Gut bacteria use weapons to hold their ground

In the guts of wild mice, a bacterium called Bacteroides acidifaciens carries a weapon: the type VI secretion system (T6SS), a protein complex that bacteria use to inject toxic molecules directly into neighboring cells. The researchers, publishing in eLife, show that this system does not only work in laboratory strains, but also within a complex, naturally evolved gut microbiome. Bacteria that lost the T6SS gradually disappeared from the gut over time, even if they could initially survive there.

The gut microbiome is a community of hundreds of bacterial species. Which strains survive and which disappear depends on diet, the immune system, and the competition between bacteria themselves. Until now, the type VI secretion system had been studied mainly under laboratory conditions. This study is among the first to demonstrate that the system also shapes the composition of gut bacteria in a living animal.

A transferable weapon

Notably, the gene encoding the T6SS is located on a mobile genetic element: a piece of DNA that can jump from one bacterium to another. The researchers found evidence that this weapon was recently exchanged between different bacterial species in the gut. That makes gut dynamics more complex than previously thought: bacteria share not only nutrients and space, but also weapons.

Connection to health and aging

This is relevant to longevity research because the composition of the gut microbiome changes with age. Certain strains increase, others disappear. If bacterial weaponry partly determines which strains persist, then the aging gut microbiome is partly shaped by this microbial competition. How that affects health remains an open question. The findings do offer a new mechanism for better understanding microbiome shifts in aging.

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