Planococcus halocryophilus strain Or1, isolated from high Arctic permafrost, grows and divides at À 15 1C, the lowest temperature demonstrated to date, and is metabolically active at À 25 1C in frozen permafrost microcosms. To understand how P. halocryophilus Or1 remains active under the subzero and osmotically dynamic conditions that characterize its native permafrost habitat, we investigated the genome, cell physiology and transcriptomes of growth at À 15 1C and 18% NaCl compared with optimal (25 1C) temperatures. Subzero growth coincides with unusual cell envelope features of encrustations surrounding cells, while the cytoplasmic membrane is significantly remodeled favouring a higher ratio of saturated to branched fatty acids. Analyses of the 3.4 Mbp genome revealed that a suite of cold and osmotic-specific adaptive mechanisms are present as well as an amino acid distribution favouring increased flexibility of proteins. Genomic redundancy within 17% of the genome could enable P. halocryophilus Or1 to exploit isozyme exchange to maintain growth under stress, including multiple copies of osmolyte uptake genes (Opu and Pro genes). Isozyme exchange was observed between the transcriptome data sets, with selective upregulation of multi-copy genes involved in cell division, fatty acid synthesis, solute binding, oxidative stress response and transcriptional regulation. The combination of protein flexibility, resource efficiency, genomic plasticity and synergistic adaptation likely compensate against osmotic and cold stresses. These results suggest that non-spore forming P. halocryophilus Or1 is specifically suited for active growth in its Arctic permafrost habitat (ambient temp. B À 16 1C), indicating that such cryoenvironments harbor a more active microbial ecosystem than previously thought.

A committee of the Mars Exploration Program Analysis Group (MEPAG) has reviewed and updated the description of Special Regions on Mars as places where terrestrial organisms might replicate (per the COSPAR Planetary Protection Policy). This review and update was conducted by an international team (SR-SAG2) drawn from both the biological science and Mars exploration communities, focused on understanding when and where Special Regions could occur. The study applied recently available data about martian environments and about terrestrial organisms, building on a previous analysis of Mars Special Regions (2006) undertaken by a similar team. Since then, a new body of highly relevant information has been generated from the Mars Reconnaissance Orbiter (launched in 2005) and Phoenix (2007) and data from Mars Express and the twin Mars Exploration Rovers (all 2003). Results have also been gleaned from the Mars Science Laboratory (launched in 2011). In addition to Mars data, there is a considerable body of new data regarding the known environmental limits to life on Earth-including the potential for terrestrial microbial life to survive and replicate under martian environmental conditions. The SR-SAG2 analysis has included an examination of new Mars models relevant to natural environmental variation in water activity and temperature; a review and reconsideration of the current parameters used to define Special Regions; and updated maps and descriptions of the martian environments recommended for treatment as "Uncertain" or "Special" as natural features or those potentially formed by the influence of future landed spacecraft. Significant changes in our knowledge of the capabilities of terrestrial organisms and the existence of possibly habitable martian environments have led to a new appreciation of where Mars Special Regions may be identified and protected. The SR-SAG also considered the impact of Special Regions on potential future human missions to Mars, both as locations of potential resources and as places that should not be inadvertently contaminated by human activity.

No abstract

Methane (CH 4 ) emission by carbon-rich cryosols at the high latitudes in Northern Hemisphere has been studied extensively. In contrast, data on the CH 4 emission potential of carbon-poor cryosols is limited, despite their spatial predominance. This work employs CH 4 flux measurements in the field and under laboratory conditions to show that the mineral cryosols at Axel Heiberg Island in the Canadian high Arctic consistently consume atmospheric CH 4 . Omics analyses present the first molecular evidence of active atmospheric CH 4 -oxidizing bacteria (atmMOB) in permafrost-affected cryosols, with the prevalent atmMOB genotype in our acidic mineral cryosols being closely related to Upland Soil Cluster α. The atmospheric (atm) CH 4 uptake at the study site increases with ground temperature between 0°C and 18°C. Consequently, the atm CH 4 sink strength is predicted to increase by a factor of 5-30 as the Arctic warms by 5-15°C over a century. We demonstrate that acidic mineral cryosols are a previously unrecognized potential of CH 4 sink that requires further investigation to determine its potential impact on larger scales. This study also calls attention to the poleward distribution of atmMOB, as well as to the potential influence of microbial atm CH 4 oxidation, in the context of regional CH 4 flux models and global warming.

This paper documents perennial spring activity at Expedition Fiord on western Axel Heiberg Island in the Canadian High Arctic. Two groups of mineralized springs occur near the McGill University Axel Heiberg Research Station located at 79°26'N, 90°46'W. The first is at Gypsum Hill, 3 km from the terminus of the White and Thompson glaciers, and the second site is at Colour Peak, approximately 10 km downvalley near the head of Expedition Fiord. Each spring group consists of 20-40 vents spread over several hundred square metres. The highly mineralized nature of the discharge causes a freezing-point depression of 7-10°C and produces a range of precipitates and travertine deposits. Year-round water temperature and discharge rate measurements have been obtained, demonstrating perennial activity at these sites. Results indicate that temperatures range from -4.0 to 6.6°C among the individual sources; however, water temperatures at the various outlets remain constant throughout the year despite a mean annual air temperature of -15°C. Although discharge from any one outlet is low (<0.5 to 2.0 L/s), the total discharge is substantial, each year producing several seasonal frost mounds and an icing 180 000 - 300 000 m2 at the Gypsum Hill site.

Microbialite-forming communities interact with the environment and influence the precipitation of calcium carbonate through their metabolic activity. The functional genes associated with these metabolic processes and their environmental interactions are therefore critical to microbialite formation. The microbiomes associated with microbialite-forming ecosystems are just now being elucidated and the extent of shared pathways and taxa across different environments is not fully known. In this study, we profiled the microbiome of microbial communities associated with lacustrine thrombolites located in Lake Clifton, Western Australia using metagenomic sequencing and compared it to the non-lithifying mats associated with surrounding sediments to determine whether differences in the mat microbiomes, particularly with respect to metabolic pathways and environmental interactions, may potentially contribute to thrombolite formation. Additionally, we used stable isotope biosignatures to delineate the dominant metabolism associated with calcium carbonate precipitation in the thrombolite build-ups. Results indicated that the microbial community associated with the Lake Clifton thrombolites was predominantly bacterial (98.4%) with Proteobacteria, Cyanobacteria, Bacteroidetes, and Actinobacteria comprising the majority of annotated reads. Thrombolite-associated mats were enriched in photoautotrophic taxa and functional genes associated with photosynthesis. Observed δ13C values of thrombolite CaCO3 were enriched by at least 3.5‰ compared to theoretical values in equilibrium with lake water DIC, which is consistent with the occurrence of photoautotrophic activity in thrombolite-associated microbial mats. In contrast, the microbiomes of microbial communities found on the sandy non-lithifying sediments of Lake Clifton represented distinct microbial communities that varied in taxa and functional capability and were enriched in heterotrophic taxa compared to the thrombolite-associated mats. This study provides new insight into the taxa and functional capabilities that differentiate potentially lithifying mats from other non-lithifying types and suggests that thrombolites are actively accreting and growing in limited areas of Lake Clifton.

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Studies of microbial biogeography are often convoluted by extremely high diversity and differences in microenvironmental factors such as pH and nutrient availability. Desert endolithic (inside rock) communities are relatively simple ecosystems that can serve as a tractable model for investigating long-range biogeographic effects on microbial communities. We conducted a comprehensive survey of endolithic sandstones using high-throughput marker gene sequencing to characterize global patterns of diversity in endolithic microbial communities. We also tested a range of abiotic variables in order to investigate the factors that drive community assembly at various trophic levels. Macroclimate was found to be the primary driver of endolithic community composition, with the most striking difference witnessed between hot and polar deserts. This difference was largely attributable to the specialization of prokaryotic and eukaryotic primary producers to different climate conditions. On a regional scale, microclimate and properties of the rock substrate were found to influence community assembly, although to a lesser degree than global hot versus polar conditions. We found new evidence that the factors driving endolithic community assembly differ between trophic levels. While phototrophic taxa, mostly oxygenic photosynthesizers, were rigorously selected for among different sites, heterotrophic taxa were more cosmopolitan, suggesting that stochasticity plays a larger role in heterotroph assembly. This study is the first to uncover the global drivers of desert endolithic diversity using high-throughput sequencing. We demonstrate that phototrophs and heterotrophs in the endolithic community assemble under different stochastic and deterministic influences, emphasizing the need for studies of microorganisms in context of their functional niche in the community.