Microbial Community Structure Driven by a Volcanic Gradient in Glaciers of the Antarctic Archipelago South Shetland

Abstract

It has been demonstrated that the englacial ecosystem in volcanic environments is inhabited by active bacteria. To know whether this result could be extrapolated to other Antarctic glaciers and to study the populations of microeukaryotes in addition to those of bacteria, a study was performed using ice samples from eight glaciers in the South Shetland archipelago. The identification of microbial communities of bacteria and microeukaryotes using 16S rRNA and 18S rRNA high throughput sequencing showed a great diversity when compared with microbiomes of other Antarctic glaciers or frozen deserts. Even the composition of the microbial communities identified in the glaciers from the same island was different, which may be due to the isolation of microbial clusters within the ice. A gradient in the abundance and diversity of the microbial communities from the volcano (west to the east) was observed. Additionally, a significant correlation was found between the chemical conditions of the ice samples and the composition of the prokaryotic populations inhabiting them along the volcanic gradient. The bacteria that participate in the sulfur cycle were those that best fit this trend. Furthermore, on the eastern island, a clear influence of human contamination was observed on the glacier microbiome.

Keywords: 16S/18S rRNA high throughput sequencing; Antarctica; astrobiology; biodiversity; biogeochemistry; cryosphere microbiome; ecology; glacier.

Figure 1

Location of sampling sites in South Shetland Islands, Antarctica. Satellite photographs of Antarctic continent (A) and Antarctic Peninsula (B) with South Shetland Islands boxed (ESA copyright-CC BY-SA IGO3.0; https://creativecommons.org/licenses/by-sa/3.0/igo/). (C) Map of Deception, Livingston, Greenwich, and King George Islands indicating the studied glaciers. (D) Volcanic gradient and setting of samples collected at glaciers: 1 Rojo; 2 Macaroni; 3 Johnson; 4 Hurd; 5 Quito; 6 Traub; 7 Ecology; 8 Machu Picchu. Ash and lava embedded in glacial ice can be observed along the gradient in the lower images.

Figure 2

Composition of microbial communities. Relative abundances of major taxa of (A) bacteria and (B) microeukaryotes in the englacial ecosystem based on 16S and 18S rRNA gene sequencing.

Figure 3

The relative abundances of the microbial phyla of bacteria and microeukaryotes were analyzed by detrended corresponded analysis (DCA). The diagram displays triangles that represent phyla of bacteria (orange) and microeukaryotes (green). Venn diagrams cluster and discriminate areas in which bacteria (orange diagrams) or microeukaryotes (green diagrams) are more abundant.

Figure 4

Canonical correspondence analysis (CCA) of the microbial phyla with respect to the distance from the volcano. CCA of phyla of bacteria (A) and microeukaryotes (B) identified in glaciers with respect to the distance from the volcano. The diagram displays triangles that represent taxonomic groups. (C) CCA of all the microbial phyla (bacteria and microeukaryotes) identified in glaciers with respect to the distance from the volcano. The diagram displays orange triangles for bacteria and green triangles for microeukaryotes. Venn diagram clusters an area in which microeukaryotes are more abundant.

Figure 5

CCA of the microbial phyla of (A) bacteria and (B) microeukaryotes identified in glaciers with respect to the concentration of nutrients (NH₄⁺, NO₂^-, NO₃^-, total dissolved nitrogen (TDN), soluble reactive phosphorous (SRP), and dissolved organic carbon (DOC)).

Figure 6

CCA of the microbial phyla of (A) bacteria and (B) microeukaryotes identified in glaciers with respect to the concentration of main elements (As, C, Ca, Cd, Cl, Fe, K, Mg, Na, S).

Figure 7

Insights into biogeochemical cycles based on the volcanic gradient along South Shetland glaciers. Some key members of carbon, nitrogen, iron, and sulfur cycles in glaciers were represented at the genus level (bacteria colored in orange and microeukaryotes colored in green). The size of the circles was calculated by the number of operational taxonomic units (OTUs) occurring at a frequency of more than 3% at sample points: (A) sample points 1 and 2, (B) sample points 3 to 6 and (C) sample points 7 and 8.