title: Comparison of the seasonal variations of Synechococcus assemblage structures in estuarine waters and coastal waters of Hong Kong.
abstract: Seasonal variation in the phylogenetic composition of Synechococcus assemblages in estuarine and coastal waters of Hong Kong was examined through pyrosequencing of the rpoC1 gene. Sixteen samples were collected in 2009 from two stations representing estuarine and ocean-influenced coastal waters, respectively. Synechococcus abundance in coastal waters gradually increased from 3.6 × 10(3) cells ml(-1) in March, reaching a peak value of 5.7 × 10(5) cells ml(-1) in July, and then gradually decreased to 9.3 × 10(3) cells ml(-1) in December. The changes in Synechococcus abundance in estuarine waters followed a pattern similar to that in coastal waters, whereas its composition shifted from being dominated by phycoerythrin-rich (PE-type) strains in winter to phycocyanin-only (PC-type) strains in summer owing to the increase in freshwater discharge from the Pearl River and higher water temperature. The high abundance of PC-type Synechococcus was composed of subcluster 5.2 marine Synechococcus, freshwater Synechococcus (F-PC), and Cyanobium. The Synechococcus assemblage in the coastal waters, on the other hand, was dominated by marine PE-type Synechococcus, with subcluster 5.1 clades II and VI as the major lineages from April to September, when the summer monsoon prevailed. Besides these two clades, clade III cooccurred with clade V at relatively high abundance in summer. During winter, the Synechococcus assemblage compositions at the two sites were similar and were dominated by subcluster 5.1 clades II and IX and an undescribed clade (represented by Synechococcus sp. strain miyav). Clade IX Synechococcus was a relatively ubiquitous PE-type Synechococcus found at both sites, and our study demonstrates that some strains of the clade have the ability to deal with large variation of salinity in subtropical estuarine environments. Our study suggests that changes in seawater temperature and salinity caused by the seasonal variation of monsoonal forcing are two major determinants of the community composition and abundance of Synechococcus assemblages in Hong Kong waters.
authors: Division of Life Science, The Hong Kong University of Science and Technology, Hong Kong.
authors: Xiaomin
authors: X
authors: Xia
authors: Division of Life Science, The Hong Kong University of Science and Technology, Hong Kong.
authors: Nayani K
authors: NK
authors: Vidyarathna
authors: Scripps Institution of Oceanography, University of California, San Diego, San Diego, California, USA.
authors: Brian
authors: B
authors: Palenik
authors: Division of Life Science, The Hong Kong University of Science and Technology, Hong Kong.
authors: Puiyin
authors: P
authors: Lee
authors: Division of Life Science, The Hong Kong University of Science and Technology, Hong Kong liuhb@ust.hk.
authors: Hongbin
authors: H
authors: Liu
mesh_terms: D058491:Bacterial Load; D004269:DNA, Bacterial / Q000235:genetics; D004259:DNA-Directed DNA Polymerase / Q000235:genetics; D063366:Estuaries; D014644:Genetic Variation; D006723:Hong Kong; D008969:Molecular Sequence Data; D010802:Phylogeny; D012621:Seasons; D012623:Seawater / Q000382:microbiology*; D017422:Sequence Analysis, DNA; D046940:Synechococcus / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*
chemical_list: D004269:DNA, Bacterial; D004259:DNA-Directed DNA Polymerase