Periglacial and volcanic environments are considered terrestrial analogs of Mars with regard to astrobiological characteristics due to their specific set of extreme features. Ojos del Salado, the highest volcano on Earth (6893 m a.s.l.), is surrounded by several craters, one of which harbors the highest known altitude lake (6480 m a.s.l.), which is influenced by a rare combination of extreme environmental factors, that is, low mean temperature, permafrost, fumarolic activity, acidity, and extreme low organic matter content. To assess the genetic diversity and ecological tolerance of bacteria, samples were taken in February 2016 from the sediments covered with acidic cold (pH 4.88, 3.8°C) and warm (pH 2.08, 40.8°C) water. As a control, a nonvolcanic high-altitude lake (at 5900 m a.s.l.) was also studied by both cultivation-based and next-generation DNA sequencing methods. Isolates from the crater lake showed tolerance toward acidic pH values, unlike isolates from the nonvolcanic lake. Illumina MiSeq sequencing of the 16S rRNA gene exposed simplified, although characteristically different, bacterial communities in the warm and cold water-saturated sediments. In the fumarolic creek sediments, acidophilic iron oxidizers (Ferrithrix, Gallionella) and iron reducers (Acidiphilium) were abundant, and bacteria involved in the sulfur oxidation (Hydrogenobaculum, Thiomonas) and reduction (Desulfosporosinus) were also detected. Therefore, we propose an integrated model that addresses the potential role of bacteria in the sulfur and iron geomicrobiological cycles.
Keywords: Extreme habitats; Extremophilic bacteria; Fumaroles; High-altitude lake; Iron biochemical cycle; Mars analogs.