The Iceman’s Gut Microbes Cometh
Analysis of microbes from the gut of the Iceman—a 5300-year-old Copper Age European glacial mummy—provides insights into not only his health status right before he was murdered, but migration patterns of humans and their microbiota.
Helicobacter pylori, one of the most prevalent human pathogens, is globally dispersed but has a distinct phylo-geographic pattern that can be used to reconstruct recent and ancient human migrations. The pathogen accompanied modern humans out of Africa and has associated with us for at least 100,000 years.
The current European population of H pylori is a hybrid between Asian and African bacteria. However, there are different hypotheses about when and where the hybridization took place.
Frank Maixner et al analyzed the H pylori genome from the Iceman.
In the 7 January issue of Science, they report that the Iceman H pylori (the hpAsia2 strain) is a nearly pure representative of the bacterial population of Asian origin that existed in Europe before hybridization, suggesting that the African population arrived in Europe within the past few thousand years.
To obtain the H pylori for analysis, Maixner et al screened 12 biopsy samples from the gastrointestinal tract of the Iceman. Stable isotope analyses showed that the Iceman originated and lived in Southern Europe, in the Eastern Italian Alps. Genetically, he most closely resembles early European farmers.
The Iceman’s stomach was discovered in a reappraisal of radiological data and contains the food he ingested shortly before his death. The study material included stomach content, mucosa tissue, and content of the small and large intestines. Using direct PCR, metagenomics diagnostics, and targeted genome capture, the authors determined the presence of H pylori and reconstructed its complete genome.
Maixner et al state that detection of an hpAsia2 strain in the Iceman’s stomach was surprising because despite intensive investigation, only 3 strains of hpAsia2 have ever been detected in modern Europeans.
A press release from Science explained that modern strains in Europe share much higher ancestry with North African strains, indicating the influence of recent migrations that must have occurred after the Copper Age.
A news story in Science wrote that the study is significant because it suggests that bacteria like H pylori can evolve and adapt to new populations much more rapidly than expected. Christina Warinner (University of Oklahoma, Norman) told Science “A surprising result of this and other recent ancient DNA studies is that many genetic traits and microbial strains that were once thought to be very ancient are actually quite recent.”
Daniel Falush (Swansea University, United Kingdom) told Science “this shows there was an African lineage (of H pylori) that had a very big transmission advantage—it spread right across Europe faster than we expected.” It is not clear why it spread so rapidly—perhaps it thrived on a dietary change, the spread of agriculture in which people settle in closer quarters than hunter-gatherers, or poorer hygiene, he said.
Martin Blaser (New York University) explained to NPR health blog that the H pylori bacterium has been helping and hindering humans since way before the iceman.
Mark Achtman (University of Warwick, UK), told the New York Times that the authors of the Ötzi paper had done well to extract the ulcer bacterium from the iceman, but that it was difficult to infer from a single sample anything about the bacterium’s distribution in Europe 5000 years ago.
Maixner et al also found that the strain of H pylori analyzed was producing virulence factors, indicating that the Iceman may have been feeling ill on the day he was murdered. It appears that he had harbored the H pylori long enough to have a gut reaction to the microbe—his tissues expressed 22 proteins associated with inflammation. He may have had gastritis or an ulcer, but his stomach was completely full of the meat of an alpine ibex when he died. “He ate quite a lot!” Maixner told Science.
The mummy, named Ötzi, was discovered at the mountain border between Austria and Italy in 1991. In extensive examinations, scientists had previously found that the 40-something farmer had worn joints, hardened arteries, gallstones, and a nasty growth on his little toe (perhaps caused by frostbite). Despite all this, and a fresh arrow wound to his shoulder, it was a sudden blow to the head that proved fatal to Ötzi.