Isolation and Distribution of an Iron-Oxidizing Thermophilic Acidophile from Acid Sulfate Chloride Geothermal Springs of Yellowstone National Park

Many acidic geothermal springs in Yellowstone National Park (YNP) contain significant concentrations of dissolved Fe(II) at the source. The oxidation of Fe(II) with oxygen as an electron acceptor is energetically favorable in many geothermal springs, consequently, Fe(II) may be an important electron donor driving primary production in some thermophilic habitats. The biomineralization of Fe(III)-oxides of varying crystallinity and structure is a common process in acid-sulfate and acid-sulfate-chloride geothermal springs. However, little is known regarding the microbial populations that are actively involved in this process and whether these organisms may be utilizing Fe(II) as an electron donor for energy conservation. Based on spring conditions and phylogenetic surveys, enrichments were established to isolate Fe(II)-oxidizing microorganisms from acidic geothermal springs over temperature ranges from 55-80 C. An Fe(II)-oxidizing Metallosphaera-like organism with a pH optima of 2.8 and a temperature optima of 65 C has been isolated from one such spring. The full-length 16S rDNA sequence of this organism is closely related to numerous 16S rDNA clones that have been characterized in a variety of acidic Fe(III)-oxide mats from YNP, where gradients in dissolved oxygen likely control the distribution and activity of this organism. Furthermore, the isolate and corresponding clones cluster separately from the currently cultivated closest Metallosphaera relatives. The properties and distribution of this organism suggest that it is a common archaeal member of microbial communities in acidic thermal environments, and may be responsible for the observed biomineralization of different types of Fe(III)-oxide phases occurring in YNP geothermal systems.