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Defrosting a mummy reveals a lot about germs — and human history
(EURAC/Marion Lafogler)
Bacteria found in the gut of a 5,300-year-old mummy may help scientists understand how our germs evolved with us.
By sequencing the DNA of stomach contents found inside the "Iceman," researchers found a pretty famous type of bacteria, H. pylori — the same type of bacteria that sometimes causes ulcers in humans today. And that finding, published today in Science,
doesn't just hint that the Iceman may have been sick at the time of his
murder. As it turns out, mummy bacteria also reveals a lot about
ancient human history.Scientists only recently noticed the mummy contained a full stomach
The Iceman was discovered in 1991 by a German couple vacationing in the Italian Alps. His body had been exhumed by glacier melting close to the Austrian border. In the years after the body's discovery, scientists figured out that the Iceman lived during the Copper Age, grew up in the Alps, and that he was somewhere between 40 and 50 years old when he died. They also discovered that he died when an arrowhead lodged itself in his left shoulder, severing a major artery. In 2012, an analysis of the Iceman's DNA revealed that the Iceman had brown eyes, brown hair, Type O blood, and that he was lactose intolerant. Now, scientists have turned their attention to the organisms that lived inside the Iceman's stomach. But getting to this point in their research wasn't easy; scientists only noticed that the mummy contained a full stomach in 2010, after re-examining CT scans of the body. And even then, scientists still had to do something drastic: defrost a 5,300-year-old corpse completely to find out what might lay inside.
First, scientists had to completely defrost the mummy. Then they went into the guts through a pre-existing cut in the lower abdomen, says Albert Zink, head of the Institute for Mummies and the Iceman at the European Academy in Bolzano, Italy, told reporters yesterday. "Through the opening in the mummy, we were able to get samples of the stomach content and different parts of the stomach and intestines."
They went into the guts through a pre-existing cut
By analyzing DNA contained in the samples, scientists figured out that the H. pylori strain found in the Iceman's gut wasn't the product of a modern contamination. "The Helicobacter sequences display damage patterns, so they were clearly of ancient origin," says Frank Maixner, coordinator at the Institute for Mummies and the Iceman. The researchers also determined that the Iceman carried a strain that's associated with inflammation in modern-day humans. In addition, the researchers found signs his immune system had been fighting off the infection. That might mean the Iceman was sick when he died, but his stomach lining wasn’t preserved well enough for researchers to know for sure.
Finding out if the Iceman felt sick before his death wasn't the researchers' main goal, however. What they wanted to do was use H. pylori's genome to uncover new information about human history.
That's possible because this particular bacterium only exists in human stomachs; it's transmitted when children play together, as well as from parent to child. It also happens to mutates very quickly, which means that H. pylori's DNA can give researchers an even higher resolution picture of how human populations have moved around the globe than human DNA would allow right now, says Yoshan Moodley, an evolutionary biologist at the University of Venda in South Africa and one of the co-authors of the study. In addition, scientists already know that the modern-day European population of this bacterium is made up of a roughly 50-50 combination of Asian and Northeast African bacterial populations. But what they don't know is when that mixture — one that would require close contact among disparate groups of people — took place.
That's why today's study is valuable for evolutionary biologists. The analysis of the bacteria's DNA shows it’s closely related to ancient North Indian H. pylori strains — and shares only a small amount of ancestry with North African strains. That's surprising, the researchers say, because modern European strains are closely related to North African strains. That means that the genetic mixture of ancestral bacterial strains found in modern Europeans hadn't occurred, or had not fully occurred, in Central Europe by the time of the Iceman's death.
"He carried an unmixed strain."
"Until now it was believe that this mixed strain was already present in the Neolithic [Period] — that the farmers brought this already mixed strain to Europe — and now we see in the Iceman that it wasn't like that. He carried an unmixed strain," Maixner said in a video interview. The bacteria inside the Iceman's gut was probably Paleolithic bacteria that existed in Europe at the time, Moodley said. And the African components that scientists see in modern European strains may have been "brought in by Neolithic farmers at some stage in the last 5,000 years."
It’s unlikely that today’s European mixture is the result of people from Asia walking to Europe and meeting African people there, Moodley says. Instead, the African components of modern H. pylori probably were transferred to the Middle East before moving into Europe over the last 5,000 years. The Asian bacterial population was probably widespread in prehistoric Europe; it would have evolved in the Middle East as well before spreading throughout Paleolithic Europe and Asia.
Krithi Sankaranarayanan, a microbiologist at the University of Oklahoma, says the study was well designed — but that's not all that he's excited about. He thinks the researchers' methods could be used to screen other mummies from similar or older time periods. And that's something that the researchers say they've thought of too. They're already in talks with scientists who have access to mummies in Asia, northern Europe, and South America, Zink said (mummies in Egypt had their stomachs removed, so they're pretty much off the table). And that’s promising for scientists, since it’s hard to draw population-wide conclusions based on just one specimen.
This probably isn't the last time you'll hear about the Iceman. His body is currently housed in the South Tyrolean Museum of Archaeology in Bolzano, Italy, and the researchers say that they still have sample materials left to look at, and some data to crunch. In addition, the researchers say that the Iceman didn't suffer too much from being defrosted and then re-frozen. Taking the samples didn't cause the Iceman's body any harm, Moodley said — "except maybe that he lacks some of his stomach content now."
Itchy Eyes? Sneezing? Maybe Blame That Allergy On Neanderthals
Neanderthals, represented here by a museum's reconstruction, had been living in Eurasia for 200,000 years when Homo sapiens first passed through, and the communities intermingled. The same genes that today play a role in allergies very likely fostered a quick response to local bacteria, viruses and other pathogens, scientists say.
"So I suppose that some of us can blame Neanderthals for our susceptibility to common allergies, like hay fever," says Janet Kelso of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who led one of the teams.
Scientists once thought of Neanderthals as brutish creatures who had little in common with modern humans. But as more evidence turned up, researchers realized Neanderthals were more sophisticated than previously thought and sometimes mated with early Homo sapiens.
"When modern humans were coming out of Africa, they met the Neanderthals who were living at that time in Europe and western Asia, interbred with them and carried with them some of the Neanderthal DNA as they migrated out into wider parts of the continent," Kelso says.
So Kelso and her colleagues and a second team from the Pasteur Institute decided to search through human DNA collected by the 1,000 Genomes Project for genes from Neanderthals and a third kind of early human — the Denisovans — that may be involved in regulating immunity.
Both teams identified three genes from these two extinct groups that play a role today in controlling a part of the human immune system known as "innate immunity."
"When the body detects that there is some foreign substance in the body, these are the guys that react immediately," Kelso says. "It kind of calls in the big guns" by mobilizing key immune system cells to attack.
They report the findings in two papers in the American Journal of Human Genetics.
These genes would have helped enable early humans to survive new diseases encountered as they traveled throughout the world, Kelso says.
"It's not surprising, right?" Kelso says. "Neanderthals were living in Europe and western Asia for 200,000 years before modern humans arrived on the scene. And that means that they'd had time to adapt to the local environment," including pathogens.
And when humans arrived and bred with the Neanderthals, it makes sense that evolutionary pressures would make it more likely that these ancestors of modern humans retained genes that allowed them to "adapt quickly and rapidly to local pathogens," Kelso says.
But there appears to be a downside for people who still carry these particular genes today. The same bits of DNA make the immune system more likely to overreact to certain stimuli such as pollen and animal hair, and increase the risk of developing other sorts of allergies.
"This is a trade-off of sorts," Kelso says. It remains unclear whether those genes also are still protecting people from pathogens, she and other scientists say.
"That's sort of the $1 million question," says Lluis Qutintana-Murci, with the Pasteur Institute in Paris, who led the second research team. "What was good in the past may or may not be good for us today."
But it is clear that Neanderthal genes do more than just affect the immune system. Previous research found Neanderthal DNA seems to influence human hair and skin, for example.
"I think this is really just the tip of the iceberg about how mating with Neanderthals influences all sorts of traits today," says Josh Akey, a professor of genome sciences at the University of Washington who studies Neanderthal and human DNA.
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