Microbial community composition and ecology of an acidic aquatic environment: The Tinto River, Spain

We studied the correlation between physicochemical and biological character istics of an acidic river, the Tinto River, in Southwestern Spain. The Tint o River is an extreme environment characterized by its low pH (mean of 2.2) and high concentrations of heavy metals (Fe 2.3 g/L, Zn 0.22 g/L, Cu 0.11 g/L). These extreme conditions are the product of the metabolic activity of chemolithotrophic microorganisms, including iron- and sulfur-oxidizing bac teria, that can be found in high concentrations in its waters. The food cha in in the river is very constrained and exclusively microbial. Primary prod uctivity in the Tinto River is the sum of photosynthetic and chemolithotrop hic activity. Heterotrophic bacteria and fungi are the major decomposers an d protists are the major predators. A correlation analysis including the ph ysicochemical and biological variables suggested a close relationship betwe en the acidic pH values and abundance of both chemolithotrophic bacteria an d filamentous fungi. Chemolithotrophic bacteria correlated with the heavy m etals found in the river. A principal component analysis of the biotic and abiotic variables suggested that the Tinto River ecosystem can be described as a function of three main groups of variables: pH values, metal concentr ations, and biological productivity.