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Helicobacter Pylori Subpopulations Evolved During Colonization of Americas

NEW YORK (GenomeWeb) – Subpopulations of the stomach-dwelling Helicobacter pylori can arise fairly quickly, according to a new genomic analysis.

H. pylori colonizes the human stomach, where it can dwell for decades, and has been linked to gastric cancer, particularly in Latin American populations. An international team of researchers examined the genetic diversity of H. pylori in North American and Old World populations. As they reported in PLOS Genetics today, the New World H. pylori subpopulations largely reflected admixture of European and African strains brought over by colonists and slaves, not Native American ones.

"Helicobacter pylori has often been described as a pathogen which is mostly passed from parent to child. Our study shows that in the Americas its evolution has been much more dynamic," the University of Bath's Daniel Falush said in a statement.

He and his colleagues examined the genomes of 401 global H. pylori isolates, samples that spanned Latin America, Europe, Africa, the US or Canada, and beyond. Population structure analyses based on both chromosome painting and principal components analysis revealed 12 distinct H. pylori populations, five of which were specific to the New World. The seven Old World populations — three African, one East Asian, one Asian, and two European populations — had been reported previously, except that the European isolates could be further divided geographically into northern and southern groups.

The isolates from North America, meanwhile, included four that appeared to be European/African hybrids and one resembled a mix of East Asian and European ancestry. The researchers also noted that some North American isolates clustered within the European subpopulations and that they largely lacked admixture from Native American H. pylori strains. Additionally, isolates of European and African origin in the US remained largely distinct, while isolates in Colombia and Nicaragua were more admixed.

The New World H. pylori populations exhibited not only evidence of admixture, but also of genetic drift, the researchers reported. For instance, they noted that among the hspAfrica1NAmerica and hspAfrica1Nicaragua subpopulations, the African component was the most drifted one, indicating that these bacterial lineages likely underwent rapid demographic increase in the Americas.

The researchers also reported that local admixture occurred in the Americas. The hspEuropeS isolates found in Nicaragua, for instance had more hspAfrica1Nicaragua ancestry than hspEuropeS isolates from other regions.

At the same time, within the North American isolates, a trio of genes exhibited more Asian ancestry than would otherwise have been expected. The genes — AlpB, HofC , and FrpB4  — all encode outer membrane proteins. In particular, among Latin American isolates, certain hofC alleles were nearly fixed, suggesting that they confer a selective advantage.

To Falush and his colleagues, this suggested that H. pylori can spread and adapt quickly. "Our results on the population structure in the Americas shed new light on the relationship between human migration and H. pylori diversity," they wrote. "In particular, we show that at least during human population upheavals, evolution within geographic locations is far more dynamic than the broad correlation with human genetic variation would suggest and that novel subpopulations can arise by a combination of genetic drift and admixture within hundreds of years."