Supra-organismal interactions in the human intestine

The term “supraorganism” (which we prefer to the more common but slightly less informative “superorganism”) refers to a collection of individuals which behave as a single unit with enhanced function. It was originally applied to groups of genetically-identical individuals such as social insect colonies (Moritz and Fuchs, 1998), but has since been expanded to include systems comprised of taxonomically-diverse species from all domains of life, as well as viruses (Salvucci, 2012). The human intestine plays host to up to 10¹⁴ bacteria, which outnumber the host's own cells by around an order of magnitude: microbial concentrations in the colon can reach 10¹² cells per gram. There are also large numbers of viruses, predominantly bacteriophages, with at least 10⁹ viral particles present per gram of human feces. Current evidence presents a picture of prevailing homoeostasis between host, microbiome and virome consistent with the description of a supraorganism, which can nevertheless enter a disrupted alternative state termed “dysbiosis.” Here we review this evidence and the potential for the adoption of supra-organismal approaches toward the treatment and prevention of dysbiosis in the future.