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14 THE SCIENTIST | the-scientist.com

Notebook

NEWS AND ANALYSIS

WIKIMEDIA COMMONS, CAZADORDEMOLINOS

MARCH 2019

A Lost Microbial

World

D

eep within Northern Mexico’s

Chihuahuan Desert lies the Cuatro

Ciénegas Basin, a butterfly-shape

valley where small turquoise lagoons dot the

landscape. These hidden oases possess con-

ditions remarkably similar to those of the

planet’s prehistoric past and house many

organisms, including fish, diatoms, and bac-

teria, that cannot be found anywhere else on

Earth. The aquatic system is also one of the

few places where stromatolites—rock- or

reeflike structures, built up by microbes,

that once dominated the shores of ancient

oceans—still live and grow, their surfaces

made up of active microbial colonies.

The unusual features of the Cuatro

Ciénegas Basin and its inhabitants have

drawn many scientists to the area since it

was first encountered by biologists in the

late 1930s. Valeria Souza, a microbiologist

at the National Autonomous University of

Mexico, was introduced to Cuatro Ciéne-

gas nearly two decades ago by Jim Elser,

an ecologist who was investigating stro-

matolites in the basin. “It was obvious to

me that working there wasn’t viable with-

out closer collaboration with Mexican sci-

entists,” Elser, who is now at the University

of Montana, recalls. Souza has been study-

ing the basin ever since.

Since the early days of her work in

Cuatro Ciénegas, Souza has been interested

in the microbial communities that inhabit

the basin. The nutrient composition of the

lagoons is quite different from that found

elsewhere in the world, Souza says, probably

due to the inflow of water from deep aqui-

fers under the mountain—which harbors

ancient sediments and clay—at the center of

the valley. With high levels of sulfur and very

low concentrations of phosphorus, the water

in Cuatro Ciénegas is much more similar to

oceans of the Precambrian era, which ended

approximately 542 million years ago, than to

modern-day seas. Most of Earth’s contem-

porary life forms require more phospho-

rus in the environment to survive, so Souza

and her colleagues were puzzled when they

found a high level of microbial diversity in

the area (PNAS, 103:6565–70, 2006). “This

is probably [one of ] the most diverse places

on Earth,” Souza says. “And I’ve been trying

to understand w h y.”

Given the prehistoric Earth–like con-

ditions of the basin, Souza and her col-

BLUE LAGOON: Oases scattered around the

Cuatro Ciénegas Basin in Northern Mexico are

home to ancient microbial life.