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10 Mysteries of the Human Microbiome Revealed

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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 the researchers 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 the National 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 Project analyzed 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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Scientists Use a CT Scanner to Give Whales a Hearing Test
Ted Cranford
Ted Cranford

It's hard to study how whales hear. You can't just give the largest animals in the world a standard hearing test. But it's important to know, because noise pollution is a huge problem underwater. Loud sounds generated by human activity like shipping and drilling now permeate the ocean, subjecting animals like whales and dolphins to an unnatural din that interferes with their ability to sense and communicate.

New research presented at the 2018 Experimental Biology meeting in San Diego, California suggests that the answer lies in a CT scanner designed to image rockets. Scientists in San Diego recently used a CT scanner to scan an entire minke whale, allowing them to model how it and other whales hear.

Many whales rely on their hearing more than any other sense. Whales use sonar to detect the environment around them. Sound travels fast underwater and can carry across long distances, and it allows whales to sense both predators and potential prey over the vast territories these animals inhabit. It’s key to communicating with other whales, too.

A CT scan of two halves of a dead whale
Ted Cranford, San Diego State University

Human technology, meanwhile, has made the ocean a noisy place. The propellers and engines of commercial ships create chronic, low-frequency noise that’s within the hearing range of many marine species, including baleen whales like the minke. The oil and gas industry is a major contributor, not only because of offshore drilling, but due to seismic testing for potential drilling sites, which involves blasting air at the ocean floor and measuring the (loud) sound that comes back. Military sonar operations can also have a profound impact; so much so that several years ago, environmental groups filed lawsuits against the U.S. Navy over its sonar testing off the coasts of California and Hawaii. (The environmentalists won, but the new rules may not be much better.)

Using the CT scans and computer modeling, San Diego State University biologist Ted Cranford predicted the ranges of audible sounds for the fin whale and the minke. To do so, he and his team scanned the body of an 11-foot-long minke whale calf (euthanized after being stranded on a Maryland beach in 2012 and preserved) with a CT scanner built to detect flaws in solid-fuel rocket engines. Cranford and his colleague Peter Krysl had previously used the same technique to scan the heads of a Cuvier’s beaked whale and a sperm whale to generate computer simulations of their auditory systems [PDF].

To save time scanning the minke calf, Cranford and the team ended up cutting the whale in half and scanning both parts. Then they digitally reconstructed it for the purposes of the model.

The scans, which assessed tissue density and elasticity, helped them visualize how sound waves vibrate through the skull and soft tissue of a whale’s head. According to models created with that data, minke whales’ hearing is sensitive to a larger range of sound frequencies than previously thought. The whales are sensitive to higher frequencies beyond those of each other’s vocalizations, leading the researchers to believe that they may be trying to hear the higher-frequency sounds of orcas, one of their main predators. (Toothed whales and dolphins communicate at higher frequencies than baleen whales do.)

Knowing the exact frequencies whales can hear is an important part of figuring out just how much human-created noise pollution affects them. By some estimates, according to Cranford, the low-frequency noise underwater created by human activity has doubled every 10 years for the past half-century. "Understanding how various marine vertebrates receive and process low-frequency sound is crucial for assessing the potential impacts" of that noise, he said in a press statement.

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Women Suffer Worse Migraines Than Men. Now Scientists Think They Know Why
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Migraines are one of medicine's most frustrating mysteries, both causes and treatments. Now researchers believe they've solved one part of the puzzle: a protein affected by fluctuating estrogen levels may explain why more women suffer from migraines than men.

Migraines are the third most common illness in the world, affecting more than 1 in 10 people. Some 75 percent of sufferers are women, who also experience them more frequently and more intensely, and don't respond as well to drug treatments as men do.

At this year's Experimental Biology meeting in San Diego, researcher Emily Galloway presented new findings on the connection between the protein NHE1 and the development of migraine headaches. NHE1 regulates the transfer of protons and sodium ions across cell membranes, including the membranes that separate incoming blood flow from the brain.

When NHE1 levels are low or the molecule isn't working as it's supposed to, migraine-level head pain can ensue. And because irregular NHE1 disrupts the flow of protons and sodium ions to the brain, medications like pain killers have trouble crossing the blood-brain barrier as well. This may explain why the condition is so hard to treat.

When the researchers analyzed NHE1 levels in the brains of male and female lab rats, the researchers found them to be four times higher in the males than in the females. Additionally, when estrogen levels were highest in the female specimens, NHE1 levels in the blood vessels of their brains were at their lowest.

Previous research had implicated fluctuating estrogen levels in migraines, but the mechanism behind it has remained elusive. The new finding could change the way migraines are studied and treated in the future, which is especially important considering that most migraine studies have focused on male animal subjects.

"Conducting research on the molecular mechanisms behind migraine is the first step in creating more targeted drugs to treat this condition, for men and women," Galloway said in a press statement. "Knowledge gained from this work could lead to relief for millions of those who suffer from migraines and identify individuals who may have better responses to specific therapies."

The new research is part of a broader effort to build a molecular map of the relationship between sex hormones and NHE1 expression. The next step is testing drugs that regulate these hormones to see how they affect NHE1 levels in the brain.

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