Taxonomic diversity and environmental tolerance of cultivable extremophilic bacteria from a high-altitude meltwater pond on Ojos del Salado (Chile).

Earth harbors unique environments where only microorganisms adapted to extreme conditions, known as extremophiles, can survive. This study focused on a high-altitude meltwater pond, located in the Puna de Atacama, Dry Andes. The extremophilic bacteria of this habitat must adapt to a range of extremities, including cold and dry climate, high UV radiation, high daily temperature fluctuations, low-nutrient availability, and negative water balance. This study aimed to explore the taxonomic diversity of cultivable extremophilic bacteria from sediment samples of a desiccated, high-altitude, meltwater pond using media with different organic matter contents and different incubation temperatures. Based on the 16S rRNA gene sequence analysis, the isolates were identified as members of the phyla Actinobacteria, Proteobacteria, and Firmicutes. The most abundant genera were Arthrobacter and Pseudoarthrobacter. The isolates had oligocarbophilic and psychrotrophic properties, suggesting that they have adapted to the extreme environmental parameters of their natural habitats. The results indicate a positive correlation between nutrient concentration and temperature tolerance.

Effects of Active Volcanism on Bacterial Communities in the Highest-Altitude Crater Lake of Ojos del Salado (Dry Andes, Altiplano-Atacama Region).

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.

Bacterial Diversity of a High-Altitude Permafrost Thaw Pond Located on Ojos del Salado (Dry Andes, Altiplano-Atacama Region).

Microbial ecology of permafrost, due to its ecological and astrobiological importance, has been in the focus of studies in past decades. Although permafrost is an ancient and stable environment, it is also subjected to current climate changes. Permafrost degradation often results in generation of thaw ponds, a phenomenon not only reported mainly from polar regions but also present in high-altitude permafrost environments. Our knowledge about microbial communities of thaw ponds in these unique, remote mountain habitats is sparse. This study presents the first culture collection and results of the next-generation DNA sequencing (NGS) analysis of bacterial communities inhabiting a high-altitude permafrost thaw pond. In February 2016, a permafrost thaw pond on the Ojos del Salado at 5900 m a.s.l. (meters above sea level) was sampled as part of the Hungarian Dry Andes Research Programme. A culture collection of 125 isolates was established, containing altogether 11 genera belonging to phyla Bacteroidetes, Actinobacteria, and Proteobacteria. Simplified bacterial communities with a high proportion of candidate and hitherto uncultured bacteria were revealed by Illumina MiSeq NGS. Water of the thaw pond was dominated by Bacteroidetes and Proteobacteria, while in the sediment of the lake and permafrost, members of Acidobacteria, Actinobacteria, Bacteroidetes, Patescibacteria, Proteobacteria, and Verrucomicrobia were abundant. This permafrost habitat can be interesting as a potential Mars analog.