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Abstract
Tall fescue, Lolium arundinaceum, is the predominant Southeastern US pasture grass, covering 14 million hectares and commonly infected with the endophytic fungus, Epichloë coenophiala. E coenophiala produces bioactive secondary metabolites, some (i.e., ergot alkaloids) are toxic to livestock, leading to fescue toxicosis (FT). The development of FT has been attributed ergot alkaloids but evidence suggests downstream processes may play a role. To investigate this, we employed systems biology approaches across four studies to evaluate differences in the microbiota, metabolome, and multi-compartment microbiota-metabolome interaction (throughout the tall fescue plant and animal) between Angus steers grazing a novel, non-toxic (Max-Q) or toxic (E+) tall fescue across different seasons and/or environmental conditions through 16S (bacteria) and ITS2 (fungi) sequencing, high-resolution metabolomics, and bioinformatics methods. E+ grazing altered the bovine plasma/urine metabolomes (tryptophan/lipid metabolism) and fecal microbiota (increased Ruminococcaceae and Lachnospiraceae) under thermoneutral conditions. Heat stress altered the bovine microbiota/metabolome response to E+, with the E+ microbiota susceptible to harsh environmental conditions. Three bacterial operational taxonomic units (OTUs) associated with plasma/urinary metabolites and pathophysiological endpoints (weight gains) were identified. E. coenophiala altered plant phyllosphere bacterial/fungal microbiota and metabolome, with most E+ effects being plant-specific. While E+ grazing had mixed effects on rumen bacteria, it decreased most ruminal fungi. E+ infection and/or grazing perturbed amino acid and Vitamin B6 metabolism in all biological matrices (plant, rumen liquid, plasma, urine). Targeted network analysis revealed numerous microbial OTUs were significantly associated with E. coenophiala in the plant and rumen, the only matrices where it was detected, with E. coenophiala being more integral to plant network. Integrative interactomics showed similar overall structure to Max-Q and E+ networks, with fecal fungi most important in both networks but aligned taxa being different. Urinary L-metanephrine, L-dopachrome, and pyridoxal were identified as accessible biomarkers of FT dysbiosis in multiple compartments. Multiple Vitamin B family (folate, Vitamin B6, etc.) members were significantly perturbed by E+ and in the E+ integrome networks. Overall, these studies provide an outline of the FT integrome and allow future studies to take a directed approach at the development of molecularly driven management strategies and/or novel FT therapeutics.