Fig. 2

The role of fungi in plant break down and metabolism. 1 Schematic diagram of the equine digestive system (red text indicates the foregut, blue text indicates the hindgut). The majority of hindgut digestion occurs in the caecum. 2 Plant matter in the caecum is invaded by penetrative hyphae of anaerobic fungi. 3 Overview of the enzymatic activity of anaerobic fungi (adapted from [62]). Anaerobic fungi degrade plant biomass within the equine caecum through several enzymatic strategies; free carbohydrate active enzymes (CAZymes), cell bound cellulosome complexes and free cellulosomes secreted by the cell. Cell bound cellulosome example given is of glycoside hydrolase 3 which converts cellulose to monosaccharide glucose molecules via β-glucoside activity. These glucose molecules can then be absorbed in the equine gut or enter the fungal metabolic pathway. 4 Example of energy metabolism of Piromyces sp. E2 (adapted from [63]). Glucose molecules enter the glycolysis pathway, the product of which are two pyruvate molecules which either enter a mixed acid fermentation in the cytosol, or the hydrogenosome for ATP generation. Major by-products of fungal energy are indicated by the thick orange arrows. Figure made in BioRender