Long Live the Salt of the Earth

Psychedelic microbes. Rock crystals from Mexico host a colorful variety of bacteria.

SALT LAKE CITY--It's as odd as finding your couch-potato cousin skiing a steep slope. Researchers studying salt crystals from Mexico have stumbled on a diverse community of microbes normally found in more hospitable surroundings--like dirt, for instance. The findings suggest that the diversity of bacteria in extreme environments is even greater than previously thought, and the authors suggest that salt deposits on other planets might be a good place to search for extraterrestrial life.

Astrobiologists look to extreme environments on Earth for hints about places that might harbor life on other planets. Salt crystals, similar to those found on Mars, might be one such place. Microbiologist John Spear of the University of Colorado, Boulder, and colleagues investigated pound-size chunks of crystallized salt from salt production facilities in Baja California. Inside the rocks, technicolored microbes that range from yellow-green to pinkish purple hide out.

Spear expected to find species of archaebacteria, the oldest living organisms on Earth, because they're known to thrive in such extreme conditions. But when his team compared DNA sequences from the bacteria in the rock samples with those available in databases, he discovered an entire microbial ecosystem consisting of a wide variety of both archaebacteria and eubacteria, common "modern" bacteria that normally take up residence in lush places such as cheese and humans. Many had never been seen before. Of the 150 eubacteria species found, nearly a third had not previously been catalogued, likewise for two-thirds of the 90 archaebacteria species in the samples. He found many varieties of eubacteria species, including some that usually prefer soil or ocean living--all living inside rock salt. "So much diversity," he muses. He presented the findings here 21 May at the general meeting of the American Society for Microbiology.

The community may not be as diverse as Spear thinks, cautions microbiologist Russell Vreeland from West Chester University, Pennsylvania, who hunts for microbes trapped in ancient salt crystals. He notes that sequencing DNA without cultivating the organisms might overestimate the number of unique species. But he says it makes sense that bacteria can eke out a living inside the salt. Growing salt crystals offer wet crevices to keep them from drying out, Vreeland says. "The crystals could protect the organisms for many years--they could even protect them in space," he says, suggesting astrobiologists might want to get their hands on some salt rocks from Mars.

Related sites
Astrobiology at the University of Colorado
Spear's department at the University of Colorado, Boulder