Intestinal microbiota-derived metabolites have biological importance for the host. Polyamines, such as putrescine and spermidine, are produced by the intestinal microbiota and regulate multiple biological processes. Increased colonic luminal polyamines promote longevity in mice. However, no direct evidence has shown that microbial polyamines are incorporated into host cells to regulate cellular responses. Here, we show that microbial polyamines reinforce colonic epithelial proliferation and regulate macrophage differentiation. Colonisation by wild-type, but not polyamine biosynthesis-deficient, Escherichia coli in germ-free mice raises intracellular polyamine levels in colonocytes, accelerating epithelial renewal. Commensal bacterium-derived putrescine increases the abundance of anti-inflammatory macrophages in the colon. The bacterial polyamines ameliorate symptoms of dextran sulfate sodium-induced colitis in mice. These effects mainly result from enhanced hypusination of eukaryotic initiation translation factor. We conclude that bacterial putrescine functions as a substrate for symbiotic metabolism and is further absorbed and metabolised by the host, thus helping maintain mucosal homoeostasis in the intestine.

Polyamines are aliphatic hydrocarbons with terminal amino groups and are essential for biological activities. It has been reported that polyamines have health-promoting effects in animals, such as the extension of lifespan by polyamine intake. The identification of a high polyamine-producing bacterium from foods could lead to the development of a novel probiotic candidate. We aimed to identify high polyamine-producing bacteria from food, and isolated and collected bacteria from vegetables and fermented foods produced in Japan. We successfully acquired Latilactobacillus curvatus KP 3-4 isolated from Kabura-zushi as a putrescine producing lactic acid bacteria. Comparing the polyamine synthesis capability of L. curvatus KP 3-4 with that of typical probiotic lactic acid bacteria and L. curvatus strains available from the Japan Collection of Microorganisms, it was found that only L. curvatus KP 3-4 was capable of exporting high levels of putrescine into the culture supernatant. The enhancement of putrescine production by the addition of ornithine, and whole-genome analysis of L. curvatus KP 3-4, suggest that putrescine is synthesized via ornithine decarboxylase. The administration of L. curvatus KP 3-4 to germ-free mice increased the concentration of putrescine in the feces.