Aerobiology in High Latitudes: Evidence of Bacteria Acting as Tracer of Warm Air Mass Advection reaching Northern Antarctic Peninsula.

Despite the extent use of geochemical tracers to track warm air mass origin reaching the Antarctic continent, we present here evidences that microorganisms being transported by the atmosphere and deposited in fresh snow layers of Antarctic ice sheets do act as tracers of air mass advection from the Southern Patagonia region to Northern Antarctic Peninsula. We combined atmospheric circulation data with microorganism content in snow/firn samples collected in two sites of the Antarctic Peninsula (King George Island/Wanda glacier and Detroit Plateau) by using flow cytometer quantification. In addition, we cultivated, isolated and submitted samples to molecular sequencing to precise species classification. Viable gram-positive bacteria were found and recovered in different snow/firn layers samples, among dead and living cells, their number concentration was compared to northern wind component, stable isotopes of oxygen, d18O, and the concentration of crustal elements (Fe, Ti and Ca). Use of satellite images combined with air mass back-trajectory analysis obtained from the NOAA/ HYSPLIT model corroborated the results.

Brine assemblages of ultrasmall microbial cells within the ice cover of Lake Vida, Antarctica.

The anoxic and freezing brine that permeates Lake Vida's perennial ice below 16 m contains an abundance of very small (≤0.2-µm) particles mixed with a less abundant population of microbial cells ranging from >0.2 to 1.5 µm in length. Fluorescent DNA staining, electron microscopy (EM) observations, elemental analysis, and extraction of high-molecular-weight genomic DNA indicated that a significant portion of these ultrasmall particles are cells. A continuous electron-dense layer surrounding a less electron-dense region was observed by EM, indicating the presence of a biological membrane surrounding a cytoplasm. The ultrasmall cells are 0.192 ± 0.065 µm, with morphology characteristic of coccoid and diplococcic bacterial cells, often surrounded by iron-rich capsular structures. EM observations also detected the presence of smaller unidentified nanoparticles of 0.020 to 0.140 µm among the brine cells. A 16S rRNA gene clone library from the brine 0.1- to 0.2-µm-size fraction revealed a relatively low-diversity assemblage of Bacteria sequences distinct from the previously reported >0.2-µm-cell-size Lake Vida brine assemblage. The brine 0.1- to 0.2-µm-size fraction was dominated by the Proteobacteria-affiliated genera Herbaspirillum, Pseudoalteromonas, and Marinobacter. Cultivation efforts of the 0.1- to 0.2-µm-size fraction led to the isolation of Actinobacteria-affiliated genera Microbacterium and Kocuria. Based on phylogenetic relatedness and microscopic observations, we hypothesize that the ultrasmall cells in Lake Vida brine are ultramicrocells that are likely in a reduced size state as a result of environmental stress or life cycle-related conditions.

Microbial life at -13 °C in the brine of an ice-sealed Antarctic lake.

The permanent ice cover of Lake Vida (Antarctica) encapsulates an extreme cryogenic brine ecosystem (-13 °C; salinity, 200). This aphotic ecosystem is anoxic and consists of a slightly acidic (pH 6.2) sodium chloride-dominated brine. Expeditions in 2005 and 2010 were conducted to investigate the biogeochemistry of Lake Vida's brine system. A phylogenetically diverse and metabolically active Bacteria dominated microbial assemblage was observed in the brine. These bacteria live under very high levels of reduced metals, ammonia, molecular hydrogen (H(2)), and dissolved organic carbon, as well as high concentrations of oxidized species of nitrogen (i.e., supersaturated nitrous oxide and ∼1 mmol⋅L(-1) nitrate) and sulfur (as sulfate). The existence of this system, with active biota, and a suite of reduced as well as oxidized compounds, is unusual given the millennial scale of its isolation from external sources of energy. The geochemistry of the brine suggests that abiotic brine-rock reactions may occur in this system and that the rich sources of dissolved electron acceptors prevent sulfate reduction and methanogenesis from being energetically favorable. The discovery of this ecosystem and the in situ biotic and abiotic processes occurring at low temperature provides a tractable system to study habitability of isolated terrestrial cryoenvironments (e.g., permafrost cryopegs and subglacial ecosystems), and is a potential analog for habitats on other icy worlds where water-rock reactions may cooccur with saline deposits and subsurface oceans.

Toward understanding life under subzero conditions: the significance of exploring psychrophilic "cold-shock" proteins.

Understanding the behavior of proteins under freezing conditions is vital for detecting and locating extraterrestrial life in cold environments, such as those found on Mars and the icy moons of Jupiter and Saturn. This review highlights the importance of studying psychrophilic "cold-shock" proteins, a topic that has yet to be explored. A strategy for analyzing the psychrophilic RNA helicase protein CsdA (Psyc_1082) from Psychrobacter arcticus 273-4 as a key protein for life under freezing temperatures is proposed. The experimental model presented here was developed based on previous data from investigations of Escherichia coli, P. arcticus 273-4, and RNA helicases. P. arcticus 273-4 is considered a model for life in freezing environments. It is capable of growing in temperatures as cold as -10°C by using physiological strategies to survive not only in freezing temperatures but also under low-water-activity and limited-nutrient-availability conditions. The analyses of its genome, transcriptome, and proteome revealed specific adaptations that allow it to inhabit freezing environments by adopting a slow metabolic strategy rather than a cellular dormancy state. During growth at subzero temperatures, P. arcticus 273-4 genes related to energy metabolism and carbon substrate incorporation are downregulated, and genes for maintenance of membranes, cell walls, and nucleic acid motion are upregulated. At -6°C, P. arcticus 273-4 does not upregulate the expression of either RNA or protein chaperones; however, it upregulates the expression of its cold-shock induced DEAD-box RNA helicase protein A (CsdA - Psyc_1082). CsdA - Psyc_1082 was investigated as a key helper protein for sustaining life in subzero conditions. Proving CsdA - Psyc_1082 to be functional as a key protein for life under freezing temperatures may extend the known minimum growth temperature of a mesophilic cell and provide key information about the mechanisms that underlie cold-induced biological systems in icy worlds.

New alk genes detected in Antarctic marine sediments.

Alkane monooxygenases (Alk) are the key enzymes for alkane degradation. In order to understand the dispersion and diversity of alk genes in Antarctic marine environments, this study analysed by clone libraries the presence and diversity of alk genes (alkB and alkM) in sediments from Admiralty Bay, King George Island, Peninsula Antarctica. The results show a differential distribution of alk genes between the sites, and the predominant presence of new alk genes, mainly in the pristine site. Sequences presented 53.10-69.60% nucleotide identity and 50.90-73.40% amino acid identity to alkB genes described in Silicibacter pomeroyi, Gordonia sp., Prauserella rugosa, Nocardioides sp., Rhodococcus sp., Nocardia farcinica, Pseudomonas putida, Acidisphaera sp., Alcanivorax borkumensis, and alkM described in Acinetobacter sp. This is the first time that the gene alkM was detected and described in Antarctic marine environments. The presence of a range of previously undescribed alk genes indicates the need for further studies in this environment.