Abstract:
Hot desert surface soils are characterized by extremely low water activities for large
parts of any annual cycle. It is widely assumed that microbial processes in such soils are
very limited. Here we present the first metatranscriptomic survey of microbial community
function in a low water activity hyperarid desert soil. Sequencing of total mRNA revealed
a diverse and active community, dominated by Actinobacteria. Metatranscriptomic
analysis of samples taken at different times over 3 days indicated that functional
diel variations were limited at the whole community level, and mostly affected the
eukaryotic subpopulation which was induced during the cooler night hours. High levels
of transcription of chemoautotrophic carbon fixation genes contrasted with limited
expression of photosynthetic genes, indicating that chemoautotrophy is an important
alternative to photosynthesis for carbon cycling in desiccated desert soils. Analysis
of the transcriptional levels of key N-cycling genes provided strong evidence that soil
nitrate was the dominant nitrogen input source. Transcriptional network analyses and
taxon-resolved functional profiling suggested that nutrient acquisition processes, and
not diurnal environmental variation, were the main drivers of community activity in
hyperarid Namib Desert soil. While we also observed significant levels of expression
of common stress response genes, these genes were not dominant hubs in the
co-occurrence network.
