Data for: Fungal parasitism on diatoms alters formation and bio–physical properties of sinking aggregates: Particle analyses

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 aggregat..., Formation of sinking aggregates (model system, cylinder rotation)
Triplicates of non-infected and fungal-infected cultures were grown for six days until the infection prevalence had reached 59±3% (N=3 flasks) in the infected treatment. Thereafter, the cultures were diluted with medium to approx. 5,000 cells mL-1 (resembling cell abundances during bloom scenarios) and transferred into rotating cylinders (r=8.5 cm, h=10 cm, V=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..., Data can be accessed using Image J, Notepad and Excel.