Cold adapted desiccation-tolerant bacteria isolated from polar soils presenting high resistance to anhydrobiosis

Life on Earth is strictly dependent on liquid water. In polar terrestrial environments, water exists in solid state during almost the entire year. Polar microorganisms have not only to adjust their metabolism to survive at subzero temperatures, but also need to cope with extremely dry conditions. We investigated the presence of desiccation-adapted bacteria in Arctic permafrost and Antarctic surface soils and characterized their survivability to dryness. We selected desiccation tolerant cells by treating the soils with chloroform prior to cultivation, in order to mimic the stress of low water activity for long periods. From over 1000 colonies from different samples, 23 unique strains were selected and identified as members of phyla Firmicutes, Proteobacteria and Actinobacteria. About 60% of the strains survived after 50 days in anhydrobiosis. The competence to withstand desiccation varied between close related strains isolated from different locations, bringing the question if environmental conditions may play a role in the observed desiccation tolerance. Survivability was also affected by the solution in which the cells were suspended before drying; R2B medium being more protective than water. This is the first time that chloroform was used to select desiccation tolerant microorganisms from polar soils. The collection of polar microorganisms described herein opens the possibility of further experiments aiming to investigate the resistance mechanisms of polar anhydrobionts. Desiccation tolerance is fundamental to the survivability of microorganisms to the space environment and at the surface of thin-atmosphere planets like Mars. Therefore, the selected strains may open a road to better understand the limits of cold adapted life on Earth and beyond, and compare mechanisms of resistance with anhydrobionts from divergent extreme environments.

Diversity and activity of microorganisms in Antarctic polar soils

The study is focused on microbiological analyses in polar soils in selected monitoring sites in Livingstone Island, Antarctica region. The analyses include determination of the quantity and qualitative composition of the heterotrophic block of soil microflora (non-spore-forming bacteria, bacilli, actinomycetes, micromycetes, bacteria absorbing mineral nitrogen), insofar as it plays a major role in the element cycling and soil formation processes. Aerobic (rapidly and slowly growing) and anaerobic groups of soil microorganisms were investigated and the biogenicity (total microflora) and the rate of mineralisation processes (mineralisation coefficient) were determined. Mostly non-spore-forming aerobic bacteria, followed by actinomycetes, are dominant in determining the biogenicity of the studied polar soils. The rearrangement of the microorganisms in the composition of the total microflora by degree of dominance indicates the participation of all the studied groups of microorganisms in most sites in the initial and final stages of the decomposition of organic matter. The mineralisation of soils is most active in sites with vegetation cover. The established pigmentation in aerobic microorganisms is probably due to their good adaptation and protection under extreme polar conditions, while the absence of oxygen impedes the formation of pigments.

13C NMR and ESR Characterization of Humic Substances Isolated from Soils of Two Siberian Arctic Islands

Humic acids (HAs) and fulvic acids (FAs) of two Polar soils were investigated by13C NMR and ESR spectroscopies, investigating the degree of humification and the molecular structure. One soil, from Bolshoi Lyakhovsky Island, contains two humus horizons: modern and buried. The other soil, from Wrangel Island, had only one modern humus horizon. The HAs and FAs of the two soils investigated show essential differences. The HAs show fewer oxygen-containing groups in comparison with the FAs, whereas the degree of aromaticity is two or three times higher in the HAs. The13C NMR data also show that HAs are very different from FAs in terms of their molecular composition and hydrophobicity. Humification in the Arctic is limited by the very low content of lignin-derived compounds, due to the restricted vascular flora. As a result, the HAs, isolated from Polar soils, are more similar to the corresponding FAs than to the typical HAs of temperate soils. This was confirmed by ESR data, which show similar levels of free radical concentration for HAs and FAs and are related to the low level of aromaticity of both materials investigated. Apparently, the humification process in the soils of Polar Arctic deserts is in an initial stage.