​Bacteria Have Been Hacking Your Genes Since Before You Were Born

Got your mother's smile? You might want to thank bacteria.

If you took high school biology, you know that we inherit traits like eye color and height from our parents' DNA. But human genes aren't all that's in the family bloodline. New research shows that mom also passes us bacteria, and we inherit traits from them, too.

In a study published in Nature, scientists at Washington University School of Medicine in St. Louis show that a "heritable trait" isn't always as it seems. The research, conducted in mice, shows how a bacterium that influences immunity can be passed from mother to offspring in the same manner that traits are inherited from parental DNA.

If the findings apply to humans, it would mean that microbes are hacking your genetic code, and that they've been doing it since before you were born.

"We may need to substantially expand our thinking about bacterial contributions, and perhaps the contributions of other microorganisms, to genetics and heredity," senior co-author Herbert W. Virgin IV said in a statement.

Meanwhile, we can all add the century-old model of genetic inheritance to the list of stuff we learned in high school that's not entirely true.

With the advent of high-throughput DNA sequencing, we've been confronted with a stark truth: Our planet is a hypochondriac's nightmare. From ocean floors to fast food restaurants, bacteria dominate every stretch of real estate they can—including us. In our own bodies, bacterial cells outnumber us ten to one. They impact our digestion, our immune system, perhaps even our personalities.

But until now, we've been able to draw a firm line in the sand between ourselves and our microbial consorts: Geneticists call it nature versus nurture. Our genes, the chemical blueprints we inherit from our parents, are locked safely away within the nuclei of our cells. Then there's our environment—everything else. The person you become depends on both.

Until now, bacteria have always landed firmly on the 'environment' side of the equation. They're something we pick up after we enter the world, not something we inherit.

As often happens in science, it was defective experiments that ultimately revealed to researchers how wrong our worldview was. In this case, the problem started with lab mice. In biomedical research, it's common practice to use bioengineered mice to study a particular gene in isolation. But sometimes, a mouse with a new trait—one that the humans didn't encode—would suddenly emerge.

That's what happened to a group of mice which, researchers discovered, were producing unusually low levels of IgA, an antibody linked to gastrointestinal disorders. There wasn't anything suspect in their DNA, but nonetheless, the defective trait seemed to be passing from mother to offspring. Eventually, the researchers pinpointed a culprit: The bacterium Sutterella, which was present in all low-IgA mice. While the bacterium probably entered the mouse colony by infecting a resident, it was now being passed on in a hereditary manner.

According to the authors, this means we need to consider a new factor—the DNA of microbes passed from mother to child—to understand how genes influence health.

Of course, this is mice we're talking about, not humans. But there's no obvious reason the same phenomenon shouldn't occur in us. Indeed, we already knew that mothers pass their babies a host of microbes during birth and breastfeeding, and that these critters can impact our health. It's not such a stretch, then, to imagine that we start getting bombarded with bugs a little earlier still.

Try not to let it bother you that a bacterium might be partially to blame for your off-center nose or your addiction to chocolate. In the future, we might use bacteria to hack all sorts of new traits into ourselves, like diet coke-flavored gentials or photosynthetic skin patches. Perhaps this is a sign that biohackers are on the right track after all.

Or that nature's just as crazy as we are.