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Ancient H. pylori offers insight into history of early bacteria, European settlers
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Researchers have determined Helicobacter pylori sequences reconstructed from a 5,300-year-old European mummy to be of a primarily Asian origin, suggesting that the Asian-African hybrid strain of the bacterium currently seen among Europeans may have developed later than previously believed.
“Predominant intrafamilial transmission of H. pylori and the long-term association with humans has resulted in a phylogeographic distribution pattern of H. pylori that is shared with its host,” Frank Maixner, PhD, microbiologist with the European Academy, and colleagues wrote. “This observation suggests that the pathogen not only accompanied modern humans out of Africa, but that it has also been associated with its host for at least 100,000 years. Thus, the bacterium has been used as a marker for tracing complex demographic events in human prehistory.”
Figure 1. A reconstructed image of the Iceman.
Source: Reconstruction by Kennis © South Tyrol Museum of Archaeology, Foto Ochsenreiter
The mummified remains of the “Iceman” were recovered from a glacier in 1991, according to a press release, and have since been examined by researchers for insights into the biology and lifestyles of Copper Age Southern European settlers. In this most recent effort, Maixner and colleagues screened 12 biopsy samples from the Iceman’s gastrointestinal tract for H. pylori. Following PCR, metagenomics diagnostics and targeted genome capture of the samples — which comprised mucosa tissue as well as stomach, small intestine and large intestine content — the researchers were able to detect H. pylori and reconstruct its complete genome.
Metagenomic analysis yielded a distribution of H. pylori DNA reads similar to those found among modern humans with the infection, they wrote. There were slightly fewer genomic variants among the Iceman’s H. pylori DNA than what is often observed in contemporary strains. Stomach proteins suggested evidence of an inflammatory host response; however, due to decomposition of the stomach mucosa, it was uncertain whether the Iceman experienced clinical complications resulting from the infection.
A comparison of the reconstructed pathogen to a database of 1,603 H. pylori strains assigned the Iceman’s bacterium to a modern strain often found in Central and Southern Asia. Maixner and colleagues wrote that this finding was surprising, as Europeans are predominantly colonized by recombinant strains containing a proportion of an ancestral African strain greater than what was seen in the Iceman. Furthermore, it suggests that exposure to the African strain during the Copper Age was low, and that European exposure to this strain must have happened much later than previously proposed.
“We were able to tease out the individual Helicobacter sequences and reconstruct a 5,300-year-old [H. pylori] genome,” Maixner said in a press release. “The recombination of the two types of Helicobacter may have only occurred at some point after Ötzi’s [the Iceman’s] era, and this shows that the history of settlements in Europe is much more complex than previously assumed.” – by Dave Muoio
Disclosure: The researchers report no relevant financial disclosures.
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