Parasitic zoosporic eufungi: taxonomic and phylogenetic diversity, ecology, and impacts

Kensuke Seto, Kathryn T. Picard, Gustavo H. Jerônimo, Katelyn M. McKindles, David Rabern Simmons, Jaclyn M. Dee, Maiko Kagami, Carmen L. A. Pires-Zottarelli

Zoosporic eufungi (i.e., chytrids, sensu lato) comprise a phylogenetically and ecologically diverse guild of early diverging fungal phyla (Chytridiomycota, Monoblepharomycota, Neocallimastigomycota, Blastocladiomycota, Sanchytriomycota, Aphelidiomycota, Cryptomycota/Rozellomycota, and Olpidiomycota). While most circumscribed zoosporic eufungi function as decomposers of recalcitrant materials, such as pollen, chitin, and keratin, many taxa are parasites of algae and other microorganisms, land plants, and animals in terrestrial and aquatic ecosystems. The effects of parasitic chytrids on their hosts—and the downstream ecological consequences—are generally poorly understood, particularly when compared to better characterized host-parasite systems in the Dikarya. The most infamous chytrid fungus is the amphibian pathogen Batrachochytrium dendrobatidis, and its discovery and effect on global amphibian populations spurred a renewed interest in the diversity of zoosporic eufungi. Increasingly, research in freshwater and marine habitats has demonstrated that zoosporic eufungi regulate algal communities and serve as an important link between trophic levels in aquatic food webs. As pathogens of land plants, zoosporic eufungi can result in yield losses directly both as a pathogen or by serving as a vector for plant viruses. This chapter explores the diversity of chytrid fungi sensu lato in light of recent reclassifications with an emphasis on species that are parasites and pathogens of a variety of hosts ranging from autotrophs (algae and land plants), unicellular microorganisms (e.g., amoebae, flagellated heterotrophs), and invertebrate and vertebrate animals. The ecosystem dynamics of zoosporic eufungi parasites and pathogens are discussed, highlighting their impact on agriculture and industry.