In recent years, scientists have begun to reveal the myriad ways that gut microbes can impact our health; they have identified relationships between bacteria in the gastrointestinal tract and the human brain, lungs, liver, and other organs, for example. Now scientists have revealed yet another way that gut microbes can influence human health. Reporting in Nature Microbiology, scientists have shown that gut bacteria can send proteins directly into human cells, which can affect immune reactions.
In this work, scientists showed that many types of bacteria carry tools known as type III secretion systems, which can be used like syringes to deliver proteins into cells. It was previously thought that only pathogenic microbes carried these type III secretion systems.
"This fundamentally changes our view of commensal bacteria," said corresponding study author Professor Pascal Falter-Braun, Director of the Institute for Network Biology at Helmholtz Munich. "It shows that these non-pathogenic bacteria are not just passive residents but can actively manipulate human cells by injecting their proteins into our cells."
The researchers mapped over one thousand links between human proteins and bacterial effector proteins. This interaction map revealed that bacterial proteins like to target pathways in human cells that are related to immunity and metabolism.
Additional work showed that bacterial proteins can influence certain immune signaling pathways and molecules, such as NF-κB or cytokines, which can orchestrate immune responses.
Doe example, a molecule known as cytokine tumor necrosis factor (TNF) is a commonly used as a treatment for the chronic gut inflammation disease called Crohn’s.
Genes that encode for bacterial effector proteins were also found to be highly active in the gut microbiomes of Crohn's disease patients. This could indicate that gut bacterial proteins may contribute to chronic inflammation in the gut.
Though additional research will be needed, this could help open up new treatment options for the prevention or treatment of chronic disease. It also sheds new light on how gut microbes can directly influence human health.
Sources: Helmholtz Association of German Research Centres, Nature Microbiology