Contributed by Thomas Partin and Austin Piccolo

Species do not live in a world separate from each other. Organisms interact with other organisms everyday, and over time adapt to each other accordingly. Often, the evolution of two species can become strongly linked to each other, for better or worse. Heliobacter pylori is a bacteria that thrives in the acidic conditions of the human stomach. It causes stomach ulcers and is strongly correlated with gastric cancer. As recently as the 1980’s, the idea of a bacteria being able to survive in the stomach’s harsh conditions and being responsible for this disease was so controversial that it took one doctor intentionally infecting himself to prove its role in stomach ulcers. That doctor later won the Nobel prize in medicine for his work.

H. pylori did not first start infecting humans in the 80’s though. H. pylori and humans have been living (and battling) together for millennia. The earliest humans also played host to H. pylori. One way this can be shown is a creative use of a phylogenetic tree. Scientists sampled many different strains of H. pylori, and used them to create an ancestral tree of the different strains. They then compared the tree they made to geographic locations of their samples. What they found was that lineages of H. pylori matched perfectly with the migration patterns of ancient humans as they moved out of Africa. Newer strains of H. pylori are found where humans migrated to most recently. The strains were carried and dispersed based on how early humans moved around the globe.

This intimate relation between H. pylori and humans provides a great opportunity to explore coevolution. Humans and H. pylori have been locked in an arms race for thousands of years. H. pylori colonization poses serious health consequences to the host, which creates a selective pressure for humans that can prevent H. pylori infection. Likewise, the human body is an incredibly hostile environment towards foreign invaders like H. pylori, which creates a strong selective environment for H. pylori cells that can overcome human defenses. There is evidence this selective pressure is so strong that H. pylori begins adapting specifically to the host after initial colonization. Although not an innate aspect of human biology, antibiotics are another human defense against H. pylori. Antibiotic use creates a selective pressure for H. pylori that is so strong that resistant strains can develop remarkably quickly after attempted treatment.

Please watch the below video to learn more!

https://www.youtube.com/watch?v=01NY55VV0Rg;feature=youtu.be

For further information see:

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Gao, W., Cheng, H., Hu, F., Li, J., Wang, L., Yang, G., Xu, L., Zheng, X. 2010. The Evolution of Helicobacter pylori Antibiotics Resistance Over 10 Years in Beijing, China. Helicobacter. 15: 460-466.

Oh, J.D., Kling-Bäckhed, H., Giannakis, M., Xu, J., Fulton, R.S., Fulton, L.A., Cordum, H.S., Wang, C., Elliott, Glendoria., Edwards, J., Mardis, E.R., Engstrand, L.G., Gordon, J.I. 2006. The complete genome sequence of a chronic atrophic gastritis Helicobacter pylori strain: Evolution during disease progression. PNAS. 103: 9999-10004.

Blecker, U., Landers, S., Keppens, E., Vandenplas, Y. 1994. Evolution of Helicobacter pylori Positivity in Infants Born From Positive Mothers. Journal of Pediatric Gastroenterology and Nutrition. 19: 87-90

Kennemann, L., Didelot, X., Aebischer, T., Khun, S., Drescher, B., Droge, M., Reinhardt, R., Correa, P., Meyer, T.F., Josenhan, C., Falush, D., Suerbaum S. 2011. Helicobacter pylori genome evolution during human infection. PNAS. 108: 5033-5038.

Marshall, B.J., Warren, J.R. 1984. Unidentified curved bacilli in the stomach of patients with gastritis and peptic ulcers. The Lancet. 323: 1311-131.

Avasthi, T.S., Devi, S.H., Taylor, T.D., Kumar, N., Baddam, R., Kondo, S., Suzuki, Y., Lamouliatte, H., Mégraud, F., Ahmed, N. 2011. Genomes of Two Chronological Isolates (Helicobacter pylori 2017 and 2018) of the West African Helicobacter pylori Strain 908 Obtained from a Single Patient. Journal of Bacteriology. 193: 3385-3386.