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Surface and subsurface soil samples analyzed for this investigation were collected from the hyperarid Yungay region in the Atacama Desert, Chile. This report details the bacterial diversity derived from DNA and PLFA extracted directly from these extremely desiccated soils. Actinobacteria, Proteobacteria, Firmicutes and TM7 division bacteria were detected. Ninety- four percent of the 16S rRNA genes cloned from these soils belong to the Actinobacteria phylum, and the majority of these were most closely related to the genus Frankia. A 24- hour water activity (a(w)) time course showed a diurnal cycle that peaked at 0.52 in the early predawn hours, and ranged from 0.01 - 0.08 during the day. All measured water activity values were below the levels required for microbial growth or enzyme activity. Total organic carbon ( TOC) concentrations were above the limit of detection and below the limit of quantification (i.e., 200 mu g/g < TOC < 1000 mu g/g), and phospholipid fatty acid ( PLFA) concentrations ranged from 2 x 10(5) to 7 x 10(6) cell equivalents per gram of soil. Soil extracts analyzed for culturable biomass yielded mostly no growth on R2A media; the highest single extract yielded 47 colony forming units ( CFU) per gram of soil.