Microbial Assemblages in Pressurized Antarctic Brine Pockets (Tarn Flat, Northern Victoria Land): A Hotspot of Biodiversity and Activity.

Maria Papale,Gabriella Caruso,Angelina Lo Giudice,Carmen Rizzo,Anderson S Cabral,Alessandro C Rappazzo,Giovanna Maimone,Rosabruna La Ferla,Maurizio Azzaro,Concetta Gugliandolo,Mauro Guglielmin,Antonella Conte,Rodolfo Paranhos,Vincenzo Romano Spica

doi:10.3390/microorganisms7090333

Abstract

Two distinct pressurized hypersaline brine pockets (named TF4 and TF5), separated by a thin ice layer, were detected below an ice-sealed Antarctic lake. Prokaryotic (bacterial and archaeal) diversity, abundances (including virus-like particles) and metabolic profiles were investigated by an integrated approach, including traditional and new-generation methods. Although similar diversity indices were computed for both Bacteria and Archaea, distinct bacterial and archaeal assemblages were observed. Bacteroidetes and Gammaproteobacteria were more abundant in the shallowest brine pocket, TF4, and Deltaproteobacteria, mainly represented by versatile sulphate-reducing bacteria, dominated in the deepest, TF5. The detection of sulphate-reducing bacteria and methanogenic Archaea likely reflects the presence of a distinct synthrophic consortium in TF5. Surprisingly, members assigned to hyperthermophilic Crenarchaeota and Euryarchaeota were common to both brines, indicating that these cold habitats host the most thermally tolerant Archaea. The patterns of microbial communities were different, coherently with the observed microbiological diversity between TF4 and TF5 brines. Both the influence exerted by upward movement of saline brines from a sub-surface anoxic system and the possible occurrence of an ancient ice remnant from the Ross Ice Shelf were the likely main factors shaping the microbial communities.

Highlights

In continental Antarctica, brines are hypersaline solutions generally found within permafrost [1,2,3]
The virus-like particle (VLP) abundances were in the order of 1010 VLP L−1 and higher counts were obtained in TF4 (3.47 ± 0.18 × 1010 VLP L−1) than TF5 (2.57 ± 0.08 × 1010 VLP L−1)
The most likely hypotheses to explain the microbial community differentiation recorded in the examined brines could be the following: (i) the different chemical and physical composition of the brines; (ii) the presence of a barrier represented by a thin layer of ice; and (iii) the different geological origins of the brines

Summary

Introduction

In continental Antarctica, brines are hypersaline solutions generally found within permafrost [1,2,3]. The discovery of brines in the sub-surfaces of Mars and Jupiter’s moon Europa makes Antarctic brines attractive as terrestrial analogue counterparts and potential astrobiological targets [15] The occurrence of such liquids is central to understand the potential for extant life on the Red Planet [16], and the exploration of psychrophiles on Earth becomes significant for our comprehension of the boundaries of life on Earth or elsewhere in our solar system [5,17,18,19,20,21]. Such chemoautotrophs utilize molecular hydrogen and carbon dioxide and produce methane as a waste product, making conceivable, their existence on Mars [22]

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