Blastocladiomycota

Abstract

The Blastocladiomycota are posteriorly uniflagellated zoosporic fungi found as saprotrophs and parasites primarily in freshwater and soil. Once considered Chytridiomycota, phylogenetically they are a monophyletic group divergent from other zoosporic fungi, clustering among the nonzoosporic fungi. Their thalli range from monocentric, polycentric, tubular, to hyphal and are unusual among fungi in exhibiting alternation of a haploid gametophytic generation with a diploid sporophytic generation. Thick-walled resistant sporangia are the sites of meiosis and aid in the survival of the organism when environmental conditions become adverse. The hallmark of the group is the ultrastructural architecture of their zoospores, which includes a single nucleus proximal to the kinetosome, an aggregated cluster of ribosomes capping the nucleus anteriorly, and a lateral microbody-lipid globule complex (MLC). In addition to being the center for utilization of stored energy, the MLC has been implicated in rhodopsin-based photoreception and signal transduction in response to blue-green light. Inverte- brates, plants, algae, oomycetes, and other blastoclads serve as hosts of parasitic members. For example, Paraphysoderma is a highly destructive pathogen of algae grown in mass cultures for biofuels and pharmaceuticals. As a pathogen of mosquitoes, Coelomomyces has been explored as a biocontrol agent, but its life cycle requirement for alternation of hosts makes this a difficult system to main- tain. The saprotrophs Allomyces and Blastocladiella are emerging as model organisms in developmental biology, genetics, physiology, and genomics.