Fig. 1.

Cell types in the model pathosystem. (A) Schematic life cycle (asexual) of parasitic chytrids. During phytoplankton blooms, chytrids replicate quickly by asexual reproduction. Free-living, motile zoospores settle onto a phytoplankton cell, encyst, and expand into the host’s interior via rhizoids. New zoospores are produced in each sporangium and eventually discharged into the water to seek out a new host, leaving behind a dead phytoplankton cell. (B–F) Fluorescence microscopy images of the diatom Asterionella, the parasitic chytrid Rhizophydiales, and bacterial cells. B–E show Asterionella and Asterionella-associated cells, and F shows free-living bacteria (turquoise = DAPI-stained bacteria, pink = CF319a-hybridized cells [i.e., Bacteroidetes]). Chitinous cell walls of the chytrid Rhizophydiales in C were stained with WGA (conjugated to Alexa Fluor 488). (White scale bars, 10 µm.) (G) Description of the various cell types. A higher-quality figure is available on Figshare (https://doi.org/10.6084/m9.figshare.14614155).