Fig. 2. Microbial succession during the growth and demise of algal blooms with different viral loads.

a Nanoeukaryotic (black) and bacterial (red) microbial succession throughout the experiment duration, averaged across enclosures. Each row is a taxon with bacteria (ASVs) in red and eukaryotes (named genera) in black. The trophic modes of each ASV are detailed in the box color with autotrophs in green, heterotrophs in gray, and mixotrophs in green/gray. Days are shown in columns. 18S species are grouped by clusters of different colors and taxa of special interest (d, g) are indicated on the right of the heatmap. 16S abbreviations denote taxonomy at the order level: F: Flavobacteriales, R: Rhodobacterales, A: Alteromonadales, C: Cytophagales, CV: Cellvibrionales, MC: Micrococcales, P: Pseudomonadales, PC: Puniceicoccales, SM: Sphingomonadales, SP: Saprospirales. b Succession of 18S-based ASVs in the 2–20 μm fraction, clustered by similarity of their relative abundance dynamics averaged across bags. The shaded area represents the standard deviation within each cluster, centered around the mean normalized abundance of species in that cluster. The absolute abundance of E. huxleyi enumerated with flow cytometry is overlaid as a guide (black line, not to scale). Each cluster is normalized to its own maximum abundance and their species composition is detailed in (a, c). Relative abundance of major bacterial orders throughout the bloom, averaged for all enclosures using 16S amplicon sequencing of the 0.2–2 μm fraction. The absolute abundance of E. huxleyi enumerated with flow cytometry is overlaid as a guide (black line, not to scale). Shaded areas represent standard deviations across bags. d Relative abundance of different Flavobacteriales and Rhodobacterales genera within each order averaged across all enclosures. The dark line on the top represents E. huxleyi abundance trends as a guide. The letters F1-F10 and R1-R7 refer to (a). e Relative abundance of bacteria in the free-living versus particle-attached size fractions. Asterisks indicate fold-differences between size fractions (*: >2.5; **: >10). f Rate at which bacteria and nanoeukaryotic community similarities change over time. Nanoeukaryotic communities initially turnover much faster than the bacterial ones (for each time point until day 8, p < 0.01 by two-sided Mann–Whitney test with Bonferroni multiple testing correction). Lines and shaded areas represent mean and standard deviation across bags, respectively. g Selection of eukaryotic and bacterial ASVs that are overrepresented or underrepresented in bag 7. The letters P1, P2, P3 and S, F1, F10 refer to (a). h Correlation, per bag and per 16S or 18S ASV, between total viral load and percentage dissimilarity in microbial composition from one day to another. The divergence of a bag is defined as the change in pairwise Bray–Curtis distance between the focal bag and all other bags from the start of the E. huxleyi bloom to its demise. Source data are provided as a Source Data file.