Scientists Coax Secrets From Living Soil Crusts

Biological soil crusts (BSCs), as the name might suggest, are rather unprepossessing entities, typically presenting themselves as dark, mottled patches on desert soils.

From a microbiological perspective, however, they are fascinating:  living, symbiotic communities of cyanobacteria, mosses, and algae that can survive – indeed, thrive — where most other things wither and die.

Scientists have long known that BSCs respond rapidly to surface moisture.  After a desert rain, they plump up and green up (those being relative terms for crusts) quickly – sometimes in as little as 15 minutes. But researchers didn’t have a very good handle on how BSCs do it. Until now:  A paper published in the latest issue of the Journal Nature by a team of scientists from Lawrence Berkeley National Laboratory peels back the mystery from this microbial oddity by identifying the genes involved in the response of cyanobacteria to hydration and desiccation.

“Previously, nothing was really known about the actual gene expression for (BSE) cyanobacteria,” said Lara Rajeev by phone. Rajeev, a scientist at the Physical Biosciences Division, co-wrote the article with Ulisses Nunes da Rocha, Niels Klitgord, Eric Luning, Julian Fortney, Seth Axen, Patrick Shih, Nicholas Bouskill, Benjamin Bowen, Cheryl Kerfeld, Ferran Garcia-Pichel, Eoin Brodie, Trent Northen and Aindrila Mukhopadhyay, all of Berkeley Lab.

The researchers identified the genes responsible for both bringing the cyanobacteria M. vaginatus—the dominant cyanobacteria in many BSCs—out of dormancy when water was available, and putting them back into an inert state when things started drying out.  And the scientists were also able to determine which specific genes were active at different points of the hydration cycle.

      To prepare for their research, the team constructed a “microcosm” room that mimicked a desert setting.  BSC samples were collected near Moab, Utah, transported to the microcosm room, and subjected to the equivalent of three-day rain events, followed by subsequent drying:  the kind of weather cycles you can expect in the deserts of the American Southwest.

“It’s really important in these kinds of experiments to duplicate natural settings and cycles,” said Rajeev. “Collecting the BSC samples was the easy part.  Getting the conditions right in the microcosm room was more challenging.”

—Glen Martin

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