The microbial diversity in arid zone aquatic ecosystems in central Australia

Arid regions dominate large parts of the world. Sparsely distributed perennial freshwater systems in arid central Australia form an important refuge for migrating species and act as a biotic reservoir under adverse conditions. They are rarely hydrologically connected, severely restricting dispersal for obligate aquatic organisms rendering the biota of these habitats vulnerable to environmental change. Despite the important role of microbes in driving biogeochemical processes, little is known about their composition and spatial patterns in and across these freshwater systems. The aim of this study was to assess the diversity and spatial distribution of Bacteria and Archaea in waterbodies in arid central Australia. Using 16s-rRNA gene amplicon sequencing we analysed the structure of microbial communities in biofilms and the water column from eight waterbodies along a geographic axis across two major drainage divisions.We found a similarity decay with increasing distance for the water microbial assemblages with many cosmopolitan taxa common to aquatic ecosystems. The biofilm microbiota was enriched with heterotrophic and chemoorganotrophic bacteria able to degrade complex organic materials affirming their important role in detrital food webs. Biofilms showed considerable within-site variability in particular for perennial waterbodies and also clustered according to benthic substrate. Electrical conductivity and pH partly explained the composition of the microbial communities, but only the water microbiota was associated with water isotopic signatures. Temporary waterbodies fed by surface water contained significantly more bacteria of heat and arid resilient microbial taxa widespread in soils.