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In the Atacama desert in northern Chile, one of the driest places on Earth, microorganisms can make a living by drawing water from the rocks they colonize.
Through field work and laboratory experiments, researchers at the University of California, Irvine, as well as Johns Hopkins University and UC Riverside, gained a deep understanding of the mechanisms by which some cyanobacteria survive in hostile environments.
The new ideas, published in procedures of the National Academy of SciencesDemonstrate how life can flourish in places without much water, like Mars, and how people living in arid regions can one day get hydration from available minerals.
“The Army Research Office funded this project because they want to understand how organisms can survive in extreme environments,” said lead author David Kisailus, a professor of materials science and engineering at UCI. “They also wanted us to help translate that so that humans can cope with the harshest conditions, either in the middle of the desert or while exploring other planets.”
The research team focused on the interactions of Chroococcidiopsis, a desiccation-resistant cyanobacterium found in deserts around the world, and gypsum, a calcium sulfate-based mineral that contains water. Colonizing life forms exist under a thin layer of rock that provides a measure of protection against Atacama’s high solar irradiance, extreme dryness and strong winds.
Co-author Jocelyne DiRuggiero, an associate professor in the Johns Hopkins University Department of Biology, traveled to the remote desert to collect gypsum samples, which were brought to her laboratory in the United States. He cut small pieces that contained cyanobacteria and sent them to Kisailus’ laboratory for Material Analysis.
In one of the study’s most surprising discoveries, researchers discovered that microorganisms change the very nature of the rock they occupy. By extracting water, they cause a phase transformation of the material, from gypsum to anhydrite, a dehydrated mineral.
According to DiRuggiero, the impetus for the published work came when Wei Huang, a UCI postdoctoral researcher in materials science and engineering, detected data showing an overlap in the concentrations of anhydrite and cyanobacteria in the gypsum samples collected in Atacama.
“Our analysis of the rock regions where the microbes colonized revealed a dehydrated phase of calcium sulfate, suggesting that they extract water from the rock to survive,” said Kisailus. “We wanted to do some more controlled experiments to validate that hypothesis.”
DiRuggiero’s team allowed the organisms to colonize half-millimeter cubes of rock, called coupons, in two different conditions: one in the presence of water, to mimic a high humidity environment, and the other completely dry. In the middle of the humidity, the plaster did not transform to the anhydrite phase.
The cyanobacteria “didn’t need water from the rock; they got it from their environment,” Kisailus said. “But when placed under stress conditions, the microbes had no alternative but to extract water from the gypsum, inducing this phase transformation in the material. “
His team used a combination of advanced microscopy and spectroscopy to examine interactions between biological and geological counterparts, and found that organisms pierce rock like small miners by excreting a biofilm containing organic acids.
Huang employed a modified electron microscope equipped with a Raman spectrometer to discover that cyanobacteria used acid to penetrate gypsum in specific crystallographic directions, only along certain planes where they could more easily access the water between the calcium ion faces. and sulfate.
Kisailus said the project was a great example of interdisciplinary collaboration between microbiologists and materials scientists.
“Researchers have long suspected that microorganisms could extract water from minerals, but this is the first demonstration of this,” DiRuggiero said. “This is an amazing survival strategy for microorganisms living on the dry edge of life, and it will guide our search for life elsewhere.”
Robert Kokoska, Ph.D., program manager at the Army Research Office, an element of the Army Research Laboratory of the United States Army Combat Capability Development Command, noted: “The Army has a great interest in how well-adapted micro-organisms in extreme environments can be exploited for novel applications such as materials synthesis and power generation in these hostile environments This study provides valuable clues to discover the evolved design strategies used by these living native microbes in the desert to maintain its viability in the face of multiple environmental challenges. “
Reference
Huang et al. (2020). Mechanism of extraction of water from gypsum rock by desert colonizing microorganisms. PNAS. DOI: https://doi.org/10.1073/pnas.2001613117
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