N-188. The Effect of Moisture on Soil Microbial Communities in the Mojave Desert

E. P. Bryant1, S. Rech1, C. P. McKay2;
1San Jose State Univ., San Jose, CA, 2NASA Ames Res. Ctr., Mountain View, CA.

The Mojave Desert -Death Valley region of Southern California represents the driest area of North America, with a precipitation range from 23 cm in the Tehachapi Mountains to a minimum of 6 cm per year in Death Valley. This precipitation gradient offers an excellent opportunity for investigating the soil microbial communities inhabiting this extremely dry region. We began this study during the NASA Spaceward Bound: Mojave program in March 2007. Seven sampling sites along a 200 km west-east transect were selected. A 10 x 10 m square was established with minimal plant coverage and six samples were taken from the top 7-8 cm of soil. Viable counts on ½ strength R2A agar indicated a decrease in microbial numbers corresponding to a decrease in annual precipitation: 3.3x106 CFUs/gm to 2.66x104 CFUs/gm. Phylogenetic analysis resulting from cloning of the 1.5kb 16S rRNA gene is in progress. Four of the seven samples have provided fourteen possible clones, and transformation of the remaining samples and further cloning is ongoing. Community analysis is performed using Denaturing Gradient Gel Electrophoresis. PCR products of ~183 bp for DGGE analysis have been obtained. DGGE processing should result in banding patterns that will allow a visual comparison of the microbial communities at all sites. This data, plus the phylogenetic analysis should present a consistent means for evaluating the relationship between the microbial communities and precipitation.