Chytridiomycota

Abstract

The Chytridiomycota is a group of fungi characterized by the production of zoospores with a single posteriorly directed flagellum. The thalli of these fungi are typically microscopic and varied. The advent of molecular phylogenetics combined with analyses of zoospore ultrastructural characters has transformed our understanding of the relationship of these fungi and has revealed greater genetic diversity than expected. What was once the single order Chytridiales is now ten monophyletic orders. Rozella, Olpidium, and the Blastocladiomycota, organisms once thought to be within the Chytridiomycota, diverge in separate lineages and are no longer included in the Chytridiomycota. The Neocallimasti-gomycota are sister to Chytridiomycota, but they are distinct in their zoospore ultrastructure, behavior of nuclear envelope during mitosis, and specific adapta- tion as anaerobes to digestive systems of herbivores. Molecular characterization of environmental samples demonstrates that zoosporic fungi are widespread and can survive in a range of habitats, from oceans to freshwater and even harsh environments including under artic snow or in exposed soils in alpine regions. The importance of these organisms as parasites, saprotrophs of refractory mate- rials, and components in food webs is discussed. Ways to collect, culture, and characterize these organisms are highlighted. Current classification based on molecular and ultrastructural analyses is described.