Thursday, January 14, 2016

The Testimony Of The Gut Bacteria

The stomach bacterium Helicobacter pylori is one of the most prevalent human pathogens. It has dispersed globally with its human host, resulting in a distinct phylogeographic pattern that can be used to reconstruct both recent and ancient human migrations. 
The extant European population of H. pylori is known to be a hybrid between Asian and African bacteria, but there exist different hypotheses about when and where the hybridization took place, reflecting the complex demographic history of Europeans. 
Here, we present a 5300-year-old H. pylori genome from a European Copper Age glacier mummy. The “Iceman” H. pylori 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.
Frank Maixner, Ben Krause-Kyora, Dmitrij Turaev, Alexander Herbig, et al., "The 5300-year-old Helicobacter pylori genome of the Iceman" 351-6269 Science 162-165 (January 8, 2016).

This is a counterintuitive result.  There was a major population shift in Europe shortly after the Ice Man died ca. 3300 BCE.  But, the migration that changed it all arrived from Asia, not Africa.

It would be great to see if the African version of H. pylori was present in steppe populations, or in Western Europeans, before the Copper Age/Early Bronze Age demographic shift in Europe that gave rise to its modern population genetics.

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