Friday, November 15, 2024

Quickie Hypothesis

Stefan Milo put out this video about the Black Death today.   He got me thinking,

New genetic research shows the Yersinia pestis bacteria appeared many different times on the Eurasian steppes and then swept west over Europe.  These strains were unique and seemed to be spontaneous.

These are some of the questions raised by the research:

What was the reservoir for Y pestis.   It lives in fleas now, but not then.   They can’t find an animal reservoir.

Why were there so many different strains that didn’t survive?

Why was it suddenly so much more virulent?


You can probably guess my answer.

There was no animal reservoir.  Yersinia pestis evolved from Y. pseudotuberculosis.  Y. pseudotuberculosis lives in the soil and on vegetables.  Occasionally, as humans would forage through the landscape they would disturb the soil or eat infected food.  It causes intestinal infections in  humans, but they are usually mild.

However, the Yersinia family of bacteria have a number of interchangable genetic sequences.   Plasmids and DNA fragments inherited from other species.  They recombine often to create strains with varying virulence.   I assume that this accounts for the sporadic isolated outbreaks.

The virulence factor for Yrsinia bacteria reside on one kind of fragment. It codes for a group of  iron extracting molecules.   The more iron it gets, the more deadly it is….

See where we’re going?

Porphyromonas gingivalis gjngipains are molecules that extract iron from the blood.   They float around until they find some hemoglobin, and they combine with it and release the iron.

A virulent strain of Y. pseudotuberculosis would clearly thrive in a host infected by PG.  And I bet over time it mutated to live in the blood rather than the intestines.  This is what took it to the next level.

There were already well established long range trade routes.   Of course it worked it way back to the steppes.   And then they started farming too. 


Oops, forgot the citations...

Yersinia pestis, the cause of plague, is a recently emerged clone of Yersinia pseudotuberculosis

https://www.pnas.org/doi/abs/10.1073/pnas.96.24.14043

Yersinia pseudotuberculosis IP32953 survives and replicates in trophozoites and persists in cysts of Acanthamoeba castellanii

https://pmc.ncbi.nlm.nih.gov/articles/PMC4661780/

 The Yersiniabactin Transport System Is Critical for the Pathogenesis of Bubonic and Pneumonic Plague

https://pmc.ncbi.nlm.nih.gov/articles/PMC2863531/

Hunger for iron: the alternative siderophore iron scavenging systems in highly virulent Yersinia

https://pmc.ncbi.nlm.nih.gov/articles/PMC3510459/