The anaerobic gut fungal community in ostriches ( Struthio camelus )

Anaerobic gut fungi (AGF; Neocallimastigomycota ) are essential for plant biomass degradation in herbivores. While extensively studied in mammals, information regarding their occurrence, diversity, and community structure in non-mammalian hosts remains sparse. Here, we report on the AGF community in ostriches ( Struthio camelus ), herbivorous, flightless, hindgut fermenting members of the class Aves (birds). Culture-independent diversity surveys of fecal samples targeting the D2 region of the large ribosomal subunit (28S rRNA) revealed a uniform community with low alpha diversity. The community was mostly comprised of sequences potentially representing two novel species in the genus Piromyces, and a novel genus in the Neocallimastigomycota . Sequences affiliated with these novel taxa were absent or extremely rare in datasets derived from mammalian and tortoise samples, indicating a strong pattern of AGF-host association. One Piromyces strain (strain Ost1) was successfully isolated. Transcriptomics-enabled molecular dating analysis suggested a divergence time of ≈ 30 Mya, a time frame in line with current estimates for ostrich evolution. Comparative gene content analysis between strain Ost1 and other Piromyces species from mammalian sources revealed a high degree of similarity. Our findings expand the range of AGF animal hosts to include members of the birds (class Aves ), highlight a unique AGF community adapted to the ostrich alimentary tract, and demonstrate that – like mammals – coevolutionary phylosymbiosis (i.e. concurrent evolution of AGF and their animal hosts) plays a central role in explaining current AGF distribution patterns in Aves .