Abstract
Glaciers and their microbiomes are exceptional witnesses of the environmental conditions from remote times. Climate change is threatening mountain glaciers, and especially those found in southern Europe, such as the Monte Perdido Glacier (northern Spain, Central Pyrenees). This study focuses on the reconstruction of the history of microbial communities over time. The microorganisms that inhabit the Monte Perdido Glacier were identified using high-throughput sequencing, and the microbial communities were compared along an altitudinal transect covering most of the preserved ice sequence in the glacier. The results showed that the glacial ice age gradient did shape the diversity of microbial populations, which presented large differences throughout the last 2000 years. Variations in microbial community diversity were influenced by glacial conditions over time (nutrient concentration, chemical composition, and ice age). Some groups were exclusively identified in the oldest samples as the bacterial phyla Fusobacteria and Calditrichaeota, or the eukaryotic class Rhodophyceae. Among groups only found in modern samples, the green sulfur bacteria (phylum Chlorobi) stood out, as well as the bacterial phylum Gemmatimonadetes and the eukaryotic class Tubulinea. A patent impact of human contamination was also observed on the glacier microbiome. The oldest samples, corresponding to the Roman Empire times, were influenced by the beginning of mining exploitation in the Pyrenean area, with the presence of metal-tolerant microorganisms. The most recent samples comprise 600-year-old ancient ice in which current communities are living.
Highlights
Glaciers are considered authentic ecosystems inhabited by microorganisms that maintain active biochemical routes and play a key role in biogeochemical cycles (Boetius et al, 2015; Garcia-Lopez et al, 2016; Anesio et al, 2017)
It is worth highlighting the increase in the concentration of soluble reactive phosphorus (SRP) in the samples MP40 and MP50, which coincides with an increase in these samples of insoluble particles (Supplementary Figure 3)
The low concentration of these elements in Monte Perdido Glacier (MPG) samples throughout the chronological sequence could indicate their disappearance from glacier surface layers due to its continuous melting associated to last decades
Summary
Glaciers are considered authentic ecosystems inhabited by microorganisms that maintain active biochemical routes and play a key role in biogeochemical cycles (Boetius et al, 2015; Garcia-Lopez et al, 2016; Anesio et al, 2017) All these microorganisms, especially bacteria and algae, are the basis of food webs that allow the life of more complex organisms, such as cold-tolerant insects and copepods within glacial ice (Kohshima et al, 2002). The Antarctic coastal glaciers have been drilled in search of cultivable and physiologically active organisms (Antony et al, 2012; Martinez-Alonso et al, 2019) In these reports, the highest numbers of microorganisms in both Arctic and Antarctic ice cores were found in sections that were deposited during ancient times of low atmospheric CO2, low global temperatures, and low levels of atmospheric dust (Knowlton et al, 2013). In mountain glaciers, snow algae were identified from ice cores recovered in Nepal (Yoshimura et al, 2000), as well as bacterial isolates were collected from the Tibetan Plateau (Zhang et al, 2008; Shen et al, 2018)
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