Dataset Information

Synechococcus Assemblages across the Salinity Gradient in a Salt Wedge Estuary.

ABSTRACT: Synechococcus are the most abundant and widely distributed picocyanobacteria in the ocean. The salt-wedge type of estuary possesses the complete horizontal and vertical gradient of salinity together with other physical and chemical parameters. In order to reveal whether such a complex environmental gradient harbors a high diversity of Synechococcus, we investigated the abundance, taxonomic composition and pigment genetic diversity of Synechococcus in surface and bottom waters across the salinity gradient in a salt-wedge estuary by flow cytometric analysis and pyrosequencing of the rpoC1 gene and cpcBA operon (encoding phycocyanin). Synechococcus were ubiquitously distributed in the studied region, with clear spatial variations both horizontally and vertically. The abundance and diversity of Synechococcus were low in the freshwater-dominated low salinity waters. By pyrosequencing of the rpoC1 gene, we have shown that with the increase of salinity, the dominant Synechococcus shifted from the freshwater Synechococcus to the combination of phylogenetic subcluster 5.2 and freshwater Synechococcus, and then the strictly marine subcluster 5.1 clade III. Besides, the composition of Synechococcus assemblage in the deep layer was markedly different from the surface in the stratified waters (dissimilarities: 40.32%-95.97%, SIMPER analysis). High abundance of clade III Synechococcus found in the brackish waters may revise our previous understanding that strains of this clade prefers oligotrophic environment. Our data also suggested that both the phylogenetic subcluster 5.3 Synechococcus, a lineage that was not well understood, and subcluster 5.1 clade I, a typical cold water lineage, were widely distributed in the bottom layer of the estuary. Clade I detected in the studied region was mainly contributed by subclade IG. Analysis of the cpcBA operon sequences revealed niche partitioning between type 1 and type 3 Synechococcus, with type 2 distributed broadly across the whole environmental gradients. Our results suggest that the salt wedge estuary provides various niches for different lineages of Synechococcus, making it an environment with high Synechococcus diversity compared with adjacent freshwater and shelf sea environments.

SUBMITTER: Xia X

PROVIDER: S-EPMC5498518 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature

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Synechococcus Assemblages across the Salinity Gradient in a Salt Wedge Estuary.

Xia Xiaomin X Guo Wang W Tan Shangjin S Liu Hongbin H

Frontiers in microbiology 20170706

Synechococcus are the most abundant and widely distributed picocyanobacteria in the ocean. The salt-wedge type of estuary possesses the complete horizontal and vertical gradient of salinity together with other physical and chemical parameters. In order to reveal whether such a complex environmental gradient harbors a high diversity of Synechococcus, we investigated the abundance, taxonomic composition and pigment genetic diversity of Synechococcus in surface and bottom water ...[more]

PMID: 28729864

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Project description:Sabkhas are hypersaline, mineral-rich, supratidal mudflats that harbor microbes that are adapted to high salt concentration. Sabkha microbial diversity is generally studied for their community composition, but less is known about their genetic structure and heterogeneity. In this study, we analyzed a coastal sabkha for its microbial composition using 16S rDNA and whole metagenome, as well as for its population genetic structure. Our 16S rDNA analysis show high alpha diversity in both inner and edge sabkha than outer sabkha. Beta diversity result showed similar kind of microbial composition between inner and edge sabkha, while outer sabkha samples show different microbial composition. At phylum level, Bacteroidetes (~ 22 to 34%), Euryarchaeota (~ 18 to ~ 30%), unclassified bacteria (~ 24 to ~ 35%), Actinobacteria (~ 0.01 to ~ 11%) and Cyanobacteria (less than 1%) are predominantly found in both inside and edge sabkha regions, whereas Proteobacteria (~ 92 to ~ 97%) and Parcubacteria (~ 1 to ~ 2%) are predominately found in outer sabkha. Our 225 metagenomes assembly from this study showed similar bacterial community profile as observed in 16S rDNA-based analysis. From the assembled genomes, we found important genes that are involved in biogeochemical cycles and secondary metabolite biosynthesis. We observed a dynamic, thriving ecosystem that engages in metabolic activity that shapes biogeochemical structure via carbon fixation, nitrogen, and sulfur cycling. Our results show varying degrees of horizontal gene transfers (HGT) and homologous recombination, which correlates with the observed high diversity for these populations. Moreover, our pairwise population differentiation (Fst) for the abundance of species across the salinity gradient of sabkhas identified genes with strong allelic differentiation, lower diversity and elevated nonsynonymous to synonymous ratio of variants, which suggest selective sweeps for those gene variants. We conclude that the process of HGT, combined with recombination and gene specific selection, constitute the driver of genetic variation in bacterial population along a salinity gradient in the unique sabkha ecosystem.

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Synechococcus Assemblages across the Salinity Gradient in a Salt Wedge Estuary.

Publications

<i>Synechococcus</i> Assemblages across the Salinity Gradient in a Salt Wedge Estuary.

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