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NewsvineI haven’t felt lonely at all this week. That’s because I recently found out that I have lots of company. The bacteria in and on my body outnumber my own cells by a factor of 10 to one.
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From birth on, human beings are crawling with bacteria. Bacteria swim in our mouths, carpet our intestines and set up shop between our toes. Some are good, some are bad and most seem not to trouble us either way.
Our bacterial passengers have made news this week as a result of a new study. Scientists were interested in the kind of bacteria that colonize human skin. While other bacteria, like the bacteria of our mouths and intestines, have been well studied, skin bacteria have long been overlooked. So, NYU researchers set out to remedy that. They swabbed the forearms of six healthy volunteers, and used genetic analysis to tell what kinds of bacteria were clinging to their skin.
The results were surprising. The scientists found 182 species of bacteria, including a dozen that had never been seen before! Each subject had about 50 species. And 75 percent of those were shared with nobody else. What’s more, when the subjects were re-examined several months later, many of the original bacteria had been replaced by new ones.
We are walking ecosystems! This is so weird, and so awesome. I can’t focus in lecture anymore, because I’m marveling at the microbial zoos all around me. What yet-to-be-discovered microbe is he hosting on his kneecap? Are two species locked in a battle for control of her earlobe? Was his shower that morning a microbial holocaust?
More than just inspiring curiosity, our unique bacterial bouquet can affect us in surprising ways. Yours could be making you fat.
Gut bacteria are the unsung heroes of digestion. They break down knotty carbohydrates, crunch sugars into manageable bits and even produce vitamin K for their human hosts. Different people have different assortments of these tiny helpers. In the name of science, researchers at Washington University School of Medicine in St. Louis recently did something very disgusting. They dug through feces from heavy and thin volunteers and analyzed its bacterial content. Interestingly, they found that feces from obese individuals held different bacteria than feces from their lean counterparts. The fat volunteers had 20 percent more bacteria from a class called Firmicutes and 90 percent fewer bacteria from a class called Bacteroidetes. Next, the same obese volunteers lost weight on a yearlong diet. Their gut flora was then analyzed again (more picking through feces!). The now-leaner volunteers had gained Bacteroidetes and lost Firmicutes.
So, losing weight can change the microbial community in our guts. But the reverse is also true. In another experiment, biologists raised mice in a sterile environment, so they would have no gut flora at all. Half of these microbe-free mice got injections of gut bacteria from fat mice, and the other half were injected with bacteria from skinny mice. The mice with the “fat” microbes gained twice as much weight as the mice with the “skinny” microbes.
How can bacteria be affecting weight gain? It turns out some bacteria do their job better than others. An individual with more efficient bacteria gains more calories from the same cheeseburger than someone with less efficient bacteria. Over time, those extra calories can add up.
Beyond making us fat or thin, bacteria can teach us about our history. Scientists generally agree that modern humans had their genesis in Africa and gradually fanned out to all the places we find them today. But it’s hard to know when this all happened. (I guess no one thought to leave a note.)
Enter bacteria to the rescue! Helicobacter pylori are stomach microbes that look like hot dogs with hair. They gained infamy as the bugs that cause ulcers, but they are actually present in most people without making them sick. Humans likely caught them from big cats (like cheetahs or lions) before our species left Africa approximately 40,000 years ago. Because they have been our passengers for so long, they can tell us about our history. Bacterial genes, like other genes, tend to accumulate mutations at a steady rate, which makes them a kind of microbial clock. If we test the Helicobacter pylori from a Maasai warrior against the Helicobacter pylori from a Wall Street day trader, we can compare their unique mutations. For example, if we find that the day trader’s bacteria has 20 mutations that are different from the warrior’s, and we know mutations occur once every thousand years, we have a date for the last common ancestor of the Maasai and the New Yorker. With lots of comparisons like that, a map of human migration starts to take shape.
Bacteria: instigators of wonder, thwarters of diets, keepers of human history. I think being covered in microscopic hangers-on is ego-inflating (I am their whole universe!) and also depressing (I’m host to a huge number of freeloaders). But like it or not, bacteria are here to stay. Now, mine are going to keep me company while I do my homework.