One bacterium sticks out of the hairs and connects to another (Image: UCR)
The microbes in our gut have regular "sex," which in a way is a good thing for both bacteria and us.
Written by | Twenty-seven
Review | chestnut
As you probably know, in our gut, there are a lot of bacteria living there. What you may not know is that in order to survive better, these bacteria will have "sexual activity" on a regular basis.
Wait, bacteria don't seem to have genitalia in the strict sense of the word, and there is no sex division, so can they have sex?
We have the impression that bacteria multiply by dividing, and there is no such "worldly annoyance" as mating. But under the biological definition, the essence of sex is the process of exchanging genetic material. A recent study published in The Cell Report showed that bacteria in our gut can stick out a tube called pilus and "inject" their DNA into another bacterium, helping other bacteria have the ability to get vitamin B12. For these seemingly simple life forms, although it has nothing to do with the reproductive process, this is their "sex life".
The "sexual life" of bacteria
In fact, bacteria also have a "sexual life", which scientists have discovered very early. In 1946, Edward Tatum and Joshua Lederberg first discovered that there was also an exchange of genes between bacteria.
By chemical induction, Tatum and Lederberg acquired two mutants of the Escherichia coli K12 strain. Neither mutant can synthesize certain essential nutrients, so they cannot survive in their natural environment and can only grow in a laboratory environment that provides the corresponding nutrients. However, the nutrients they cannot synthesize are not the same.
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 deliver genetic material to other bacteria, a process That Ledberg calls "conjugation."
The discovery quickly shocked the genetics community and led Lederberg to share the 1958 Nobel Prize in Physiology or Medicine. Today, we know more details about this process: there is a special class of fungus on the surface of the bacteria, which are like tubes. It uses this hair to attach itself to another bacterium and shoots out a "packed" piece of DNA, the plasmid. In this way, different bacteria, and even bacteria of different species, can "share" genetic material.
Even the ability to grow hairs spreads through this method. E. coli grows hair by relying on the F plasmid (F plasmid) in the body, and the E. coli that can grow the hair will engage bacteria that do not have this ability, and let one of the chains of the double-stranded F plasmid transfer to another bacteria through the hair channel, and then synthesize complementary chains. In this way, the bacteria on the receiving side can also grow hairs and turn around and become the new supplier.
Through the bonding process of the hairs, other bacteria can also acquire the ability to grow hairs (Credit: Adenosine - Own Work, CC BY-SA 3.0)
However, it is worrying that in addition to the genes related to hair formation, there are a large number of antibiotic resistance genes transferred through the hairy channel. Scientists soon realized that in this way, bacteria could "take" the resistance genes of other bacteria for themselves, helping themselves to avoid antibiotic attacks. This has also become a major cause of the widespread spread and persistence of drug resistance in bacteria.
Looting the "corpses" of their companions
For bacteria, bonding isn't even the only way to get DNA: in addition to getting DNA from a living partner, they can also "rob" the "corpse" of other bacteria from outside the body.
When bacteria die, they crack and release DNA from the body, which becomes a "treasure trove" for other bacteria. In 2018, researchers at Indiana University recorded Vibrio cholerae sticking out of the hairs, hooking a piece of DNA and bringing it back to the body.
The green hairs are like a tentacle that "grabs" the red DNA and drags it back into the body. (Image source: Ankur Dalia/Indiana University)
The fungus is an extremely slender structure, only one-ten-thousandth the size of a human hair. In order to see these subtle structures, the researchers specially developed a unique dye to help bacteria "dye the hairs green." Under the microscope, the green hairs resemble a tentacle that "grabs" the red DNA and drags it back into the body. "It's like threading a needle." Courtney Ellison, the study's lead author, said that it is estimated that the pores through which DNA passes may be only 7-8 nm in diameter, and the DNA that is caught is about 50 nm long, "If it were not for these hairs, the chances of DNA naturally entering the bacteria through this pore can be said to be minimal." ”
Bacteria that seem quiet under a normal microscope are actually stretching their hairs. (Image source: Ankur Dalia/Indiana University)
Intestinal bacteria aid digestion
Speaking of which, you might find bacteria scheming. But in fact, these shared behaviors of bacteria are only for better survival, and this is not necessarily all bad news for humans.
In the latest study, published in The Cell Report, the researchers paid special attention to bacteria from the Bacteroidetes phylum. Bacteroides are important members of the human gut microbiome, and in some people, even 80% of the entire microbiome. These bacteroides are the main metabolizers of dietary polysaccharides, "without them, you can't digest the big, long molecules in foods like sweet potatoes, legumes, vegetables, etc." They break down these foods so that we can get energy from them. Patrick Degnan, the paper's first author, explained it this way.
In the normal human microbiome, Bacteroides can make up to 30% of bacteria (Image: NOAA/OpenStax Microbiology)
However, it is not easy to settle in the human gut and (by the way) help us digest carbohydrates. To do this, 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 both bacterial metabolism and protein synthesis. The problem is that most microbes in the gut — including most Bacteroides — don't have the ability to synthesize B12 and related compounds on their own, which means they need to have efficient transport systems in place to absorb B12 from the environment.
That's when sharing between bacteria comes in handy: The researchers found that bacteria from the Bacteroides phylum also share genes related to the B12 transporter by joining.
B12 transporter
Before formally conducting the study, Degeninand and colleagues identified an important transporter protein responsible for helping gut microbes absorb B12. Then, Degennan began to think, how do these microorganisms obtain the B12 transporter? Is this process also related to the bonding of bacteria?
To prove this suspicion, Degennan and the research team will culture bacteria that can absorb B12 together with bacteria that cannot absorb B12, just like Ryderberg's experiment more than 70 years ago. After some time, the bacteria that could not absorb B12 survived and gained the ability to absorb B12.
To determine the origin of this gene, the researchers examined the entire genome of the bacteria. "To a given organism, their DNA bands are like fingerprints. Apparently, recipients of the DNA have integrated an extra piece of DNA from the donor, showing that they got new DNA from the donor. Degennan said.
Experiments in mice yielded similar results, when the researchers transplanted two Bacteroides (one that transports B12 and the other cannot) into the intestines of mice, and only 5-9 days later, the genes of the former "jumped" into the latter. "It's the equivalent of two people [with different hair colors] having sex, and now they both have red hair." Degennan said.
Another interesting new finding is that the paper notes that gene transfer between the same species is slightly faster than between two different species, suggesting that even bacterial sexuality may have a slight "reproductive isolation." However, compared to most eukaryotes, this sexual behavior is still much "wild".
Reference Links
[1]https://www.sciencealert.com/there-are-a-bunch-of-bacteria-having-sex-in-your-gut-right-now
[2]https://news.ucr.edu/articles/2022/02/01/human-gut-bacteria-have-sex-share-vitamin-b12
[3]https://www.nature.com/articles/35084593
[4]https://www.statnews.com/2018/02/20/antibiotic-resistance-bacterial-sex/
[5]https://www.nobelprize.org/prizes/medicine/1958/ceremony-speech/
[6]https://profiles.nlm.nih.gov/spotlight/bb/feature/bacgen1
Related Papers:
https://journals.asm.org/doi/full/10.1128/mBio.01305-14