Researchers obtain genome of Helicobacter pylori from 5,000-year-old stomach contents
The stomach bacterium Helicobacter pylori is found in roughly half of the world’s present-day population, although it causes symptoms in only around 10 to 15 percent of cases. The bacterium’s association with humans is very ancient, possibly originating in East Africa 58,000 years ago. Since then, various strains have emerged as humans dispersed around the world. Thus differing strains reflect differing geographical origins and are informative about past human migrations.
The European strain hpEurope is believed to have resulted from hybridization between two ancestral strains known as AE1 and AE2. It is thought that AE1 emerged in Central Asia and later evolved into the present-day strain hpAsia2. AE2 is thought to have arisen in Northeast Africa. The two strains have been thought to have hybridized in Southwest Asia 50,000 years ago, with the recombined strain arriving in Europe when populations expanded after the Last Glacial Maximum.
To test this model, researchers obtained a genome of the bacterium from the stomach contents of ‘Ötzi’, the frozen 5,000 year old corpse that was found in 1991 in the Ötztal Alps on the border between Austria and Italy. Despite the age of Ötzi’s remains, it was thought that any H. pylori present would be similar to the present-day hpEurope strain.
Instead, it turned out that Ötzi was carrying a strain that most closely resembled hpAsia2, which is rare in modern Europeans. This suggests that the hybridisation with the African H. pylori strain actually occurred more recently than 5,000 years ago, in turn implying that there was a Chalcolithic migration from Africa. The study presents interesting evidence that the history of human settlement of Europe during this period is more complex than previously believed.
Maixner, F., Krause-Kyora, B., Turaev, D., Herbig, A. & Hoopmann, M., The 5300-year-old Helicobacter pylori genome of the Iceman. Science351 (6269), 162-165 (2016).