Particle size shapes prokaryotic communities and vertical connectivity in the water columns of the slope and central basin of the South China Sea

Sinking of organic matter represents an essential mechanism for sequestration of carbon that is exported from the ocean surface to deeper depths. While recent studies have highlighted the important role of microorganisms in the biological pump, the impact of sinking particles on the vertical connectivity of microbial communities has received limited attention. In this study, we present the microbial profile of sinking particles in the northern slope and the central basin of the marginal South China Sea (SCS) using an in-line size-fractionated water filtration and Illumina high-throughput 16S rRNA amplicon sequencing. We investigate the microbial community composition within organic particles of different size fractions (30, 5, 3, 0.22 μm), and we reveal significant differences in the microbial community structure between these two distinct areas of SCS. The vertical connectivity of microbial communities in the slope and the central basin of SCS shows distinct patterns of microbial dispersal along the water column that occurs via the sinking of organic particles. We find that the microbial communities have different abundances on the different examined particle size fractions and which highlights the role of sinking particles in shaping microbial lifestyles along the water column. Our study underscores the influence of environmental variations on the vertical connectivity of microorganisms and provides additional insights into the marine biological pump under different environmental conditions.