by Roberto
Fig. 1. A pool at Cuatro Ciénagas. By Roberto Armorcida. Source
Just a few weeks ago, we posted this Talmudic Question by Memo Berkmen: "Can you imagine a place where conditions have remained relatively constant throughout much of Earth's history, a place where microbes evolved very slowly over 3 billion years such that if we compared the sequences of modern inhabitants to their 3-billion-year-old ancestors, we would see very few changes in their genomes or metabolisms?" In response Jorge Rocha, another long-time friend of STC (and former Kolter Lab post-doc), suggested a possible place: Cuatro Ciénagas Basin, an oasis located in the central part of the Chihuahan desert (Coahuila, Mexico). Indeed, all evidence points to Cuatro Ciénagas as a place where conditions have remained relatively constant, not quite for billions of years but likely hundreds of millions of years. And most exciting for microbiologists, the microbial communities that inhabit Cuatro Ciénagas have been the subject of intense investigation for several decades, thanks to the efforts of Valeria Souza and Luis Eguiarte and their colleagues.
Jorge's bringing up the topic reminded me of a paper from 2018 by Souza, Eguiarte and colleagues which described the microbiota of Cuatro Ciénagas. What makes this location unique is that its phosphorus content has been extremely low for a very very long time. The authors suggest that this chemical feature of extreme nutrient unbalance has created a real life "lost world," into which microbial migrations have been very rare. For example, they estimate that some of the endemic clades of Bacillus arrived there in only a couple of migrations, the earliest one more than half a billion years ago. Yet, despite the relative constancy of the environmental conditions and few migrations, the microbial diversity found at Cuatro Ciénagas is astounding. From the genus Bacillus alone, the investigators discovered many new species, increasing the total know number by more than 20%. So, despite conditions being relatively constant, diversity flourished at this locality! Sadly, the entire Cuatro Ciénagas ecosystem is being rapidly drained of its water due to increases in local agriculture. Yet, not all hope is lost as there is a civil initiative Cuatro Ciénagas 2040 aiming to stop the rapid ecological degradation of this lost world.
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