Pecoramyces ruminantium, gen. nov., sp. nov., an anaerobic gut fungus from the feces of cattle and sheep.

The anaerobic gut fungi (AGF) inhabit the rumen and alimentary tracts of multiple ruminant and nonruminant herbivores, belong to a distinct phylum-level lineage (Neocallimastigomycota), and play an important role in plant biomass degradation in many herbivores. As part of a wider effort to obtain AGF with high lignocellulolytic capacities, we isolated and characterized four different AGF strains from the feces of cattle and sheep. Microscopically, isolates produced monocentric thalli and monoflagellated zoospores. Phylogenetic analysis revealed that all isolates formed a monophyletic cluster with strong bootstrap support as a sister clade to the genus Orpinomyces and close to Neocallimastix, an unexpected result because these two genera of AGF form polyflagellated zoospores. Isolates displayed a smooth biofilm-like growth in liquid medium and formed small (0.5-1 mm) pinpoint circular colonies on agar roll tubes. Both endogenous and exogenous sporangia were observed with variable shapes and sizes. Zoospores were mainly spherical, with diameters ranging between 3.8 and 12.5 µm, and mostly a single flagellum. All strains exhibited similar substrate utilization patterns and comparable cellulolytic and xylanolytic activities. Similar ITS1 sequences falling within the same distinctive clade were found on GenBank, with all environmental samples obtained from diverse ruminant and pseudoruminant hosts from three continents, but not from any hindgut-fermenting hosts. Given the high level of sequence divergence between our strains and closest cultured representatives and their distinct microscopic/macroscopic features, we propose a new genus, Pecoramyces, from the name of the taxonomic infraorder Pecora ("horned ruminants" or "higher ruminants"; derived from the Latin word for horned livestock), and a new species, P. ruminantium (since occurrence seems to be specific to ruminant/pseudoruminant foregut, but not hindgut-fermenting mammals).