Diversity of colacosome-interacting mycoparasites expands the understanding of the evolution and ecology of Microbotryomycetes

Mycoparasites in Basidiomycota comprise a diverse group of fungi, both morphologically and phylogenetically. They interact with their hosts through either fusion-interaction or colacosome-interaction. Colacosomes are subcellular structures formed by the mycoparasite at the host-parasite interface, which penetrate the parasite and host cell walls. Previously, these structures were detected in 19 fungal species, usually by means of transmission electron microscopy. Most colacosome-forming species have been assigned to Microbotryomycetes (Pucciniomycotina, Basidiomycota), a highly diverse class, comprising saprobic yeasts, mycoparasites, and phytoparasites. In general, these myco- and phytoparasites are dimorphic organisms, with a parasitic filamentous morph and saprobic yeast morph. We investigated colacosome-forming mycoparasites based on fungarium material, freshly collected specimens, and cultures of yeast morphs. We characterised the micromorphology of filamentous morphs, the physiological characteristics of yeast morphs, and inferred phylogenetic relationships based on DNA sequence data from seven loci. We outline and employ an epifluorescence-based microscopic method to assess the presence and organisation of colacosomes. We describe five new species in the genus Colacogloea, the novel dimorphic mycoparasite Mycogloiocolax gerardii, and provide the first report of a sexual, mycoparasitic morph in Colacogloea philyla and in the genus Slooffia. We detected colacosomes in eight fungal species, which brings the total number of known colacosome-forming fungi to 27. Finally, we revealed three distinct types of colacosome organisation in Microbotryomycetes.