Piromyces struthionis, sp. nov., a new anaerobic gut fungus from the feces of ostriches.

Anaerobic gut fungi (AGF; Neocallimastigomycota) are a clade of basal, zoospore-producing fungi within the subkingdom Chytridiomyceta and known inhabitants of the alimentary tract of animal hosts. To date, 22 genera and 38 species have been described, most originating from herbivorous mammals. Here, we report on the isolation and characterization of a novel species of Neocallimastigomycota from an avian host. Multiple AGF strains were isolated from ostrich feces obtained from a local farm in Oklahoma (USA). All strains formed small, irregular-shaped white colonies with darker centers, displayed a filamentous rhizoidal structure with monocentric thallus developmental patterns, and produced mostly monoflagellated zoospores. The type strain produced terminal sporangia that were predominantly globose, often exhibiting cup-shaped and occasionally elongated sporangiophores. Sporangiophores characteristically exhibited constrictions at irregular intervals, giving them a beads-on-a-string-like appearance. Phylogenetic analysis using the partial nuc 28S rDNA D1-D2 regions (D1-D2 28S), ribosomal internal transcribed spacer 1 (ITS1), and RNA polymerase II large subunit (RPB1) grouped all isolates as a separate species within the genus Piromyces. Transcriptomic analysis indicated an average amino acid identity (AAI) of 80.34% (± 3.27%) between the type species and members of the genus Piromyces and 62.93-76.05% between the type species and all other AGF taxa outside Piromyces. Based on the morphology, phylogenetic analysis, and AAI values, we propose accommodating these strains as a novel species of Piromyces, for which the name Piromyces struthionis is proposed. The type strain for this species is Ost1.