AUTHOR=Farthing Hazel N. , Jiang Jiamei , Henwood Alexandra J. , Fenton Andy , Garner Trent W. J. , Daversa David R. , Fisher Matthew C. , Montagnes David J. S. 

TITLE=Microbial Grazers May Aid in Controlling Infections Caused by the Aquatic Zoosporic Fungus Batrachochytrium dendrobatidis

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.592286

DOI=10.3389/fmicb.2020.592286

ISSN=1664-302X

ABSTRACT=<p>Free-living eukaryotic microbes may reduce animal diseases. We evaluated the dynamics by which micrograzers (primarily protozoa) apply top-down control on the chytrid <italic>Batrachochytrium dendrobatidis</italic> (<italic>Bd</italic>) 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 <italic>Tetrahymena pyriformis</italic>, which likely co-occurs with <italic>Bd</italic>, grew at near its maximum rate (<italic>r</italic> = 1.7 d<sup>–1</sup>). A functional response (ingestion vs. prey abundance) for <italic>T. pyriformis</italic>, measured using spore-surrogates (microspheres) revealed maximum ingestion (<italic>I</italic><sub><italic>max</italic></sub>) of 1.63 × 10<sup>3</sup> zoospores d<sup>–1</sup>, with a half saturation constant (<italic>k</italic>) of 5.75 × 10<sup>3</sup> zoospores ml<sup>–1</sup>. 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 <italic>Bd</italic> and potentially prevent chytridiomycosis (defined as 10<sup>4</sup> sporangia host<sup>–1</sup>). However, simulated inferior micrograzers (0.7 × <italic>I</italic><sub><italic>max</italic></sub> and 1.5 × <italic>k</italic>) 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 <italic>Bd</italic> and other zoosporic fungi.</p>