Peribolosporomycetes class. nov.: description of a new heat resistant and osmotolerant basidiomycete lineage, represented by Peribolospora gen. nov., P. kevripleyi sp. nov., and P. baueri sp. nov.

Heat resistance is the ability to survive short, extreme temperature stresses, exceeding the own growth temperature by far. Despite their occurrence in natural substrates and their relevance for the food and healthcare industry, the diversity of fungi with heat resistance abilities is poorly studied. Sampling of boreal forest soils in Canada in combination with a heat-shock treatment (75 °C, 30 min) yielded, among others, four heat resistant, mesophilic fungal isolates. Based on rDNA barcode sequences, the novel isolates were assigned to Basidiomycota. In this study, we use macromorphological and micromorphological observations, cultivation assays and comparative genomics for physiological characterization, interspecific differentiation, and phylogenetic placement of these isolates. A phylogeny of 38 single-copy orthologous genes, an orthology analysis, and septal pore type analysis revealed the isolates as representatives of two new basidiomycetous species of the novel class Peribolosporomycetes, a sister lineage to all other members of Ustilaginomycotina. Further genomic and phenotypic data support two different species (Peribolospora kevripleyi, Peribolospora baueri), which are heat resistant and osmotolerant.