The gut microbiome is very diverse, and microorganisms do not live in harmony
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Your gut is a battlefield where rival tribes of bacteria armed with poison darts fight for territory. And these battles are often won by traitorous armies who have been turned over by the selfish DNA transferred by their enemies.
“The human colon is one of the most dense microbial ecosystems on Earth,” says Laurie Comstock of the University of Chicago in Illinois. There are many different species of bacteria, and different strains within a species competing for the same resources.
In order to gain an advantage, many people try to poison their rivals by releasing toxins. Some are equipped with even more unusual weapons, dart guns that fire high-velocity syringes to inject poison directly into other bacteria or nearby large cells.
“They’re spring-loaded weapons and require the creature to get very close,” Comstock said.
The innocuous-sounding name for this type of dart gun is the Type 6 Secretion System, or T6SS. Different species are armed with darts, and there are many variations in how they work. For example, darts can contain various toxins.
But how does a blind germ avoid shooting not only enemies but also friends? Not so. Some species fire poisoned arrows as quickly as possible, attacking enemies and allies alike.
But importantly, the genetic instructions for making a particular type of dart gun are always accompanied by instructions for making an antidote to the poison in the darts fired from that gun. If a bacterium is attacked by an arrow from a member of the same tribe, it will not be harmed.
In other words, in this world of poison darts and antidotes, which side a bacterium takes is determined by what darts and antidotes it produces.
In this world of insects, one of the deadliest is a species called the . Bacteroides fragiliswhich releases various poisons as well as fires darts non-stop. B. fragilis Because Comstocks feed on complex sugars in the mucus lining of their intestines, they believe the reason for their aggression is because they hijack the mucus lining to protect themselves from other related species.
But some of these other species possess extraordinary weapons in the form of selfish fragments of DNA that behave almost like independent entities. One of these pieces of DNA, called GA1, encodes a gene for the machinery that allows GA1 to transfer copies of itself to other bacteria.
It also carries genes for dart guns and antidotes to dart gun poison. The Comstock team has shown that when GA1 enters; B. fragilissomehow blocking production. B. fragilis Develop guns and have them start manufacturing GA1 guns, essentially making them traitors.
When these bacteria multiply, they form an army of traitors that can kill people B. fragilis What GA1 is missing. In numerous tests, Comstock’s team found that the traitor forces usually won these battles.
But in our guts, where many other species and toxins are present, the results may be different, she says. “There are so many things to consider in these battles,” Comstock said. “There’s not always a clear winner.”
Her team also discovered another piece of selfish DNA called GA2. This seems to work similarly to GA1, but with a different dart gun and antidote.
“Side switches may be more common than we realized,” says Brian Hamer of the Georgia Institute of Technology in Atlanta.
The bacterium that causes cholera also constantly produces and fires dart guns. This move has been considered costly, but last year Hammer’s team cholera bacteria Firms that do not generate T6SS grow almost no faster than firms that do. This suggests that the cost of moving while firing a gun is surprisingly small.
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