Romero Blanch, Ferran

Universitat Autònoma de Barcelona. Facultat de Biociències

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    MICROBIOLOGY OF A SUBGLACIAL LAKE: THE LAKE VOSTOK Ferran Romero Blanch  INTRODUCTION: Lake Vostok is the largest and deepest subglacial body of water in Antarctica. It has an area of 14000Km2 and a volume of 5600Km3. Nowadays, it is accepted that it has been buried under glacial ice for 14-15 millions of years (Figure 1). Discovered between 1950 and 1960, it has been recently reported that it forms a complex ecosystem with both prokaryotic and eukaryotic microorganisms1,2.  The living forms here have evolved to survive in an extremely oligotrophic, hyperbaric, cold and dark environment. Main characteristics of Lake Vostok Temperature: -2°C  Pressure: 350atm (as it is covered by a 4-kilometer-thick layer of glacial ice) Nutrient availability: very slow Light: absent  The ice above Lake Vostok freezes forming a 220m layer of accreted ice. It is generally accepted that this 220m layer of accreted ice reflects the contents into the lake and, because of this, it has been under study during the last 30 years. Ice accreting near the embayment has higher concentrations of ions, biomass and solid inclusions and it is known as type I accretion ice. The ice that forms over open water contains lower concentrations of biomass and ions and has been termed type II accretion ice3 (Figure 2). Mainly because of this, type I accretion ice shows more richness and abundance of sequences. OBJECTIVES The aim of the present review is to describe the communities present in a subglacial lake (the Lake Vostok).  It is also objective of this review to describe the use of ice-binding proteins as a method to survive in extremely cold environments. As it is shown in the graphic (Figure 3), the main known phyla present in lake Vostok accretion ice are Firmicutes, Proteobacteria and Actinobacteria (determined by the sequence of 16S rDNA gene). The members of Firmicutes found in accretion ice include species such as Paenibacillus sp. and Bacillus sp. (soil inhabitants), Carnobacterium sp., Macrococus sp., and Clostridium sp. (water inhabitants usually associated with marine metazoan). Proteobacteria include species previously found in other Antarctic environments (Sphingomonas sp.) and symbionts such as Aquabacterium sp., Pelomonas saccharophila, Comamonas sp., Verminephrobacter sp. and Curvibacter sp. The phylum Actinobacteria it is also represented in lake Vostok accretion ice as it has been reported the presence of bacteria also found in seafood (Brachybacterium sp.) and a large number of fish-associated actinobacteria (Mobilicoccus pelagius, Renibacter salmonarium and Mycobacterium marinum). Several analyses of melted ice samples with both fluorescence and scanning microscopes have been carried out and a large number of different morphologies have been reported, as shown in the micrographs below1,2,3 (Figure 4). Figure 1. Location of lake Vostok under Antarctic glacial ice1. Figure 2. Location of type I and type II accretion ice above lake basin3. Figure 3. Taxonomic proportions from 16S rDNA metagenomic data including only sequences that have identities between 99 and 100%. Data from reference 3.  Broad taxonomic proportions (type I accretion ice)5%4%5%13%17%56%UnidentifiedFirmicutesProteobacteriaActinobacteriaother BacteriaEukaryotaFigure 4. Fluorescence and scanning electron micrographs of cells found in accretion ice2. Ice-binding proteins (IBP) are a useful method to cope with freezing conditions. IBP are peptides that specifically bind to and inhibit the recrystallization of ice. The recrystallization of ice is the growth of ice crystals and it has negative consequences to living forms. IBPs have been demonstrated to be produced by microbes from the family Flavobacteriaceae isolated from Vostok ice core and other organisms.  Its recrystallization inhibition (RI) activity has been determined by measuring the ability of a solution (containing the IBP) to prevent distortions in a growing ice crystal4 (Figure 5). 30 min                             21 h  IBP-   IBP+ Figure 5. RI activity. In a solution containing ice-binding protein (IBP+) recrystallization of ice doesn’t take place4. 1. Christner, B. C., Mosley-Thompson, E., Thompson, L. G., & Reeve, J. N. (2001). 2. D’Elia, T., Veerapaneni, R., & Rogers, S. O. (2008). 3. Shtarkman, Y. M. et al (2013).  4. Raymond, J. a, Christner, B. C., & Schuster, S. C. (2008).  CONCLUSIONS: Far from being sterile, lake Vostok accretion ice shows a diverse set of sequences related to eukaryotic and prokaryotic organisms despite the fact that it is a extremely cold, oligotrophic and hyperbaric environment. The majority of the sequences found are unidentified. The main prokaryotic known phyla are: Actinobacteria Firmicutes Proteobacteria Microbes living here have developed an efficient method to inhibit the recrystallization of ice, the production of a molecules that bind ice crystals called ice-binding proteins (IBP) 

Microbiology of a subglacial lake : the lake Vostok

http://ddd.uab.cat/pub/tfg/2014/126392/TFG_ferranromeroblanch.pdf

Microbiology of a subglacial lake : the lake Vostok

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