Rhodomonas PE545 fluorescence is increased by glycerol

Phycobilins are photosynthetic pigments found in three ecologically important groups of algae: cyanobacteria, red algae, and cryptophytes. These compounds are covalently attached to proteins, which can be technically difficult to analyze compared with other photosynthetic pigments (e.g., chlorophylls and carotenoids). In this study, glycerol was demonstrated to uncouple PE545 (phycoerythrin 545), the phycobilin complex of Rhodomonas spp., from its role as a light-harvesting pigment: the fluorescence signal was increased 15-34 times, and ETR (electron transport rate) was no longer light-dependent at high light intensities. Glycerol induced fluorescence provided a simple and inexpensive protocol to ascertain the pool size of autofluorescent PE545 as well as total PE545 cell content in Rhodomonas. 20-30% glycerol was optimal for monitoring increased PE545 fluorescence with a stable signal for at least 1 h after glycerol addition. A substantial portion of PE545 passed through different-sized filter pads in cells with added glycerol, which suggests that glycerol may facilitate extraction of this pigment-protein complex from R. salina, a process that can be difficult under certain growth conditions. However, at high concentrations and/or after extended periods of contact, glycerol reduced recovery of PE545, suggesting destruction of the compound. In another approach, we found that PE545 can be recovered from acetone-extracted cells using low concentrations of SDS (sodium dodecyl sulfate) in low pH buffers. The finding provides samples for analyses of both chlorophylls and carotenoids in acetone and PE545 from the cell pellet. Rhodomonas spp. plays an important role in nature; hence methods presented here should help determine its natural abundance and distribution.

Automated summary

Phycobilins, photosynthetic pigments found in cyanobacteria, red algae, and cryptophytes, can be technically difficult to analyze due to their attachment to proteins. This study demonstrated that glycerol can uncouple PE545, a phycobilin complex, from its light-harvesting role, providing a simple method to determine its content in Rhodomonas. Additionally, recovery of PE545 from acetone-extracted cells using SDS in low pH buffers offers samples for analyzing chlorophylls and carotenoids.