Analysis of Synechococcus pigment types in the sea using single and dual beam flow cytometry

Abstract

Listen

Translate article

Distributions and optical properties of Synechococcus cells were studied at sea using flow cytometric techniques to distinguish between several different pigment types. Cells with only phycoerythrobilin chromophores were distinguished from those with both phycoerythrobilin and phycourobilin (PUB) chromophores by exciting with 488 nm light and measuring the resulting phycoerythrin fluorescence below 560 nm (green) and above 560 nm (orange). All populations detected had green/orange emission ratios similar to PUB-containing strains of Synechococcus in culture. In addition, the ratio of fluorescence emission intensity resulting from excitation at 488 and 515 nm was used to measure the relative PUB content of the cells. In the majority of samples, we found ratios as high or higher than those of the cultured strains considered to have unusually high PUB contents. These findings suggest that our perception of the characteristics of Synechococcus populations in the open ocean may have been biased by studies of cells from culture collections. According to our survey, virtually all Synechococcus cells in the open ocean contain PUB and most of them have very high relative PUB contents. This gives them absorption properties not very different from those of the eukaryotic phytoplankton, and this could explain why photosynthetic action spectra have suggested that light absorption by phycoerythrobilin-rich phycoerythrin (at about 550 nm) is relatively unimportant in the open ocean.