TY - JOUR T1 - Proteome specialization of anaerobic fungi during ruminal degradation of recalcitrant plant fiber JF - bioRxiv DO - 10.1101/2020.01.16.907998 SP - 2020.01.16.907998 AU - Live H. Hagen AU - Charles G. Brooke AU - Claire Shaw AU - Angela D. Norbeck AU - Hailan Piao AU - Magnus Ø. Arntzen AU - Heather Brewer AU - Alex Copeland AU - Nancy Isern AU - Anil Shukla AU - Simon Roux AU - Vincent Lombard AU - Bernard Henrissat AU - Michelle A. O’Malley AU - Igor V. Grigoriev AU - Susannah Tringe AU - Roderick Mackie AU - Ljiljana Pasa-Tolic AU - Phillip B. Pope AU - Matthias Hess Y1 - 2020/01/01 UR - http://biorxiv.org/content/early/2020/01/19/2020.01.16.907998.abstract N2 - The rumen harbors a complex microbial mixture of archaea, bacteria, protozoa and fungi that efficiently breakdown plant biomass and its complex dietary carbohydrates into soluble sugars that can be fermented and subsequently converted into metabolites and nutrients utilized by the host animal. While rumen bacterial populations have been well documented, only a fraction of the rumen eukarya are taxonomically and functionally characterized, despite the recognition that they contribute to the cellulolytic phenotype of the rumen microbiota. To investigate how anaerobic fungi actively engage in digestion of recalcitrant fiber that is resistant to degradation, we resolved genome-centric metaproteome and metatranscriptome datasets generated from switchgrass samples incubated for 48 hours in nylon bags within the rumen of cannulated dairy cows. Across a gene catalogue covering anaerobic rumen bacteria, fungi and viruses, a significant portion of the detected proteins originated from fungal populations. Intriguingly, the carbohydrate-active enzyme (CAZyme) profile suggested a domain-specific functional specialization, with bacterial populations primarily engaged in the degradation of polysaccharides such as hemicellulose, whereas fungi were inferred to target recalcitrant cellulose structures via the detection of a number of endo- and exo-acting enzymes belonging to the glycoside hydrolase (GH) family 5, 6, 8 and 48. Notably, members of the GH48 family were amongst the highest abundant CAZymes and detected representatives from this family also included dockerin domains that are associated with fungal cellulosomes. A eukaryote-selected metatranscriptome further reinforced the contribution of uncultured fungi in the ruminal degradation of recalcitrant fibers. These findings elucidate the intricate networks of in situ recalcitrant fiber deconstruction, and importantly, suggests that the anaerobic rumen fungi contribute a specific set of CAZymes that complement the enzyme repertoire provided by the specialized plant cell wall degrading rumen bacteria. ER -