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Arthur T Knackerbracket has found the following story:

Inside your gut, a quiet battle is raging among many bacteria competing for survival. A new study suggests how some gut bacteria might acquire a defensive arsenal against a type of toxic assault waged by their neighboring microbes.

Researchers at the University of Washington wanted to understand what forces drive the composition and ecology of the microbe collections that live in people's guts. The state of the human gut microbiome is critical to aspects of health and disease.

"Diet and immune response are not enough to explain the constituents of their gut microbiome," the project scientists said. The victors of struggles and hostilities among micro-organisms attempting to reside in the gut may contribute to the makeup of that microbial community.

[...] Bacteria have many ways of antagonizing their own or other species, these scientists noted. A group of prevalent gut bacteria, from the order Bacteroidales, have a secretion mechanism to inject toxic proteins into bacteria that crowd too close. At the same time, they keep themselves safe from their own or their kin cells' poisons by carrying specific immunity factors that neutralize the toxins.

In the current study, the researchers found that several of the Bacteroides species that populate the human gut have acquired sizable interbacterial defense gene clusters. These encode for large arrays of immunity determinants that neutralize the direct hit of toxins from their competitors. The clusters have features that suggest they are actively acquiring new immunity genes as new threats are encountered.

[...] Based on their observations, the scientists think these immunity genes have an adaptive role because they help these bacteria overcome toxic hits from their B. fragilis assailants. They see this shielding effect during growth in Petri dishes in their labs and when they introduced the bacteria carrying these genes into the guts of mice.

The researchers then asked if similar orphan immunity genes protect against other toxins produced in the gut, in addition to those delivered by B. fragilis. This led to the discovery of a second set of orphan immunity gene clusters that are widespread among Bacteroides species in the gut. These clusters contain genes predicted to guard against diverse toxins made by a range of different species, not just other Bacteroides. A second striking feature of this second kind of immunity gene cluster is that it shows signs of recent new gene acquisition.

The scientists concluded that obtaining and maintaining orphan immunity genes clusters is a common way for gut bacteria to try to fend off interbacterial assaults and sustain their species' or strain's presence in the human gut microbiome.

Journal Reference:

Benjamin D. Ross, Adrian J. Verster, Matthew C. Radey, Danica T. Schmidtke, Christopher E. Pope, Lucas R. Hoffman, Adeline M. Hajjar, S. Brook Peterson, Elhanan Borenstein, Joseph D. Mougous. Human gut bacteria contain acquired interbacterial defence systems^[$]. Nature, 2019; DOI: 10.1038/s41586-019-1708-z

Original Submission