The human gut bacteria Bacteroides thetaiotaomicron and Fusobacterium varium produce putrescine and spermidine in cecum of pectin-fed gnotobiotic rats

Pectin is a soluble indigestible polysaccharide that stimulates cecal polya mine formation in rats. Bacteroides and fusobacteria, two numerically domin ant bacterial population groups in the large intestine, were found to synth esize in vitro high amounts of spermidine and putrescine. The purpose of th is study was to elucidate the effect of pectin on the polyamine production by defined bacterial species in vivo. Germfree male Wistar rats (n = 18) we re randomly assigned to one of three treatments: (i) monoassociation with B acteroides thetaiotaomicron + fiber-free diet; (ii) diassociation with B. t hetaiotaomicron + Fusobacterium varium + fiber-free diet or (iii) diassocia tion with B. thetaiotaomicron + F. varium + fiber-free diet + 10% pectin. T he cecal contents of monoassociated rats fed fiber-free diet contained larg e amounts (1.51 +/- 0.21 mu mol/dry total cecum content) of spermidine whic h was the major polyamine. The cecum of diassociated rats fed the fiber-fre e diet contained even higher concentrations of spermidine (2.53 +/- 0.21 mu mol/dry total cecum content) and also putrescine, which was now the domina nt polyamine (putrescine 0.32 +/- 0.28 vs. 3.01 +/- 0.28 mu mol/dry total c ecum content; monoassociation vs. diassociation), Pectin consumption by dia ssociated rats led to an additional increase in the cecal concentrations of all polyamines: putrescine, spermidine and spermine were 40, 37 and 100%, respectively, higher in the diassociated rats consuming the pectin diet tha n in those consuming the pectin-free diet. Since the microbial counts in th e cecum did not differ in the diassociated treatment groups, the elevated c oncentrations of polyamines observed in the pectin group must have been due to stimulated bacterial polyamine synthesis, The decline of individual pol yamines from cecum to feces detected at the end of the study in all treatme nt groups and the high microbial counts in the cecum and in feces suggest t hat bacterial polyamines are absorbed in cecum and colon. Pectin stimulates intestinal microbes to synthesize large amounts of polyamines which may be utilized by the host.