Lipid signatures of acidophilic microbial communities in an extreme acidic environment – Río Tinto, Spain

The Rيo Tinto in Spain is a naturally occurring example of an extreme environment, characterized by a low mean pH of ca. 2.2 and high heavy metal concentration, consequences of pyrite oxidation of the source rock and strong buffering capacity of the abundant iron. To describe the microbial community, we combined the analysis of intact polar lipids (IPLs) and total fatty acids (FAs) with a carbon isotope labeling experiment to trace autotrophic processes. IPL analysis revealed clear differences between the four different sampling sites, while also indicating the presence of abundant eukaryotic algal and fungal biomass. Lipid-based estimates of the prokaryotic contribution were between 10% and 32%. We investigated the lipid composition of the predominant bacteria to determine their lipid footprints in the environmental samples. The relatively 13C-enriched carbon isotopic composition of the iso- and anteiso-C15 and C17 FAs suggests that the chemolithoautotrophic community members in sediments underlying phototrophic mats were limited by CO2 availability. The isotopic composition of cycC19:0/C19:1 was in the range for major heterotrophs, indicating an origin in acidophilic chemolithoheterotrophs. Labeling experiments with 13C labeled HCO 3 - indicated that photoautotrophic eukaryotes are most important for carbon fixation in Rيo Tinto.