There's a Bunch of Bacteria Having 'Sex' in Your Gut, And It's Wilder Than We Thought


A tiny orgy has taken over the human stomach. To live, the microorganisms in our digestive tract engage in regular'sex' with one another, all in the name of exchanging secrets on how to withstand lethal dosages of antibiotics.

Researchers from the University of Illinois at Urbana-Champaign and the University of California, Riverside have discovered novel interactions that go beyond what we previously known about this bacterial bump-and-grind.

Of course, bacteria lack genitals, but in biology,'sex' refers to any procedure that involves the exchange of genetic material.

A germ may transmit its DNA to another microbe in our gut by creating a 'temporary marriage' with another bacterium - it doesn't have to be the same species. 

When the microbe is ready, it simply sticks out a tube called a pilus and attaches itself to another cell, releasing a transportable bundle of DNA called a mobile genetic element.

Bacterial sex was discovered more than 70 years ago, when scientists determined that horizontal gene transfer was the mechanism by which germs shared antibiotic resistance genes, hence expanding antibiotic resistance. 

Bacterial sex doesn't simply happen when germs are attacked, as has recently been discovered. It happens all the time, and it's most likely one of the factors that keeps our microbiome in good shape.

New study has discovered which genes bacteria truly share when they do this. 

The research focused on the Bacteroidetes phylum of gut microorganisms, which account for up to 80% of the human microbiome and are essential digesters. 

"Without these bacteria, the huge, lengthy molecules from sweet potatoes, beans, whole grains, and vegetables would flow right through our systems," says scientist Patrick Degnan of the University of California, Riverside. 

"They break them down so we can use the energy."

However, in order to colonize the human stomach and assist in the digestion of carbohydrates, these bacteria must compete for limited resources in the large intestine. Vitamin B12 and other similar chemicals are examples of such resources, as they aid in the bacteria's metabolism and protein production. 

Because most gut microorganisms lack the capacity to generate these essential substances on their own, they must rely on what they can get from their surroundings. 

It helps to have genes for an efficient vitamin B12 transport mechanism on hand for this to work.

Researchers have now found B12 transporters that are transferred via bacterial sex in both petri dishes and vivo mouse models. 

"This discovery excites us because it demonstrates that this mechanism isn't just for antibiotic resistance," explains Degnan. 

"Anything that boosts a microbe's capacity to survive, including exchanging [genes for the transport of] vitamin B12, is presumably employed for horizontal gene exchange across microorganisms." 

Researchers discovered that when two gut microorganisms were put on a lab dish, the bacterium that couldn't produce B12 transport systems linked with the bacterium that could. The'receiving' bacteria could unload its valuable payload after the sex pilus crossed the space between the two.

Researchers studied the genome of the receiving bacteria, which was still alive, after the procedure and discovered that it had integrated an additional band of DNA from the donor. 

Something similar appears to occur with live mice. After giving a mouse two types of Bacteroidetes, one with the genes for transferring B12 and the other without, researchers discovered that the genes of the former had 'jumped' to the genes of the latter after five to nine days. 

Degnan explains, "It's like if two humans had sex and now they both have red hair."

The scientists point out that a second round of gene transfer, which took place between Bacteroidetes of the same species, was slightly faster than the first round, which took place between two distinct species. 

The findings show that when it comes to bacterial sex, there may be a slight'species barrier.' Although, unlike mammals, where a species may only reproduce with another of its kind, there is no such barrier. 

Bacteria, it appears, aren't nearly as choosy about their mates as we are, and our stomachs thank them for it.

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