Scientists discovered the elixir of youth in the gut

Bacteria living in the gut produce substances capable of directly extending the lifespan of their host. This is the conclusion reached by Japanese scientists from Kindai University and Kanazawa University, who published the results of their work in the prestigious scientific journal mBio.

The gut microbiota has long been known for its influence on numerous processes in the body — from metabolism to immune system function. Metabolites produced by gut bacteria can cross the intestinal epithelial barrier and penetrate host tissues. However, until now, scientists had been unable to precisely determine what contribution individual bacterial metabolites make to lifespan.

To solve this puzzle, the researchers turned to an elegant experimental model — gnotobiotic fruit flies (Drosophila) colonized with genetically modified strains of Escherichia coli (E. coli). This approach allowed them to directly compare insects whose bacteria could produce polyamines with those whose bacteria had the corresponding genes deliberately deleted.

"Polyamines, including putrescine and spermidine, are well-known metabolites of gut microbes that have been associated with improved biological functions and lifespan extension. Our goal was to determine whether polyamines produced specifically by gut bacteria could directly influence the host's lifespan — independently of polyamines obtained from food," explained Dr. Shin Kurihara, who led the study.

In the first stage, the scientists tested the effect of dietary polyamines on germ-free flies maintained on a chemically defined diet — without polyamines, with the addition of putrescine, or with the addition of spermidine. The result was impressive: both supplemented groups lived significantly longer than control individuals. The average lifespan was 20.8 days for those receiving putrescine and 21.1 days for those receiving spermidine — compared to only 18.2 days in the control group.

In the next stage, the team moved on to the key question: can polyamines produced specifically by gut bacteria contribute to lifespan extension? To address this, flies were colonized with one of three genetically distinct E. coli strains: SK929 (wild type, producing putrescine), SK930 (a mutant with three putrescine biosynthesis genes deleted), and SK931 (a complemented strain with restored ability to produce putrescine). All groups were maintained on a modified diet completely devoid of polyamines.

Putrescine was detected in whole-fly homogenates of flies colonized with strains SK929 and SK931, at levels of approximately 1.2 and 1.3 nmol/mg respectively. In flies with strain SK930, its content was below the detection limit. Spermidine, meanwhile, was detected in all three groups, which is consistent with the flies' own ability to synthesize polyamines. Elevated levels of putres