Microbial communities of acidic hypersaline sediments

Groundwater and surface waters with low pH and high concentration of sodium chloride are widely spread in southern Western Australia (WA). Litter is known about the microbial communities thriving or adapting in such environments and their roles in water acidification and salinity genesis. We aimed to investigate the microbial community compositions in the sediments from the acidic (pH ~3) and hypersaline (> 3.5% NaCl) West Dalyup River in WA. Large amount of NaCl, K, Fe(II), Al, Mg and sulfate were brought by the groundwater into the surface runoff at the waterhead (site WH), and the sediment was dominated by the Fe(III)-containing mineral K-jarosite, whereas schwertmannite was identified as the main mineral in the ‘iron crust’-like river sediment 3.6 km downstream (site DS). Quantitative PCR revealed a dominance of Bacteria over Archaea at both sites. The 16S rRNA gene biodiversity analyses revealed the Proteobacteria as the most dominant phylum in both sediments and the frequent occurrence of the acidophilic Alphaproteobacteria Acidiphilium and Acidocella. The yet uncultured archaeal lineage named Aplasma belonging to the Thermoplasmatales was identified in both sediment samples and suggested to be the sole functioning Fe(II)-oxidizing group in this river. Acidiphilium stain AusYE3-1 was isolated from the sediment of site WH. Stain AusYE3-1 was able to grow as a heterotroph in the acidic medium (pH 3) containing up to 6% NaCl. In addition, growth was not observed in anaerobic medium containing additional NaCl. Cells of strain AusYE3-1 formed high aggregation of characteristic cell chains when cultured in NaCl containing media, indicating that AusYE3-1 might eliminate the effects of high salt content by reducing its surface area through alteration of cell structure. The discovery of the Acidiphilium-dominated microbial communities in the sediments and the observation of the isolate had advanced our knowledge of the ecology of the acidic hypersaline environments and may contribute to the fundamental understanding of the origin of the acidity and salinity in WA.