Microbial Grazers May Aid in Controlling Infections Caused by the Aquatic Zoosporic Fungus .

Free-living eukaryotic microbes may reduce animal diseases. We evaluated the dynamics by which micrograzers (primarily protozoa) apply top-down control on the chytrid () a devastating, panzootic pathogen of amphibians. Although micrograzers consumed zoospores (∼3 μm), the dispersal stage of chytrids, not all species grew monoxenically on zoospores. However, the ubiquitous ciliate , which likely co-occurs with , grew at near its maximum rate ( = 1.7 d). A functional response (ingestion vs. prey abundance) for , measured using spore-surrogates (microspheres) revealed maximum ingestion ( ) of 1.63 × 10 zoospores d, with a half saturation constant () of 5.75 × 10 zoospores ml. Using these growth and grazing data we developed and assessed a population model that incorporated chytrid-host and micrograzer dynamics. Simulations using our data and realistic parameters obtained from the literature suggested that micrograzers could control and potentially prevent chytridiomycosis (defined as 10 sporangia host). However, simulated inferior micrograzers (0.7 × and 1.5 × ) did not prevent chytridiomycosis, although they ultimately reduced pathogen abundance to below levels resulting in disease. These findings indicate how micrograzer responses can be applied when modeling disease dynamics for and other zoosporic fungi.