Discrimination of Two Phycoerythrin-Pigment Types of Synechococcus and Their Seasonal Succession in the Uwa Sea

Abstract

We identified phycoerythrin-pigment phenotypes of Synechococcus strains in samples obtained from the Uwa Sea, and investigated the seasonal changes in the pigment-type composition of the Synechococcus community in this sea from January 2001 to March 2002. Two Synechococcus strains (UT01 and UT02) with different flow cytometric signatures were isolated by sorting and subsequent culturing. Excitation spectra showed that these two strains possessed different ratios of phycourobilin (PUB) to phycoerythrobilin (PEB). Flow cytometric signatures of the two types were also different; UT01 showed a higher green to red fluorescence ratio than UT02. The ranges of green to red fluorescence intensity of the strains did not overlap, though the strains were cultured under various light intensities (7-160 μE m^-2 s^-1). In seawater samples, we could divide Synechococcus into lower-and higher-PUB types based on the ratio. There were two peaks of total Synechococcus abundance in June (2.8×10⁵ cells ml^-1) and August (1.6×10⁵ cells ml^-1) in the upper layer at a depth of 0 to 15 m. Major types during these two peaks were different; the higher-PUB type contributed 75.6% to the total Synechococcus community in June, and the lower-PUB type, 58.6% in August. This is the first report which describes the seasonal succession of two phycoerythrin-pigment types of Synechococcus in a coastal sea.