NEW YORK – By studying the common stomach bacterium Helicobacter pylori present in different populations, researchers have found people both stayed in Siberia during the last Ice Age and moved there following its end, as well as moved from Siberia to the Americas in one main migration event.
H. pylori infects about half the human population and has co-evolved with people. "H. pylori is humanity's oldest commensal. Our species shares an intimate relationship with this bacterium that goes back over 100,000 years, since before the human diaspora out of Africa," Yoshan Moodley, a professor at the University of Venda in South Africa, said in an email.
As H. pylori is specific to people and has greater genetic diversity than humans, Moodley added that studying the bacterium can enable researchers to piece together a higher resolution picture of evolutionary events affecting both H. pylori and humans.
In a new study that appeared in the Proceedings of the National Academy of Sciences on Monday, he and his colleagues analyzed H. pylori samples to investigate the peopling of Siberia and the Americas. Previously, scientists had found that there were two main H. pylori populations in eastern Eurasia, hpAsia2 and hpEastAsia, and one, hspIndigenousAmericas, in North America.
For the new study, the researchers analyzed H. pylori samples from more than a dozen ethnic and language groups. The samples underwent multi-locus sequence typing of seven housekeeping genes via Sanger sequencing and 40 representative H. pylori strains from around the globe, while 54 strains from Siberia and North America underwent short-read sequencing.
Genetic structure analysis revealed 10 H. pylori subpopulations, five of which were novel: hspAltai, hspUral, hspSiberia1, hspSiberia2, and hspKet.
Most Siberian samples clustered with the partially overlapping subpopulations of hspSiberia1, hspSiberia2, and hspKet, the researchers noted. Both hspSiberia1 and hspSiberia2 were found across Siberia, though at different frequencies, while hspKet was found among ethnic Kets in central Siberia.
HspIndigenousAmericas, meanwhile, was also found among northern Siberians and was most closely related to hspAltai, a strain found only in central Siberia, and together formed what the researchers called hpNorthAsia.
The researchers additionally modeled admixture patterns among the Siberian H. pylori subpopulations. Their analysis suggested that hspSiberia1 and hspSiberia2 arose through different admixture events. In particular, hspSiberia1 is likely a mix of hpAsia2 and hpNorthAsia that took place about 2,630 years ago, while hspSiberia2 is a mix of hpAsia2 and hpEastAsia that occurred about 2,933 years ago.
These genetically admixed Siberian H. pylori subpopulations indicate there was genetic contact between different H. pylori populations — and the people hosting them — following the last Ice Age, the researchers noted. It further suggested that people both stayed in Siberia during that time as well as repopulated the region from the south.
Meanwhile, modeling of the indigenous North American H. pylori populations suggested that an H. pylori population ancestral to those now found among Siberian individuals colonized North America about 12,000 years ago. However, they noted that this event occurred before the H. pylori subpopulation found in eastern Siberia evolved, suggesting that the people who now live in that region are not the people who are the most closely related to Native Americans. The indigenous North American H. pylori population additionally underwent a population bottleneck either just before or during the migration to North America before then expanding. These findings, Moodley noted, are in line with other studies of the peopling of the Americas.
Moodley added he is currently involved in efforts to collect and analyze additional H. pylori samples, such as ones from northern North America and Greenland, which could provide further details about migration events into the region, and from other key points in history. "It would also be very helpful to obtain H. pylori from other prehistorically important human crossroads, like island south-east Asia and central-southern Africa, not to mention from ancient human remains, such as pre-Columbian or Egyptian mummies," he said.