| description |
The Southern Ocean covers a large area of planet and it’s characterized by a high phytoplankton biomass production. Particulate carbon is exported from the photic zone to the deep ocean and remineralized while sinking by bacterioplankton communities. Little is known about the relationship between free-living and particle associated bacterioplankton communities as well as between coastal and pelagic ones. In the present study we report the analysis of bacterioplankton communities from the Southern Ocean of three size fractions of the bacterioplankton (>8 µm, 8-3 µm, 3-0.22 µm). Samples were collected in the mesopelagic and bathypelagic zone of coastal and pelagic regions, and Illumina sequencing of the V5-V6 region of the 16S rRNA was performed to assess diversity and community composition. Particle associated communities had a higher OTU richness and evenness than free-living ones. Taxonomic analysis revealed that the three size fraction of the plankton exhibited a shift in their community composition from the free-living fraction toward the particles one. A large number of OTUs belonging to diverse phyla (Bactereoidetes, Planctomycetes, Betaproteobacteria, Deltaproteobacteria and Verrucomicriobia) were significantly enriched on particles, while very few were preferentially found in the free-living community. The data showed that lifestyle (free-living vs particle associated) and sampling location (pelagic vs costal) strongly influenced bacatreioplankton communities. Surprisingly we found that depth explained only marginal part of the total variation (~12%), suggesting that selective processes driven by depth have a smaller effect in the Southern Ocean when compared to lifestyle (25%) and sampling location (31%). Overall these data might indicate a stronger influence of phytoplankton and particle export on bacterioplankton communities from the Southern Ocean compared to other regions of the planet. |