Heather E. Hallen-Adams

　　Department of Food Science and Technology, University of Nebraska-Lincoln, USA

　　We are in the Age of the Microbiome, with new studies appearing constantly and whole journals devoted to the role of the human microbiome in sickness and in health. Many species of fungi have been detected in the healthy human gut, where they are the most significant eukaryotic members of the microbiome; however, nearly half of all taxa reported have only been fund in one study or one sample. Fungi capable of growing in and colonizing the gut are limited to a small number of species, mostly Candida yeasts and yeasts in the family Dipodascaceae. Malassezia and the filamentous fungus Cladosporium are potential colonizers; more work is needed to clarify their role. Other commonly-detected fungi come from the diet or environment but either do not or cannot colonize (Penicillium and Debaryomyces species, which are common on fermented foods but cannot grow at human body temperatures), while still others have dietary sources (Saccharomyces cerevisiae, fermentation agent and sometime probiotic) yet may grow and influence gut ecology. Diet strongly influences gut fungal composition, with vegetarians having notably different composition than meat eaters. Gut fungal composition appears less stable than bacterial composition, and is highly susceptible to environmental factors.