Abstract
Cyanobacterial phycobilisome (PBS) pigment-protein complexes harvest light and transfer the energy to reaction centers. Previous ensemble studies have shown that cyanobacteria respond to changes in nutrient availability by modifying the structure of PBS complexes, but this process has not been visualized for individual pigments at the single-cell level due to spectral overlap. We characterized the response of four key photosynthetic pigments to nitrogen depletion and repletion at the subcellular level in individual, live Synechocystis sp. PCC 6803 cells using hyperspectral confocal fluorescence microscopy and multivariate image analysis. Our results revealed that PBS degradation and re-synthesis comprise a rapid response to nitrogen fluctuations, with coordinated populations of cells undergoing pigment modifications. Chlorophyll fluorescence originating from photosystem I and II decreased during nitrogen starvation, but no alteration in subcellular chlorophyll localization was found. We observed differential rod and core pigment responses to nitrogen deprivation, suggesting that PBS complexes undergo a stepwise degradation process.
Highlights
Present AddressKeywords Cyanobacteria · Photosynthesis · Phycobilisome · Nitrogen · Hyperspectral confocal fluorescence microscopy · Multivariate analysis
Cyanobacteria are unicellular photosynthetic microbes that played a central role in oxygenating the Earth’s early atmosphere (Buick 2008)
Synechocystis 6803 cells were starved of nitrogen and samples were collected at 0, 24, and 48-h time points, and at 24 h after nitrogen readdition (Fig. 1a)
Summary
Keywords Cyanobacteria · Photosynthesis · Phycobilisome · Nitrogen · Hyperspectral confocal fluorescence microscopy · Multivariate analysis
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