Phylogenetic and Pigment Phenotypical Diversification of Synechococcus Community in the Western Pacific Ocean

Synechococcus, a group of phylogenetically and phenotypically (pigment) diverse unicellular cyanobacteria, are important primary producers in marine environments. Here we reported the abundance, pigmentation genetic diversity, and taxonomic diversity of Synechococcus in the western Pacific Ocean and its marginal seas. The abundance of Synechococcus was low in the subarctic ocean and the South China Sea, slightly higher in the western subtropical Pacific and the Tokara Strait, and the highest in the Japan Sea and the East China Sea. Synechococcus with different phycobiliprotein composition co-occurred in the western Pacific Ocean, but their abundance showed apparent geographic differentiation. Two types of CA4 gene island which involved in chromatic acclimation (CA) process were detected in the western Pacific Ocean with geographic segregation; type CA4-A mainly occurred in the subarctic ocean, while type CA4-B dominated in mid-latitude. The distribution of lineages clades I and II in the western Pacific Ocean followed the global distribution pattern that the former dominated in temperate cold waters, while the latter dominated in tropical/subtropical warm waters. Clade IV Synechococcus, which often co-occur with clade I according to previous reports, were rarely found in this study. Clades III, VI, VII, WPC1 and subcluster 5.3 were also the major Synechococcus lineages in the western Pacific Ocean warm waters, but with relatively narrower niche than that of clade II. Our results show that Synechococcus communities with similar phylogenetic composition could contain phenotypes with different pigment composition, and vice versa, suggesting that phylogenetic and pigmentation phenotypic diversity of Synechococcus are raised independently.