The hidden microbial ecosystem in the perennial ice from a Pyrenean ice cave

Abstract

Over the last years, perennial ice deposits located within caves have awakened interest as places to study microbial communities since they represent unique cryospheric archives of climate change. Since the beginning of the twentieth century, the temperature has gradually increased, and it is estimated that by the end of this century the increase in average temperature could be around 4.0°C. In this context of global warming the ice deposits of the Pyrenean caves are undergoing a significant regression. Among this type of caves, that on the Cotiella Massif in the Southern Pyrenees is one of the southernmost studied in Europe. These types of caves house microbial communities which have so far been barely explored, and therefore their study is necessary. In this work, the microbial communities of the Pyrenean ice cave A294 were identified using metabarcoding techniques. In addition, research work was carried out to analyze how the age and composition of the ice affect the composition of the bacterial and microeukaryotic populations. Finally, the in vivo effect of climate change on the cellular machinery that allow microorganisms to live with increasing temperatures has been studied using proteomic techniques.

Keywords: Pyrenees; environmental variables; global warming; ice cave; microbial community profiling; next-generation sequencing; proteomics.

FIGURE 1

Geological setting of samples. (A) Location of the A294 ice cave in the Central Pyrenees. (B) Photograph showing the main entrance of the cave. (C) Profile view of the A294 ice cave showing the snow ramp and the position of the ice body, modified from Belmonte-Ribas et al. (2014).

FIGURE 2

Stratigraphy and ice sampling. (a) Stratigraphy and chronology of the ice deposit in 2011 (Sancho et al., 2018) and 2015 (Leunda et al., 2019) together with the position of the samples taken in 2018 for the present study. (b) View of the ice body in 2018 and the approximate position of the samples taken. (c) Ice sampling using the ice auger. M1, M2, M3, and M4, names of the samples; Cal. BP, calibrated years before the present.

FIGURE 3

Microbial community distribution in the cave ice samples at the phylum level. Relative abundances of major taxa of bacteria and microeukaryotes based on (A) 16S rRNA and (B) 18S rRNA gene sequencing data, respectively.

FIGURE 4

Principal component analysis (PCA). Scatterplot of (A) bacterial phyla, (B) bacterial genera, (C) eukaryotic phyla, and (D) eukaryotic genera.

FIGURE 5

Pie charts comparing protein distribution at 0 and 4°C. (A–D) Pie charts corresponding to samples M1–M4, respectively. (E) Total protein distribution at 0 and 4°C.

FIGURE 6

Model of the metabolic potentials between dominant microorganisms in the ice cave. Some key members were represented at genus level (Prokaryotes in black, Eukaryotes in green).