Effects of endophytic and saprophytic fungi on in vitro methanogenesis

The predominance of pasture in the diet of ruminants in New Zealand presents specific challenges for mitigation of enteric methane emissions. However, there is preliminary evidence from both laboratory and animal-based studies that some fungi may suppress enteric methanogenesis. This study determined the antimethanogenic potential of a range of endophytic (Neotyphodium species) and saprophytic (Geotrichum, Monascus, Mortierella and Penicillium species) fungi. Candidate fungi were selected on the basis of their production of various classes of secondary compounds and screened in an in vitro batch-culture fermentation assay. No strains of endophyte in ryegrass or tall fescue suppressed methanogenesis compared with their endophyte-free controls. The supernatant fractions from three strains of Mortierella wolfii were the most promising fungi identified. They suppressed methanogenesis as effectively as an inhibitor of methanogenesis (bromoethane sulphonate at 30 mu moles/L), without also reducing overall fermentation. These strains should be investigated further by screening fresh cultures grown under contrasting conditions to establish some variation in putative bioactive compounds.