Mutualistic gut microbes in humans represent:
Many human gut microorganisms receive a stable, nutrient-rich habitat, while their host gains metabolic and protective functions. Microbial fermentation converts otherwise indigestible substrates into short-chain fatty acids, some taxa synthesize vitamins, and the community can inhibit pathogens through competition and immune modulation. These reciprocal net benefits fit mutualism, although the effect of any particular strain depends on diet, host condition, and location; some residents are merely commensal or can become opportunistic pathogens. Competition would harm both parties through shar
Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 8-13
