Components of the mammalian gastrointestinal tract (GIT) microbiota. The complex community of the GIT includes bacteria such as major phyla Bacteroidetes, Firmicutes, Actinobacteria, and Proteobacteria; archaea such as family Methanobacteriaceae; and fungi such as genera Candida, Saccharomyces, and Malassezia. Other eukaryotes such as helminths may also variably be present. Additionally, viruses that target these various microbes as well as viruses that directly target humans are critical components of the microbiota. Figure adapted from images created with BioRender.com.