Immune-directed support of rich microbial communities in the gut has ancient roots

Abstract

The animal gut serves as a primary location for the complex host-microbe interplay that is essential for homeostasis and may also reflect the types of ancient selective pressures that spawned the emergence of immunity in metazoans. In this review, we present a phylogenetic survey of gut host-microbe interactions and suggest that host defense systems arose not only to protect tissue directly from pathogenic attack but also to actively support growth of specific communities of mutualists. This functional dichotomy resulted in the evolution of immune systems much more tuned for harmonious existence with microbes than previously thought, existing as dynamic but primarily cooperative entities in the present day. We further present the protochordate Ciona intestinalis as a promising model for studying gut host-bacterial dialogue. The taxonomic position, gut physiology and experimental tractability of Ciona offer unique advantages in dissecting host-microbe interplay and can complement studies in other model systems.

Unravelling methanogenesis in ruminants, horses and kangaroos: the links between gut anatomy, microbial biofilms and host immunity

“…The microbiota present include viruses, Archaea, bacteria, protozoa and fungi that have evolved in communities that exhibit intimate between-species and species-host tissue associations. Considerable advances have been made in our understanding of the ecology of the gut microbiota of mammals and mutualistic interactions among the microbiota with the host's immune systems have been recognised and explored (for recent reviews, see Eberl 2010;Bevins and Salzman 2011;Sansonetti 2011;Schluter and Foster 2012;Bang et al 2014;Dishaw et al 2014). These associations control many aspects of the physiology and biochemistry of the host, to such an extent that they are often regarded as an integral component of what has been dubbed the 'super organisms' (Eberl 2010).…”

Earthworms and Cadmium - heavy metal resistant gut bacteria as indicators for heavy metal pollution in soils?

“…Additionally, the earthworm gut has the ability to discriminate between beneficial and harmful bacteria. For instance, some bacteria show tolerance to the antimicrobial activity of digestive fluids derived from the earthworm gut (19, 20). The maintained earthworm gut harbours a microbial community that is involved in food metabolism, thereby establishing bioavailable vitamins and nutrients, and pathogen protection (20–22).…”

“…For instance, some bacteria show tolerance to the antimicrobial activity of digestive fluids derived from the earthworm gut (19, 20). The maintained earthworm gut harbours a microbial community that is involved in food metabolism, thereby establishing bioavailable vitamins and nutrients, and pathogen protection (20–22). Bacteria involved in these processes fall into one of the four physiological groups: plant growth promoters, free-living nitrogen fixers, biocides and phosphate solubilizers (13).…”

Markedly Elevated Antibody Responses in Wild versus Captive Spotted Hyenas Show that Environmental and Ecological Factors Are Important Modulators of Immunity

“…Natural antibodies (nAbs) are germline encoded, undergo little or no somatic hypermutation, and are thus largely non-specific, but can be rapidly induced by the microbiota or infection by pathogens [29][30][31][32]. By contrast, specific antibodies produced by B-2 cells, are primarily of the IgG isotype in non-mucosal regions, are produced in response to a strong stimulus, such as an infection, and undergo somatic mutation and affinity maturation [31].…”