N-171. Dominance of Synechococcus clades I and IV during a Coastal Marine Time-Series

V. Tai1, Q. Ren2, I. T. Paulsen3, B. Palenik1;
1Univ. of California, La Jolla, CA, 2J. Craig Venter Inst., Rockville, MD, 3Macquarie Univ., Sydney, AUSTRALIA.

Marine cyanobacteria from the genus Synechococcus are found throughout the world’s oceans and are important contributors to global primary productivity and carbon cycling. Cultured isolates and environmental DNA clone libraries of Synechococcus have demonstrated the diversity of these microbes, however, the natural distribution of this diversity through space and time and the ecological significance of their distribution are still poorly understood. To understand the seasonal dynamics of Synechococcus diversity, we have developed a quantitative PCR strategy using the RNA polymerase C (rpoC) gene and applied it to a three-year time series of surface samples from the Scripps Institution of Oceanography pier (La Jolla, CA). Synechococcus from clades I and IV were dominant throughout the time-series and corresponded with total Synechococcus abundance. A metagenome of flow-cytometry sorted Synechococcus also confirmed the dominance of clades I and IV in this coastal environment. Compared to the genomes of cultured isolates, the metagenome diverged greatly in regions of atypical nucleotide composition suggesting the importance of horizontal gene transfer in the evolution and diversification of these organisms. Of these two dominant clades, Synechococcus from clade IV were typically more abundant, however, those from clade I dominated during periods just prior to the annual spring bloom of Synechococcus. Synechococcus from clades II and III were absent during spring and early summer, but appeared at low abundances in late summer and winter. As the first long term time-series describing Synechococcus population diversity, these seasonal dynamics provide crucial information for understanding the interplay between genetic/genomic diversity, physiology, and the environment.