Biosynthesis of bromoform by Curvularia fungi provides a natural pathway to mitigate enteric methane emissions from ruminants

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• Methane emissions from ruminant livestock are a major greenhouse gas source. • Bromoform feed additives can reduce livestock methane by >90 %. • Curvularia soil fungi produce bromoform and prevent rumen methane emission. • These natural, culturable fungi offer a unique climate change strategy. The ruminant livestock industry is the largest agricultural emissions source of anthropogenic greenhouse gases, primarily from enteric methane. Several technologies, both natural and synthetic are being investigated to mitigate enteric methane emissions. Macroalgae derived feed ingredients that contain bromoform, a recognised inhibitor of methanogenesis, are an effective natural approach for methane mitigation. However, producing sufficient biomass economically to satisfy the livestock industry at a global scale is challenging. Here we demonstrate that a Curvularia soil fungi isolate can be cultured to produce bromoform and subsequently inhibit methanogenesis in pure cultures of Methanobrevibacter smithii and in mixed cultures of ovine rumen fluid. This highly culturable fungal species produces no known toxins and creates an exciting new, scalable and natural alternative for reducing ruminant livestock emissions.