Particles were mainly composed of fucose glycans with only a minor abundance of the other glycans, and particle abundance was directly correlated with the chlorophyll a concentrations. In three provinces, we quantified particle abundance and analysed their glycan composition using four lectins targeting fucose, galactose, N-acetylgalactosamine and mannose. Whereas the <3 µm fraction was primarily composed of SAR11, SAR86, Prochlorococcus and Bacteroidetes of the NS9 and NS5 clades, particle-attached communities were dominated by other Bacteroidetes ( Polaribacter spp.), diverse Gammaproteobacteria including members of the genera Alteromonas and Vibrio, Alphaproteobacteria, Planctomycetes, OM27 and Verrucomicrobia. Using 16S rRNA amplicon sequencing and fluorescence in situ hybridisation, we could show a strong variation between particle-attached and free-living bacterial communities at each station and across the biogeographical provinces – a dynamic likely driven by chlorophyll a concentrations, temperature, and the oxygen content of the respective biogeographical provinces. Samples were taken during an Atlantic Meridional Transect (AMT22), which traversed six distinctive ocean provinces. Using fractionated filtration, we analysed particles of 3 – 10 µm and >10 µm and their microbiomes in thirty-five stations along a latitudinal transect of the Atlantic Ocean and provide new insights into the composition, community dynamics, and catabolic potential of particle-attached bacteria.

Its sinking exports organic carbon from the surface to deep oceans. Particulate organic matter plays a significant role in the marine carbon cycle. 2Sun Yat-sen University, Guangzhou, Guangdong, China.1Department of Molecular Ecology, Max Planck Institute for Marine Microbiology, Bremen, Germany.

Greta Reintjes 1*, Anneke Heins 1, Cheng Wang 1,2 and Rudolf Amann 1

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