It turns out that fluids aren’t the only thing we’re swapping with our bedtime mates. New research out this week shows that people also leave behind remnants of their genitals’ unique microbiome post-sex, a.k.a. their “sexome.”
Researchers at Murdoch University in Australia led the study, which aimed to test whether our microbiomes—the neighborhoods of bacteria that live in or on our bodies—could be a viable marker for forensic crime investigation. Using genetic sequencing, they were able to reliably identify traces of people’s genital bacteria transferred onto their partner following coitus. It’s a fascinating finding, but the resulting technique could someday be refined into a new tool for solving sexual assault cases, the researchers say.
Whether we like it or not, our bodies are teeming with bacteria, including in our downstairs junk. Fortunately, these bacteria are (usually) harmless and often vital to the body’s normal functioning. Many scientists have focused on studying how our microbiomes influence our health (particularly in the gut), but the Murdoch researchers wanted to see if the unique composition of each person’s passenger bacteria could be leveraged into a method for forensic identification, particularly the microbes that call our genitals home.
They’ve coined the neighborhoods of bacteria living on our penises or vaginas as the “sexome.”
“In forensic science we work on the concept that all contact leaves a trace behind. With fingerprints that’s obviously the residues from our skin and in the case of the sexome, we’re using the healthy bacterial communities living on, and within, our bodies as a means of detecting that transfer,” senior researcher Brendan Chapman, a forensic scientist at Murdoch, told Gizmodo.
Scientists often examine the make-up of microbiomes by genetically sequencing a particular segment of ribosomal RNA called 16S. Historically, scientists have only been able to read (and put back together) short lengths of 16S at a time, which allows them to tell apart broad groups of bacteria from one another. But nowadays, the technology has progressed enough that scientists like Chapman can identify these bacteria more clearly.
“We now have more advanced systems for massively parallel sequencing that can analyze longer strings of that 16S gene region, meaning we have a better view of the unique signatures within the community,” he explained. “It’s a bit like the difference between only knowing the names of chapters within a book, compared to being able to read the words on the page.”
Chapman and his team’s latest study, published Wednesday in the journal iScience, involved 12 monogamous, heterosexual couples. The couples had their baseline sexomes sequenced (using swabs collected from their genitals), were asked to abstain from sex for different lengths of time (two to 14 days), and then to have sex again, after which their sexomes were reanalyzed.
“What we found was that there were unique DNA sequence variants from the female that we could identify on the male, and vice versa,” Chapman said.
Factors like pubic hair or whether the man was circumcised didn’t seem to affect how easily sexomes were transferred between partners. Condom use (practiced in three of the couples) did affect these transfers, with most of the swapped bacteria now coming from the woman to the man. But that still suggests that scientists can use this method to identify men who potentially committed sexual assault, even when the person used a condom.
It will take time and more research to know whether our sexomes can truly become the next frontier of forensic investigation. The researchers note that menstruation appeared to change the makeup of a woman’s microbiome, for instance, so scientists will need to better understand and map these changes to account for that. Other important questions, such as how long it will take for people’s swapped bacteria to become untraceable with testing, are still unanswered.
But Chapman and his team, including lead researcher Ruby Dixon, who is pursuing a PhD based on this research, are hopeful about their work’s potential.
“It’s early days, and there is still a lot of work to do before this is fit for use in legal proceedings, but we have confidence that in the future, sexome analysis will be another tool in the forensic DNA toolkit that can help identify perpetrators of sexual assault,” Chapman said.
And even beyond the crime-solving applications, simply knowing more about our sexomes is important.
“More generally speaking, the greater our understanding of the relationship we have with our bacterial passengers on our bodies, the better we can utilize them for improving health outcomes also. We already know how important the gut microbiome is to digestive health, and the same is likely true for the sexome—providing protective features for the vaginal microenvironment and maybe even fertility,” Chapman added.