Miraculous things happen to the desert when it rains everything changes from brown to green and organisms that have not been seen for months make a brief .emergence from underground lairs.

In fact, even the deserts soil turns visibly green following the rare desert rain, as hidden filaments of photosynthesizing cyanobacteria suddenly hydrate. Lying a few millimeters deep, these primitive prokaryotes quickly glide upward, migrating en mass to the surface for an hour or so of light exposure until the dirt begins to dry. Then, just as suddenly, they return again to the subsurface, where they begin the long wait for the next rain.

The existence of such cryptic communities of microbes has long been known, and it has long been assumed that the organisms behavior can be explained by common light-responsive behavior. Now, a new finding by Arizona State University microbial ecologist Ferran Garcia-Pichel and Olivier Pringault of the Biological Oceanography Laboratory at the University of Bordeaux shows that phenomenon is actually more complicated, with significant implications for the behavior and ecology of other underground microbes. The research is reported in the September 27 issue of the journal Nature.

Observing several different species of soil crust-inhabiting cynobacteria, the team found that the bacterias movements were affected by the presence or absence of water, not just light the first time such behavior has ever been observed in bacteria.

According to Garcia-Pichel, the team was first intrigued by a serendipitous field observation. What we discovered was that when one of these wetting events took place, the cyanobacteria came up to the surface of the soil. But once the soil started drying out, the cyanobacteria returned to the subsurface though the light didnt change. Essentially nothing changed except the availability of water, he said.

Subsequently, the bacteria were moved to a laboratory setting and were tested under
'"/>

Contact: James Hathaway
Hathaway@asu.edu
480-965-6375
Arizona State University
26-Sep-2001