"sex" is secretly taking place in your intestines.

The microbes in our gut have "sex" on a regular basis, which is good for both bacteria and us.

As you may know, there are a lot of bacteria living in our intestines. What you may not know is that in order to survive better, these bacteria have "sex" on a regular basis.

Wait, wait,

In our impression, bacteria reproduce by division, and there is no "secular worry" such as mating. But according to the definition of biology, the essence of sex is the exchange of genetic material. Recently, a study published in the Cell report shows that bacteria in our gut can stick out a tube called pilus and "inject" their own DNA into another bacteria, helping other bacteria to acquire vitamin B12. For these seemingly simple life forms, although they have nothing to do with the reproductive process, this is their "sex life".

The "sex life" of bacteria

In fact, bacteria also have a "sex life", scientists discovered a long time ago. In 1946, Edward Edward Tatum and Joshua Lederberg first discovered that there was also an exchange of genes between bacteria.

Tatum and Ledberg obtained two mutants of Escherichia coli (Escherichia coli) K12 strain by chemical induction. Neither of the two mutants could synthesize some necessary nutrients, so they could not survive in the natural environment and could only grow in the laboratory environment where the corresponding nutrients were provided. However, they cannot synthesize different nutrients.

After culturing the two mutants together for a period of time, some of the offspring of E. coli regained the ability to synthesize these nutrients. After a series of experiments ruled out other possibilities, the researchers concluded that E. coli can pass genetic material to other bacteria, a process Ledberg calls "conjugation."

The discovery quickly shocked genetics and allowed Ledberg to share the 1958 Nobel Prize in physiology or medicine. Now, we know more details about this process: there are special tube-like fimbriae on the surface of bacteria. It uses this fimbriae to attach itself to another bacteria and emit a "packaged" DNA-- plasmid. In this way, different bacteria, even different species of bacteria, can "share" genetic material.

Even the ability to grow fimbriae spreads in this way. E. coli grows pili on the F plasmid in the body. E. coli, which can produce fimbriae, conjugates with bacteria that do not have this ability, and transfers one strand of the double-stranded F plasmid to another bacteria through the pilus channel to synthesize complementary chains. In this way, the bacteria on the receiving side can also grow fimbriae and turn around to become a new supplier.

However, it is worrying that there are a large number of antibiotic resistance genes transferred through the pili channel, in addition to the genes related to the formation of fimbriae. Scientists soon realized that in this way, bacteria can "take" the resistance genes of other bacteria as their own, helping them avoid being attacked by antibiotics. This has also become the main reason for the widespread spread and persistence of drug resistance in bacteria.

Search for the "body" of a companion.

For bacteria, conjugation is not even the only way to get DNA: in addition to obtaining DNA from living partners, they can also "plunder" the "corpses" of other bacteria in vitro.

When bacteria die, they split apart and release their DNA, which becomes a "treasure" for other bacteria. In 2018, researchers at Indiana University recorded Vibrio cholerae (Vibrio cholerae) protruding fimbriae, catching a piece of DNA and bringing it back into the body.

The fimbriae is an extremely fine structure, only 1/10000 of the thickness of the hair. To see these subtle structures, the researchers developed a unique dye that helps bacteria "dye their fimbriae green". Under a microscope, the green fimbriae look like tentacles, grabbing the red DNA and dragging it back into the body. "it's like piercing a needle and thread." Courtney Ellison, lead author of the study, said it was estimated that the hole DNA passed through might be only 7-8nm in diameter, while the captured DNA was about 50nm long. "if it weren't for these fimbriae, the chances of DNA entering the bacteria naturally through this hole would be minimal."

Intestinal bacteria aid digestion

Speaking of which, you may think bacteria are scheming. But in fact, these shared behaviors of bacteria are only for better survival, and this is not necessarily all bad news for humans.

However, it is not easy to settle in the human gut and help us digest carbohydrates. To this end, these bacteria must compete with other microbes in the gut for limited resources, including vitamin B12 and related compounds.

Yes, your gut bacteria, like you, need vitamin B12, which plays a key role in bacterial metabolism and protein synthesis. The problem is that most microbes in the gut-including most bacteroides-do not have the ability to synthesize B12 and related compounds on their own, which means they need to prepare an efficient transport system to absorb B12 from the environment.

At this point, sharing between bacteria came in handy: the researchers found that bacteria in the phylum Bacteroides also share genes related to B12 transporters in this way.

B12 transporter

Before officially launching the study, Degennan and his colleagues identified an important transporter responsible for helping intestinal microbes absorb B12. Then Degennan began to think, how did these microbes get the B12 transporter? is this process also related to the binding of bacteria?

To prove this speculation, Degennan and the team will grow bacteria that can absorb B12 and bacteria that cannot, just as Ledberg did more than 70 years ago. After a period of time, bacteria that could not absorb B12 survived and gained the ability to absorb B12.

Similar results were obtained in mice. When the researchers transplanted two kinds of Bacteroides (one that can transport B12 and the other could not) into the intestines of mice, only 5-9 days later, the genes of the former "jumped" into the latter. "it's like two people [with different hair colors] had sex, and now they all have red hair." Degennan said.