10 Mysteries of the Human Microbiome Revealed

Written by Jordan Rosenfeld
Image Credit: ISTOCK

You may think of your body as home to only one organism: you. But you actually host trillions of microbes, mainly bacteria, fungi and viruses, comprising their own individual microbiomes—ecosystems—too small to be seen with the naked eye.

Before you rush off to take a shower, consider that these living colonies in your body work in synergy with you to keep you healthy. Studying them can reveal imbalances in health, and offer avenues of treatment for a wide range of physical and mental health problems. Your microbiome is so unique to you, it could one day replace the fingerprint ID. And when artists interpret this amazing world, the results can be simply beautiful. Here are 10 mysteries revealed about the human microbiome.

1. YOU ARE MORE BACTERIA THAN HUMAN. 

Bacterial cells are so prolific in our bodies, that they outnumber our human cells 10 to 1. It’s only because they’re so microscopically tiny that we don’t notice their presence.

2. YOUR THROAT MICROBIOME MIGHT REVEAL IF YOU ARE LIKELY TO DEVELOP SCHIZOPHRENIA.

A recent study done at George Washington University found a notable difference in the throat microbiomes of schizophrenics as compared to healthy controls. In particular, they found high levels of lactic-acid bacteria and “an increased number of metabolic pathways related to metabolite transport systems including glutamate, and vitamin B12.” While there is much more research to be done, this information has potential applications for biomarkers that could detect and diagnose schizophrenia with a simple swab test, possibly before symptoms occur.

3. YOUR GUT MICROBIOME AFFECTS YOUR MOOD. 

Several studies have tested the effects of bacteria lactobacillus and bifidobacterium on mice and humans. In one study, mice fed these bacteria showed less anxiety or despair (measured by how willing mice are to rescue themselves when dropped into jars of water), which they compared to how mice behaved when given the anti-depressant drug Prozac. In another study, mice treated with the probiotics performed better on cognitive tests, including navigating mazes, and object recognition tests. And in the biggest known human study, a group of 25 healthy women ate yogurt with live bacteria every day for four weeks. Compared to the control group, the yogurt eaters had “calmer” reactions to images of facial expressions. Researchers are still trying to pinpoint how these good bacteria improve the mood; theories include activating compounds like serotonin, stimulating the vagus nerve, which releases the natural calming agent acetylcholine, and simply sending calming signals to the immune and nervous systems. Researchers hope that one day common psychiatric disorders could be treated with probiotics as well as drugs.

4. THE MICROBIOTA OF YOUR SKIN HELP PROTECT AGAINST INVADERS. 

The exterior surface of human skin is home to as many as 300 strains of bacteria. These microbes are intricately linked to your immune system, helping you defend against invading pathogens. While their intentions aren’t selfless—they are, after all, protecting their home—you receive multiple benefits: helping you heal wounds, control skin inflammation, and modulate T cells and interleukin-1, key compounds that fight infection, according to theNational Human Genome Institute.

5. GREATER BACTERIAL BIODIVERSITY IS LINKED TO LOWER ALLERGIES.

If you’re looking for another reason to clean your house less often, more research points to allowing for more bacterial diversity in your home, and connects a reduction in bacterial biodiversity to an increase in allergies. Chemicals that clean floors and toilets also kill good bacteria—better to use “natural” agents like baking soda and vinegar, or to stress less over a slightly dirty floor, the dog sleeping on your bed, or using hand sanitizer for dirty hands. Other research suggests that reduced interaction with the natural world is also responsible for a rise in allergies. So go for a hike, and get dirty.

6. YOU HAVE BACTERIA DNA IN YOUR GENES. 

According to a study done by the University of Cambridge, as many as 145 of the genes in your human genome are bacteria genes that have used a process known as horizontal gene transfer to "jump" into human DNA over the course of our evolution.

7. YOUR DOMINANT HAND HOSTS DIFFERENT BACTERIA THAN YOUR NON-DOMINANT HAND.

Though you have approximately the same number of bacteria on each of your hands, research done at George Washington University has found that the colonies are different from hand to hand, suggesting that your dominant hand, with which you are likely to do more things, comes in contact with a different set of bacteria than the other hand.

8. BACTERIA HAVE GENDER PREFERENCES.

Men always take heat for being dirtier than women, but it might be true, in a way. At the very least, the bacteria Corynebacterium—usually found in the armpit and responsible for the pungent odor—prefers male chemistry. It's 80 percent more abundant on male skin than on female skin, according to a study published in the journal PNAS.  But Enterobacteriales is 400 percent more abundant on women, and Lactobacillaceae (primarily found in the mouth and the vagina) is 340 percent more abundant. In general, the palms of women were found to have greater bacterial diversity than the palms of men. Some explanations for this diversity may have to do with the slightly different Ph balance between male and female skin, differences in sweat and sebum (oil) production, and the frequency of moisturizer or cosmetics use.

9. YOUR BELLY BUTTON HAS ITS OWN MICROBIOME.

There are more than 1400 strains of bacteria that call your "inny" home, with as many as 662 of those not previously identified by science until the Belly Button Biodiversity Projectanalyzed them. And in case you were wondering, "outies" are the same.

10. YOUR FIRST MICROBIOME CONTACT WAS IN UTERO. 

For years, science considered the uterus of a pregnant woman a sterile environment, but new research published in Science Translational Medicine revealed that placentas have a unique microbiome that is different from any other part of the body (though most similar to the microbiome of the mouth). Contact with their mothers’ placentas, and the umbilical cord that attaches them, offers babies their first exposure to the bacteria that will soon colonize and support their own small bodies. Understanding this particular microbiome may also help researchers learn more to treat in utero infections and preterm births.

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