Defending the homeland: microbiome molecules provide protection to their vertebrate hosts.

The resident bacterial microbiome may shape and protect the health of vertebrate host. An array of molecules secreted by microbiome may contribute to the ecological stability of the microbiome itself. ELISA, radioactivity, immunofluorescence and cytokines measurements were used to observe the bioactivity and stability of colicin Ia level in oviparous and viviparous animal circulation. Colicin Ia, a protein antimicrobial produced by , is not present in animals at birth, but increases in concentration with the establishment of a stable gut microbiome and drops when the microbiome is experimentally disrupted. Colicin introduced is transported to tissues at concentrations able to prevent or eliminate bacterial infection. Our findings suggest an unexpected benefit provided by the presence of a resident microbiome in the form of active, circulating, bacterially-synthesized antimicrobial molecules.