Seasonal and spatial variability in total and active bacterial communities from desert soil

Studies describing the diversity of microorganisms in drylands are based mainly on the total (DNA), and seldom on the metabolically active (RNA) portion of the bacterial communities. We predicted that in desert environments, the majority of bacteria would display low activity during the hot and dry season, resulting in comparable diversity of the total and active communities. But during the wet periods, when rain activates certain bacterial groups, the total and active communities would differ. To test our predictions, the rDNA and rRNA extracted from desert soil, were analysed in samples collected during the dry and wet seasons from three patches: under the canopy of the dominant shrub, near ant nests and in open patches. The results disproved our predictions because the RNA- and DNA-based communities significantly differed in the dry season but matched very well in the wet season samples. Further comparative analysis of the rRNA/rDNA ratio revealed the composition and structure of metabolically active members within the patches' communities. Our results suggest that in desert environments, the activity of soil bacterial communities is not restricted by water availability or patch types and could be fully described only, by concomitant analysis of the total and active members.