H. pacifica altered the absorbance of its Cr-PC 577 to increase capture of green photons. Further, these complementary shifts were reversible when cultures were returned to the white-light environment, and the timescale of the reversal was faster than the original shift (~1 wk). Growth rates of H. pacifica in green light (0.25 d^-1) were lower than in white-light controls (0.32 d^-1), but not significantly different from cells grown in red light (0.27 d^-1). The ability to adjust quickly to changes in light quality may confer an ecological advantage to cryptophytes when their environment is affected by processes such as eutrophication, deforestation/afforestation, or browning.