DOI: 10.5061/dryad.2rbnzs7s7
title: Data for: Fungal parasitism on diatoms alters formation and bio–physical properties of sinking aggregates: Particle analyses

description: Phytoplankton forms the base of aquatic food webs and element cycling in
 diverse aquatic systems. The fate of phytoplankton-derived organic matter,
 however, often remains unresolved as it is controlled by complex,
 interlinked remineralization and sedimentation processes. We here
 investigate a rarely considered control mechanism on sinking organic
 matter fluxes: fungal parasites infecting phytoplankton. We demonstrate
 that bacterial colonization was promoted 3.5-fold on fungal-infected
 phytoplankton cells in comparison to non-infected cells in a cultured
 model pathosystem (diatom Synedra, fungal microparasite Zygophlyctis, and
 co-growing bacteria), and even ≥17-fold in field-sampled populations
 (Planktothrix, Synedra, and Fragilaria). The Synedra–Zygophlyctis model
 system further revealed that fungal infections reduced the formation of
 aggregates. Moreover, carbon respiration was 2-fold higher and settling
 velocities 11–48% lower for similar-sized fungal-infected
 vs non-infected aggregates. Our data imply that parasites can
 effectively control the fate of phytoplankton-derived organic matter on a
 single-cell to single-aggregate scale, potentially enhancing
 remineralization and reducing sedimentation in freshwater and coastal
 systems.
description: <strong>Formation of sinking aggregates (model system,
 cylinder rotation)</strong> Triplicates of
 non-infected and fungal-infected cultures were grown for six days until
 the infection prevalence had reached 59±3% (<em>N</em>=3
 flasks) in the infected treatment. Thereafter, the cultures were diluted
 with medium to approx. 5,000 cells mL<sup>-1</sup> (resembling
 cell abundances during bloom scenarios) and transferred into rotating
 cylinders (<em>r</em>=8.5 cm, <em>h</em>=10 cm,
 <em>V</em>=2.3 L, bubble-free), to facilitate the aggregation
 of cells due to their stickiness and differential settling behavior (setup
 is shown in Supplementary Fig. S2). The aggregate formation was recorded
 over time using a Mini Deep Focus Plankton Imager (MDPI, Bellamare, La
 Jolla, CA, USA). The MDPI is a ‘shadowgraph imager’ using a near-infrared
 LED light source (A007 Indus star, LED dynamics, Randolph, VT, USA) behind
 a pinhole and a set of identical plano-convex collimator lenses to create
 parallel light beams between the LED light pod and the camera pod
 (Supplementary Fig. S2). Using this parallel light,
 <em>i</em>.<em>e</em>., telecentric optics,
 ensured that all objects (aggregates) were in focus, independent of their
 position between the lenses. We recorded two image sequences per cylinder
 every 2–9 hours. Each sequence lasted for at least one rotation (50
 images). The sampling volume of two image sequences covered 2x 0.35 L,
 equal to 30% of the entire cylinder volume. Automated
 particle analyses in ImageJ provided the number of particles per volume
 and the cross-sectional area <em>A</em> of each particle (used
 to calculate the equivalent circular diameter, denotes as diameter,
 assuming spherical geometry). Aggregates were counted, measured, and
 binned into size classes, in which the upper diameter was 1.3-times the
 lower size class. The resulting eleven size classes ranged from 0.4 to 5.6
 mm (aggregates with <em>ECD</em>&lt;0.4 mm were excluded
 from the data set, and aggregates with <em>ECD</em>&gt;5.6
 mm were not present).
description: Data can be accessed using Image J, Notepad and Excel.