Even if you’re alone this Valentine’s Day, there’s no need to worry: some parts of your body will be getting plenty of action. In fact, your body will host a veritable carnival of the sensual in your tummy, as your microbiota will engage in an orgy of sex and swinger’s parties — where they’ll be swapping genes instead of keys.

The salacious gene

Imagine you have a severe disease with a very unusual cure: you can treat by making love with someone who then passes on the necessary genes to cure your ailment. It is, as they say, sexual healing. Using sex to protect or heal themselves is precisely what bacteria can do, and it’s a crucial defense mechanism.

In the past, the research community thought bacterial sex (or conjugation, as scientists call it) was a terrible threat for humans, as this ancient process can spread DNA capable of conveying antibiotic resistance to their neighbors. Antibiotic resistance is one of the most pressing health challenges the world is facing, being projected to cause 10 million deaths a year by 2050.

But there’s more to this bacterial sex than meets the eye. Recently, scientists from the University of Illinois at Urbana-Champaign and the University of California Riverside witnessed gut microbes sharing the ability to acquire a life-saving nutrient with one another through bacterial sex. UCR microbiologist and study lead Patrick Degnan says:

“We’re excited about this study because it shows that this process isn’t only for antibiotic resistance. The horizontal gene exchange among microbes is likely used for anything that increases their ability to survive, including sharing vitamin B12.”

For well over 200-years, researchers have known that bacteria reproduce using fission, where one cell halves to produce two genetically identical daughter cells. However, in 1946, Joshua Lederberg and Edward Tatum discovered bacteria could exchange genes through conjugation, an entirely separate act from reproduction.

Conjugation occurs when a donor and a recipient bacteria sidle up to each other, upon which the donor creates a tube, called a pilus that attaches to the recipient and pulls the two cells together. A small parcel of DNA is then passed from the donor to the recipient, providing new genetic information through horizontal transfer.

Ironically, it wasn’t until Lederberg met and fell in love with his wife, Esther Lederberg, that they made progress regarding bacterial sex.

Widely acknowledged as a pioneer of bacterial genetics, Esther still struggled for recognition despite identifying the horizontal transfer of antibiotic resistance and viruses, which kill bacteria known as bacteriophages. She discovered these phages after noticing small objects nibbling at the edges of her bacterial colonies. Going downstream to find out how they got there, she found these viral interlopers hiding dormant amongst bacterial chromosomes after being transferred by microbes during sex.

Later work found that environmental stresses such as illness activated these viruses to replicate within their hosts and kill them. Still, scientists assumed that bacterial sex was purely a defense mechanism.

Promiscuity means longevity

The newly-published study builds on Esther’s work. The study authors felt this bacterial process extended beyond antibiotic resistance. So they started by investigating how vitamin B12 was getting into gut microbial cells, where the cells had previously been unable to extract this vitamin from their environment — which was puzzling as, without vitamin B12, most types of living cells cannot function. Therefore, many questions remained about how these organisms survived without the machinery to extract this resource from the intestine.

The new study in Cell Reports uses the Bacteroidetes species, which comprise up to 80% of the human microbiome in the intestines, where they break down complex carbohydrates for energy.

“The big, long molecules from sweet potatoes, beans, whole grains, and vegetables would pass through our bodies entirely without these bacteria. They break those down so we can get energy from them,” the team explained.

This bacteria was placed in lab dishes mixing those that could extract B12 from the stomach with some that couldn’t. The team then watched in awe while the bacteria formed their sex pilus to transfer genes enabling the extraction of B12. After the experiment, researchers examined the total genetic material of the recipient microbe and found it had incorporated an extra band of DNA from the donor.

Among living mice, something similar happens. When the group-administered two different subgroups of Bacteroidetes to a mouse – one that possessed the genes for transferring B12 and another that didn’t — they found the genes had ‘jumped’ to the receiving donee after five to nine days.

“In a given organism, we can see bands of DNA that are like fingerprints. The recipients of the B12 transporters had an extra band showing the new DNA they got from a donor,” Degnan said.

Remarkably, the team also noted that different species of phages were also transferred during conjugation, exhibiting bacterial subgroup specificity in some cases. These viruses also showed the capacity to alter the genomic sequence of its bacterial host, with the power to promote or demote the life of its microbic vessel when activated.

Sexual activity in our intestines keeps us healthy

Interestingly, the authors note they could not observe conjugation in all subgroups of the Bacteroidetes species, suggesting this could be due to growth factors in the intestine or a possible subgroup barrier within this large species group slowing the process down.

Despite this, Degnan states, “We’re excited about this study because it shows that this process isn’t only for antibiotic resistance.” And that “The horizontal gene exchange among microbes is likely used for anything that increases their ability to survive, including sharing [genes for the transport of] vitamin B12.”

Meaning that bacterial sex doesn’t just occur when microbes are under attack; it happens all the time. And it’s probably part of what keeps the microbiome and, by extension, ourselves fit and healthy.