Comparison of spatio-temporal dynamics and composition in size-fractionated and unfractionated Northwestern Atlantic microbial communities

Abstract

Size fractionation is a widely applied approach to target specific microbial size ranges, differentiating between larger particle-associated, and smaller free-living microorganisms. To characterize its impact on microbial diversity and its comparability to unfractionated samples, we analyzed 16 weekly ocean samples across five depths during a spring bloom. A universal marker was used to characterize prokaryotes, eukaryotes and chloroplasts comparing single (0.2 {micro}m) or sequential (3 {micro}m and 0.2 {micro}m) filtration. We analyzed unfractionated, fractionated (small and large fractions) and de-fractionated samples. The particle-associated fraction defines the most different community from the other fractions, and combining size fractions (de-fractionating) before or after sequencing produces a community that is most similar to unfractionated samples in terms of composition, and richness dynamics with the exception of very rare taxa. Between 75% and 97% of features are shared, but some discrepancies in relative abundances were unresolved, including for some lineages of free-living Proteobacteria like OM43. The richness trends were consistent, and ANCOM detected at most one significantly different feature between fractionated, and de-fractionated samples, highlighting the similarity in community composition and temporal dynamics between the sets.