In the study published in Nature Communications on Nov 11, 2022, entitled Repeated out-of-Africa expansions of Helicobacter pylori driven by replacement of deleterious mutations, Prof. Daniel FALUSH’s group at the Intitut Pasteur of Shanghai, the Chinese Academy of Sciences and its collaborators showed that African Helicobacter pylori have a fitness advantage, due to not having been through the “Out-of-Africa” bottleneck that occurred when humans left Africa more than 50,000 years ago and successfully colonized the rest of the world. This advantage has allowed bacteria from Africa to spread repeatedly in the last 10,000 years, outcompeting the resident strains and generating hybrid bacteria.
Helicobacter pylori is a human pathogen living in the human stomach that is responsible of most cases of gastric cancer, MALT lymphoma and gastroduodenal ulcer disease. It is often transmitted from stomach to stomach within the same household and consequently its population structure is similar to its human host. However European H. pylori populations from both north and South Europe trace a large fraction of their ancestry to recent migrations from Africa. People from Spain and Portugal and Greece do have a few percent recent African ancestry but there is no corresponding signal in Northern Europe, implying that the demographic signal differs between humans and bacteria.
In this article, using a collection of Afro-Eurasian strains, the researchers show that this African ancestry is due to at least three distinct migration events. They also show that strains from East Asia, which have preserved the original “out-of-Africa” signal have accumulated more non-synonymous mutations than African strains, for similar levels of genetic diversity, demonstrating a big effect of the original migration out of Africa on the fitness of the bacteria. European strains, which are hybrids, have a deficit of Asian ancestry at these sites, showing that these mutations have been replaced by subsequent admixture.
The results are important because they show that although H. pylori relies on humans to spread, its DNA can spread in a different way to human DNA. They also show the importance of the out-of-Africa for bacterial fitness and for subsequent demographic events.
Ancestry of hpEuropes isolates (Image by IPS).
Painting profiles of hpEurope isolates and their putative ancestral populations from Africa and Asia showing proportion of each genome (horizontal bar) painted by each of five ancestral donor populations (circles). hpEurope isolates are grouped by country of isolation, with bars to the right indicating the H. pylori population each strain is assigned to. The representative isolates from each donor population are grouped by population, with countries of isolation listed for each group.
Contact
Daniel Falush
E-mail: daniel.falush@ips.ac.cn
