but other examples of important gnotobiotes include Caenorhabditis elegans (C. elegans), Drosophila melanogaster (D. melanogaster), zebrafish, and piglets. Gnotobiotes are used as a controlled environment in which to study host anatomy and physiology, the specific symbiotic interactions between a host and specific microorganisms, and the impacts of chemicals on the host and its microbiota. Mammals Rodents (primarily mice and rats) are the most common mammalian model systems used for studying gnotobiosis and are widely used to study human health relating to the gut and interactions between microorganisms and their host; however, recently there has been a rise in using gnotobiotic mice to study interactions between different microorganisms (microbe-microbe interactions) in the gut. Humanized gnotobiotic mice, or gnotobiotic mice introduced to human intestinal microorganisms by fecal microbiota transplant with human feces, are used in the context of studying gut microbiota and their relationship with host cancers, immune system, and nutrition. Some advantages of gnotobiotic mice and rat systems include the uniformity of the organism, historical prevalence, and established system-specific methods, as well as the ability to obtain reliable gnotobiotic mice and rats commercially. Fish Gnotobiotic fish have been used as a model organism for human health; however, an increased interest in aquaculture for sustainable food production has led to increasing prevalence of gnotobiotic studies focused on maximizing production and maintaining healthy captive populations. The majority of research is still only conducted on a few species of fish, such as the zebra fish. Some of the advantages of gnotobiotic fish systems include high numbers of offspring per reproduction event coupled with fast generation times and eggs that can be sanitized. Plants Gnotobiotic plants are plants that are either grown without microorganisms present (aseptic, axenic, or sterile) or grown in the presence of one (monoxenic) or more than one (polyxenic) known microorganism. To obtain gnotobiotic plants, researchers sterilize seeds using chemical agents (e.g., ethanol, sodium hypochlorite (bleach), hydrogen peroxide) on the surface of the seed. A wide variety of plants have been used to generate gnotobiotic systems such as Arabidopsis thaliana, peanuts, oats, corn, and many others. Similar to animals, gnotobiotic plant systems have been used to study integral components of host physiology (e.g., nitrogen fixation), as well as pathogenic and symbiotic interactions between plants and microorganisms. See also Specific-pathogen-free (SPF) Axenic culture References Ecology terminology Model organisms