# Seasonal Variations of Community Structure and Functional Genes of Synechococcus in the Subtropical Coastal Waters: Insights from FACS and High-Throughput Sequencing

## TL;DR

This study explores how Synechococcus communities and their genes change seasonally in Xiamen's coastal waters using advanced sorting and sequencing techniques.

## Contribution

The study reveals previously undetected Synechococcus strains and their seasonal functional dynamics in subtropical coastal waters.

## Key findings

- FACS revealed low-abundance Synechococcus strains missed by in situ sampling.
- 24 clades of Synechococcus subclusters were detected, indicating high diversity.
- Summer Synechococcus populations showed enhanced metabolic activity compared to winter.

## Abstract

Synechococcus plays a pivotal role in the marine biogeochemical cycle. Advances in isolation techniques and high-throughput sequencing have expanded our understanding of the diversity of the Synechococcus community. However, their genomic diversity, functional dynamics and seasonal variations in the coastal waters are still not well known. Here, seawater samples were collected seasonally (March, June, August, December) from three stations in the coastal waters of Xiamen. Using fluorescence-activated cell sorting (FACS), we isolated 1000 Synechococcus cells per sample and performed ITS amplicon sequencing and metagenomic sequencing to analyze the seasonal variations in community structure and functional genes of Synechococcus. Firstly, we conducted a comparative analysis of in situ data and FACS data from three sampling sites in August. FACS samples revealed low-abundance Synechococcus strains underdetected by in situ samples. In addition, 24 clades representing Synechococcus subclusters S5.1, S5.2, and S5.3 were detected from three in situ samples and twelve FACS samples, suggesting the high diversity of Synechococcus in the coastal waters of Xiamen. Furthermore, the Synechococcus community displayed pronounced seasonal variations, and temperature significantly influenced the variations in Synechococcus community composition. Additionally, Synechococcus populations exhibit seasonal functional dynamics, with enhanced metabolic activity in summer characterized by higher numbers of functional genes associated with metabolic pathways compared to winter samples. Altogether, this study underscored the significance of FACS and high-throughput sequencing to reveal the diversity and functional dynamics of Synechococcus.