Anaerobic fungi (AF) play an essential role in feed conversion due to their potent fiber degrading enzymes and invasive growth. Much has been learned about this unusual fungal phylum since the paradigm shifting work of Colin Orpin in the 1970s, when he characterized the first AF. Molecular approaches targeting specific phylogenetic marker genes have facilitated taxonomic classification of AF, which had been previously been complicated by the complex life cycles and associated morphologies. Although we now have a much better understanding of their diversity, it is believed that there are still numerous genera of AF that remain to be described in gut ecosystems. Recent marker-gene based studies have shown that fungal diversity in the herbivore gut is much like the bacterial population, driven by host phylogeny, host genetics and diet. Since AF are major contributors to the degradation of plant material ingested by the host animal, it is understandable that there has been great interest in exploring the enzymatic repertoire of these microorganisms in order to establish a better understanding of how AF, and their enzymes, can be used to improve host health and performance, while simultaneously reducing the ecological footprint of the livestock industry. A detailed understanding of AF and their interaction with other gut microbes as well as the host animal is essential, especially when production of affordable high-quality protein and other animal-based products needs to meet the demands of an increasing human population. Such a mechanistic understanding, leading to more sustainable livestock practices, will be possible with recently developed -omics technologies that have already provided first insights into the different contributions of the fungal and bacterial population in the rumen during plant cell wall hydrolysis.

Anaerobic Microbiology Lab ICAR National Dairy Research Institute Dairy Microbiology Division ICAR National Dairy Research Institute Karnal India

Department of Chemistry Bioscience and Environmental Engineering University of Stavanger Stavanger Norway

Gut Microbiome Lab ICAR Directorate of Poultry Research Indian Council of Agricultural Research Hyderabad India

Laboratory of Anaerobic Microbiology Institute of Animal Physiology and Genetics Czech Academy of Sciences Prague Czechia

Laboratory of Microbiology Wageningen University and Research Wageningen Netherlands

Systems Microbiology and Natural Product Discovery Laboratory Department of Animal Science University of California Davis Davis CA United States

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Patterns and determinants of the global herbivorous mycobiome

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