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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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The Prehistoric Bacteria That Helped Create Our Cells Billions of Years Ago
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We owe the existence of our cells—the very building blocks of life—to a chance relationship between bacteria that occurred more than 2 billion years ago. Flash back to Bio 101, and you might remember that humans, plants, and animals have complex eukaryotic cells, with nucleus-bound DNA, instead of single-celled prokaryotic cells. These contain specialized organelles such as the mitochondria—the cell’s powerhouse—and the chloroplast, which converts sunlight into sugar in plants.

Mitochondria and chloroplasts both look and behave a lot like bacteria, and they also share similar genes. This isn’t a coincidence: Scientists believe these specialized cell subunits are descendants of free-living prehistoric bacteria that somehow merged together to form one. Over time, they became part of our basic biological units—and you can learn how by watching PBS Eons’s latest video below.

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11 Primal Facts About Dian Fossey
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Born in San Francisco on January 16, 1932, Dian Fossey came from a world far removed from the dense jungles of East Africa. She discovered that environment in her thirties and spent the final decades of her life studying the gorillas that lived there. From her groundbreaking primatology work to her mysterious death, here are 11 facts about the scientist behind Gorillas in the Mist.

1. HER LOVE OF ANIMALS BEGAN WITH A PET GOLDFISH.

Though she went on to become one of history's most famous animal-lovers, Fossey didn't grow up in a pet-friendly household. The only animal she was allowed to keep as a child was a single goldfish. She loved her fish, but when it died, her parents barred her from getting another animal to replace it. Even a pet hamster offered to her by a classmate was forbidden from entering the house.

2. SHE WAS A PRIZE-WINNING EQUESTRIAN.

Not permitted to keep pets in the home, Fossey nurtured her passion for animals through equestrianism. She received her first horseback-riding lesson at age 6. By the time she reached her teen years, she was advanced enough to merit an invitation to join the riding team at Lowell High School in San Francisco. Her hobby earned her several awards and pushed her to pursue an education in animal husbandry at the University of California, Davis. Even after she'd shifted career aspirations to occupational therapy, Fossey chose to move to Kentucky to be closer to farm life.

3. SHE SPENT HER LIFE SAVINGS ON HER FIRST TRIP TO AFRICA.

Dian Fossey was 31 when she first stepped foot on the continent where she'd complete her most important work. Inspired by a friend's trip to Africa, she collected her life savings (about $8000), took out a three-year bank loan, and planned a seven-week trip through the wilderness of Kenya, Tanzania, Congo, and Zimbabwe. On her adventures there she met Louis Leakey, the anthropologist famous for sponsoring the all-woman trio of primatology pioneers (the "trimates") that included Jane Goodall, Biruté Galdikas, and eventually Dian Fossey herself. It was also during this period when Fossey saw gorillas in the wild for the first time. She met wildlife photographers Joan and Alan Root and joined them on an expedition to photograph the animals in the Congolese mountains. The vacation wasn't scientific in nature, but as Fossey later wrote, "The seed was planted in my head, even if unconsciously, that I would someday return to Africa to study the gorillas of the mountains."

4. SHE PROVED HER DEDICATION WITH AN APPENDECTOMY.

Leakey reconnected with Fossey back in the States in 1966. The anthropologist had spent the last several years supporting his former secretary Jane Goodall in her chimpanzee research, and now he was in search of a candidate to do for gorillas what Goodall had done for chimps. After getting to know Fossey better, he decided she was the right woman for the job. He offered to gather the funding for her trip back to Africa, but before she left she would need to remove her appendix as a precaution. This didn't scare her off. When Leakey wrote six weeks later to say the surgery wouldn't be necessary and he had just wanted to make sure she was committed, she was already appendix-less.

5. HER FIRST RESEARCH EXPEDITION ENDED ABRUPTLY.

Fossey returned to the Congo toward the end of 1966—just months before a civil war erupted in the already volatile region. Rebel soldiers captured her at her base camp in July 1967. After spending two weeks in military detainment, she was able to bribe her way out with promises of cash and her Land Rover. The guards agreed to drive her to Uganda, and shortly after they arrived, she had them arrested. After the scare, Fossey was ready to resume her research almost immediately: This time she set up camp in Rwanda, ignoring warnings from the U.S. Embassy.

6. SHE UNCOVERED THE GORILLAS' TRUE NATURE.

Prior to Fossey's research, the public viewed gorillas as beasts similar in temperament to King Kong. She quickly disproved the notion that gorillas were bloodthirsty animals that would attack humans when given the chance.

To infiltrate their society, she adopted their habits. Walking on her knuckles and chewing on celery stalks allowed her to gain the apes' trust. As long as she maintained a nonthreatening profile and made her presence known at all times, she was safe around the gentle behemoths. Today we know that despite their intimidating size, gorillas are some of the least violent members of the great ape family.

7. SHE EARNED A UNIQUE NICKNAME FROM LOCALS.

Dian Fossey spent enough time at her research center in Rwanda to garner a reputation. To the locals she was Nyiramachabelli, a Swahili name that when roughly translated means "the woman who lives alone on the mountain."

8. SHE USED THE GORILLAS' NOSES TO TELL THEM APART.

Many of the gorillas Fossey studied were given names, such as Peanut, Rafiki, and Uncle Bert. Fossey used another method to tell her subjects apart: She drew sketches of their noses. Each gorilla has a unique pattern of wrinkles around its nose that makes it easy to identify. These nose prints are the equivalent of fingerprints in humans, but instead of getting up close to study them, Fossey was able to document them from far away using binoculars and a sketchpad.

9. ONE OF HER GORILLAS IS ALIVE TODAY.

Hundreds of gorillas made it into Dian Fossey's body of research. In 2017, only one specimen from that original pool is still alive. Poppy was born into a group of gorillas on Fossey's radar in 1976. The researcher documented the animal's birth and childhood in her journals. Today, at 41, Poppy is the oldest gorilla currently monitored by the Dian Fossey Fund.

10. HER WORK IS THE SUBJECT OF A BOOK, A MOVIE, AND AN OPERA.

In 1983, Fossey published the book that helped make her famous. Gorillas in the Mist is the autobiographical account of her first 13 years in the African jungle and the scientific discoveries she made about the gorillas living there. The title went on to become a bestseller. Five years later, Sigourney Weaver starred as Fossey in a film of the same name. The biopic snagged five Oscar nominations and converted Weaver into a gorilla conservationist.

There's another dramatization of Fossey's life that's not so widely known: In 2006, the Kentucky Opera VISIONS! program staged an opera called Nyiramachabelli—a nod to the researcher's nickname.

11. HER DEATH REMAINS A MYSTERY.

Next to her groundbreaking gorilla research, Fossey is perhaps best known for her mysterious and tragic murder. On December 27, 1985, she was found dead in her cabin at her Rwandan research camp. The cause of death was a machete blow to the head, but the identity of her assailant remains unknown to this day. (A Rwandan court convicted in absentia her American research assistant, Wayne McGuire, for her murder and sentenced him to death. McGuire, who fled Rwanda before the conviction, has always maintained his innocence.) Fossey was buried in the nearby mountains beside the grave of her favorite gorilla Digit, who had been slaughtered by poachers years earlier. Before she was killed, Fossey wrote one final entry in her diary. It reads:

“When you realize the value of all life, you dwell less on what is past and concentrate on the preservation of the future.”

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