International Symposium on Ruminant Physiology: Rumen fungi, archaea, and their interactions

Anaerobic gut fungi (AGF) were the last phylum to be identified within the rumen microbiome and account for 7% to 9% of microbial biomass. They produce potent lignocellulases that degrade recalcitrant plant cell walls, and rhizoids that can penetrate the cuticle of plant cells, exposing internal components to other microbiota. Interspecies H₂ transfer between AGF and rumen methanogenic archaea is an essential metabolic process in the rumen that occurs during the reduction of CO₂ to CH₄ by methanogens. This symbiotic relationship is bolstered by hydrogensomes, fungal organelles that generate H₂ and formate. Interspecies H₂ transfer prevents the accumulation of reducing equivalents that would otherwise impede fermentation. The extent to which hydrogenosomes serve as a conduit for H₂ flow to methanogens is unknown, but it is likely greater with low-quality forages. Strategies that alter the production of CH₄ could also have implications for H₂ transfer by anaerobic fungi. Understanding the factors that drive these interactions and H₂ flow could provide insight into the effect of reducing CH₄ production on the activity of ruminal fungi and the digestion of low-quality feeds.