Metabolomics of Dry Versus Reanimated Antarctic Lichen-Dominated Endolithic Communities

Abstract

Cryptoendolithic communities are almost the sole life form in the ice-free areas of the Antarctic desert, encompassing among the most extreme-tolerant organisms known on Earth that still assure ecosystems functioning, regulating nutrient and biogeochemical cycles under conditions accounted as incompatible with active life. If high-throughput sequencing based studies are unravelling prokaryotic and eukaryotic diversity, they are not yet characterized in terms of stress adaptations and responses, despite their paramount ecological importance. In this study, we compared the responses of Antarctic endolithic communities, with special focus on fungi, both under dry conditions (i.e., when dormant), and after reanimation by wetting, light, and optimal temperature (15 °C). We found that several metabolites were differently expressed in reanimated opposite sun exposed communities, suggesting a critical role in their success. In particular, the saccharopine pathway was up-regulated in the north surface, while the spermine/spermidine pathway was significantly down-regulated in the shaded exposed communities. The carnitine-dependent pathway is up-regulated in south-exposed reanimated samples, indicating the preferential involvement of the B-oxidation for the functioning of TCA cycle. The role of these metabolites in the performance of the communities is discussed herein.

Keywords: Antarctica; adaptation; cryptoendolithic communities; extremophiles; sun exposure; untargeted metabolomics.

Figure 1

(A) Map of Antarctica. Red symbol indicates the study area, Finger Mt. (McMurdo Dry Valleys, Southern Victoria Land, Continental Antarctica); (B) Northern and (C) southern exposed rock surfaces; (D) outline of reactivation experiment. Credit by Italian National Antarctic Research Program (PNRA).

Figure 2

(A) The cloud plot shows perturbations in metabolism caused by the reactivation of northern exposed rock samples. Each pathway is displayed as a circle, with the x axis representing the percentage of metabolite overlap within that pathway and the y axis representing increased pathway significance calculated from the pathway analysis. The radius of each circle is proportional to the total number of metabolites in the pathway. Pathways with a higher percent overlap of metabolites and statistical significance will appear in the upper right corner (saccharopine pathway; spermine and spermidine degradation I; lysine-ketoglutarate reductase; pipecolate pathway). (B) Intermediates of the saccharopine pathway were up regulated after metabolic machinery reactivation. (C) Metabolomic profile of spermine and spermidine pathway. p-values less than 0.05 were considered significant; p-values marked *** p < 0.001.

Figure 3

(A) The cloud plot shows perturbations in cellular metabolism caused by the reactivation of southern exposed rock samples. Each pathway is displayed as a circle, with the x axis representing the percentage of metabolite overlap within that pathway and the y axis representing increased pathway significance calculated from the pathway analysis. The radius of each circle is proportional to the total number of metabolites in the pathway. Pathways with a greater percent overlap of metabolites and statistical significance are found in the upper right corner. (B) Overview of L-carnitine biosynthesis metabolism. p-values < 0.05 are considered significant; p-values marked *** p < 0.001.

Figure 4

(A) The cloud plot shows perturbations in cellular metabolism between northern and southern exposed reactivated rocks. Each pathway is displayed as a circle, with the x axis representing the percentage of metabolite overlap within that pathway and the y axis representing increased pathway significance calculated from the pathway analysis. The radius of each circle is proportional to the total number of metabolites in the pathway. Tricarboxylic acid cycle (TCA) with a greater percent overlap of metabolites and statistical significance is found in the upper right corner. (B) Intermediates of TCA cycle measured in northern and southern exposed reactivated rocks. p-values < 0.05 are considered significant; p-values marked *** p < 0.001.