This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Gut microbiota influence multiple aspects of host physiology, including metabolic and immune functions. Many metabolites produced by gut bacteria can cross the intestinal epithelium (which the bacteria may not be able to cross) and enter host tissues, providing a pathway through which microbial activity can influence host physiology.
However, determining the specific contribution of individual gut bacterial metabolites to host lifespan has remained challenging. To address this gap, a research team led by Associate Professor Shin Kurihara of the Faculty of Biology-Oriented Science and Technology at Kindai University in Japan and Professor Takayuki Kuraishi of Kanazawa University in Japan used gnotobiotic flies colonized with genetically engineered Escherichia coli (E. coli). This experimental system enabled the researchers to compare flies carrying bacteria that could produce polyamines with those carrying bacteria genetically modified to lack polyamine production.
"Polyamines, including putrescine and spermidine, are known gut microbial metabolites associated with improved biological functions and lifespan extension. We wanted to understand whether polyamines produced specifically by gut bacteria can directly influence the lifespan of a host, independent of polyamines obtained from the diet," Kurihara says. The study findings are published online in the journal mBio.
The researchers first examined the effect of dietary polyamines using germ-free flies maintained on a chemically defined, polyamine-free diet supplemented with either putrescine or spermidine. Both supplemented groups had significantly longer lifespans than flies maintained on a diet without polyamines. The mean lifespan was 20.8 days for flies receiving putrescine and 21.1 days for those receiving spermidine, compared with 18.2 days for the polyamine-deficient control group.
The team then investigated whether polyamines produced specifically by gut bacteria could contribute to lifespan extension. The researchers colonized the flies with one of three genetically distinct E. coli strains: SK929, a wild-type strain capable of producing putrescine; SK930, a mutant strain in which three genes involved in putrescine biosynthesis had been deleted; and SK931, a complemented strain capable of producing putrescine. All groups were maintained on a modified polyamine-free diet, allowing the researchers to assess the contribution of bacterial polyamine production.
Putrescine was detected in whole-body homogenates of flies colonized with SK929 and SK931, at approximately 1.2 nmol/mg and 1.3 nmol/mg, respectively. However, it was below the detection limit in flies colonized with SK930. The researchers also detected spermidine in all three groups, consistent with the ability of flies to synthesize polyamines themselves.
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