Some like it cold: understanding the survival strategies of psychrophiles.

Much of the Earth's surface, both marine and terrestrial, is either periodically or permanently cold. Although habitats that are largely or continuously frozen are generally considered to be inhospitable to life, psychrophilic organisms have managed to survive in these environments. This is attributed to their innate adaptive capacity to cope with cold and its associated stresses. Here, we review the various environmental, physiological and molecular adaptations that psychrophilic microorganisms use to thrive under adverse conditions. We also discuss the impact of modern "omic" technologies in developing an improved understanding of these adaptations, highlighting recent work in this growing field.

Accuracy assessment of land surface temperature retrievals from Landsat 7 ETM + in the Dry Valleys of Antarctica using iButton temperature loggers and weather station data.

The McMurdo Dry Valleys of Antarctica are the largest snow/ice-free regions on this vast continent, comprising 1% of the land mass. Due to harsh environmental conditions, the valleys are bereft of any vegetation. Land surface temperature is a key determinate of microclimate and a driver for sensible and latent heat fluxes of the surface. The Dry Valleys have been the focus of ecological studies as they arguably provide the simplest trophic structure suitable for modelling. In this paper, we employ a validation method for land surface temperatures obtained from Landsat 7 ETM + imagery and compared with in situ land surface temperature data collected from four transects totalling 45 iButtons. A single meteorological station was used to obtain a better understanding of daily and seasonal cycles in land surface temperatures. Results show a good agreement between the iButton and the Landsat 7 ETM + product for clear sky cases. We conclude that Landsat 7 ETM + derived land surface temperatures can be used at broad spatial scales for ecological and meteorological research.

Unexpected Delayed Incursion of Highly Pathogenic Avian Influenza H5N1 (Clade 2.3.4.4b) Into the Antarctic Region.

The current highly pathogenic avian influenza H5N1 panzootic is having substantial impacts on wild birds and marine mammals. Following major and widespread outbreaks in South America, an incursion to Antarctica occurred late in the austral summer of 2023/2024 and was confined to the region of the Antarctic Peninsula. To infer potential underlying processes, we compiled H5N1 surveillance data from Antarctica and sub-Antarctic Islands prior to the first confirmed cases.

Genome sequence of temperate bacteriophage Psymv2 from Antarctic Dry Valley soil isolate Psychrobacter sp. MV2.

A temperate phage, Psymv2, was isolated from an Antarctic soil bacterium, Psychrobacter sp. MV2. The morphology of Psymv2 was typical of the Siphoviridae, with an isometric head and non-contractile tail. The Psymv2 genome was found to be 35,725 bp in length, had a G + C content of 44.5 %, with 49 protein-coding genes and one tRNA gene predicted. Integration of Psymv2 occurred at an ssrA gene, with the last 27 bases of this gene directly repeated at the prophage ends. The genome was organised in a modular fashion: integration, regulation, packaging, head assembly, tail assembly, host specificity and lysis. While the genome sequence had little similarity on a nucleotide level to previously reported phage sequences, the genome architecture resembled that of Siphoviridae of low G + C Gram-positive bacteria. The closest relatives to Psymv2 were uncharacterized putative prophages within the P. arcticus 273-4 and Acinetobacter baumannii 6013113 genomes. Global alignment of the Psymv2 genome and these prophages revealed significant conservation of the structural modules despite the large spatial divergence of their hosts. A number of unique ORFs were identified in the Psymv2 genome that may contribute to phage and lysogen fitness.

Microbial Succession under Freeze-Thaw Events and Its Potential for Hydrocarbon Degradation in Nutrient-Amended Antarctic Soil.

The polar regions have relatively low richness and diversity of plants and animals, and the basis of the entire ecological chain is supported by microbial diversity. In these regions, understanding the microbial response against environmental factors and anthropogenic disturbances is essential to understand patterns better, prevent isolated events, and apply biotechnology strategies. The Antarctic continent has been increasingly affected by anthropogenic contamination, and its constant temperature fluctuations limit the application of clean recovery strategies, such as bioremediation. We evaluated the bacterial response in oil-contaminated soil through a nutrient-amended microcosm experiment using two temperature regimes: (i) 4 °C and (ii) a freeze-thaw cycle (FTC) alternating between -20 and 4 °C. Bacterial taxa, such as Myxococcales, Chitinophagaceae, and Acidimicrobiales, were strongly related to the FTC. Rhodococcus was positively related to contaminated soils and further stimulated under FTC conditions. Additionally, the nutrient-amended treatment under the FTC regime enhanced bacterial groups with known biodegradation potential and was efficient in removing hydrocarbons of diesel oil. The experimental design, rates of bacterial succession, and level of hydrocarbon transformation can be considered as a baseline for further studies aimed at improving bioremediation strategies in environments affected by FTC regimes.

First report of homoanatoxin-a and associated dog neurotoxicosis in New Zealand.

In November 2005, at least five dogs died rapidly after contact with water from the Hutt River (lower North Island, New Zealand). Necropsy performed 24h later on one of the dogs (a 20-month-old Labrador) revealed few findings of interest, except for copious amounts of froth in the respiratory tract down to the bifurcation of the trachea and large quantities of algal material in the dog's stomach. Low and relatively stable flows in the Hutt River during spring had resulted in the proliferation of benthic cyanobacteria that formed large black/brown mats along the river edge. Samples from the Labrador's stomach contents and cyanobacterial mats were analysed microscopically and screened using chemical and biochemical assays for cyanotoxins: anatoxin-a, homoanatoxin-a, cylindrospermopsins, saxitoxins and microcystins. Liquid chromatography-mass spectrometry (LC-MS) confirmed the presence of the neurotoxic cyanotoxins anatoxin-a and homoanatoxin-a and their degradation products, dihydro-anatoxin-a and dihydro-homoanatoxin-a. This is the first report of homoanatoxin-a and associated degradation product in New Zealand. Based on morphology, the causative species was identified as Phormidium sp. Subsequent phylogenetic analysis of 16S rRNA gene sequences demonstrated that the causative organism was most similar to Phormidium autumnale. Further investigations led to the detection of homoanatoxin-a and anatoxin-a in cyanobacterial mats from four other rivers in the Wellington region (lower North Island, New Zealand). Access restrictions were placed on over 60% of river catchments in the western Wellington region, severely affecting recreational users.

Aerobiology Over Antarctica - A New Initiative for Atmospheric Ecology.

The role of aerial dispersal in shaping patterns of biodiversity remains poorly understood, mainly due to a lack of coordinated efforts in gathering data at appropriate temporal and spatial scales. It has been long known that the rate of dispersal to an ecosystem can significantly influence ecosystem dynamics, and that aerial transport has been identified as an important source of biological input to remote locations. With the considerable effort devoted in recent decades to understanding atmospheric circulation in the south-polar region, a unique opportunity has emerged to investigate the atmospheric ecology of Antarctica, from regional to continental scales. This concept note identifies key questions in Antarctic microbial biogeography and the need for standardized sampling and analysis protocols to address such questions. A consortium of polar aerobiologists is established to bring together researchers with a common interest in the airborne dispersion of microbes and other propagules in the Antarctic, with opportunities for comparative studies in the Arctic.

Benthic microbial communities of coastal terrestrial and ice shelf Antarctic meltwater ponds.

The numerous perennial meltwater ponds distributed throughout Antarctica represent diverse and productive ecosystems central to the ecological functioning of the surrounding ultra oligotrophic environment. The dominant taxa in the pond benthic communities have been well described however, little is known regarding their regional dispersal and local drivers to community structure. The benthic microbial communities of 12 meltwater ponds in the McMurdo Sound of Antarctica were investigated to examine variation between pond microbial communities and their biogeography. Geochemically comparable but geomorphologically distinct ponds were selected from Bratina Island (ice shelf) and Miers Valley (terrestrial) (<40 km between study sites), and community structure within ponds was compared using DNA fingerprinting and pyrosequencing of 16S rRNA gene amplicons. More than 85% of total sequence reads were shared between pooled benthic communities at different locations (OTU0.05), which in combination with favorable prevailing winds suggests aeolian regional distribution. Consistent with previous findings Proteobacteria and Bacteroidetes were the dominant phyla representing over 50% of total sequences; however, a large number of other phyla (21) were also detected in this ecosystem. Although dominant Bacteria were ubiquitous between ponds, site and local selection resulted in heterogeneous community structures and with more than 45% of diversity being pond specific. Potassium was identified as the most significant contributing factor to the cosmopolitan community structure and aluminum to the location unique community based on a BEST analysis (Spearman's correlation coefficient of 0.632 and 0.806, respectively). These results indicate that the microbial communities in meltwater ponds are easily dispersed regionally and that the local geochemical environment drives the ponds community structure.

Abiotic factors influence microbial diversity in permanently cold soil horizons of a maritime-associated Antarctic Dry Valley.

The McMurdo Dry Valleys collectively comprise the most extensive ice-free region in Antarctica and are considered one of the coldest arid environments on Earth. In low-altitude maritime-associated valleys, mineral soil profiles show distinct horizontal structuring, with a surface arid zone overlying a moist and biologically active zone generated by seasonally melted permafrost. In this study, long-term microenvironmental monitoring data show that temperature and soil humidity regimes vary in the soil horizons of north- and south-facing slopes within the Miers Valley, a maritime valley in the McMurdo Dry Valleys. We found that soil bacterial communities varied from the north to the south. The microbial assemblages at the surface and shallow subsurface depths displayed higher metabolic activity and diversity compared to the permafrost soil interface. Multivariate analysis indicated that K, C, Ca and moisture influenced the distribution and structure of microbial populations. Furthermore, because of the large % RH gradient between the frozen subsurface and the soil surface we propose that water transported to the surface as water vapour is available to microbial populations, either as a result of condensation processes or by direct adsorption from the vapour phase.

Molecular adaptations to psychrophily: the impact of 'omic' technologies.

The ability of cold-adapted microorganisms (generally referred to as psychrophiles) to survive is the result of molecular evolution and adaptations which, together, counteract the potentially deleterious effects of low kinetic energy environments and the freezing of water. These physiological adaptations are seen at many levels. Against a background of detailed comparative protein structural analyses, the recent surge of psychrophile proteome, genome, metagenome and transcriptome sequence data has triggered a series of sophisticated analyses of changes in global protein composition. These studies have revealed consistent and statistically robust changes in amino acid composition, interpreted as evolutionary mechanisms designed to destabilise protein structures, as well as identifying the presence of novel genes involved in cold adaptation.

Bacterial diversity in three different Antarctic Cold Desert mineral soils.

A bacterial phylogenetic survey of three environmentally distinct Antarctic Dry Valley soil biotopes showed a high proportion of so-called "uncultured" phylotypes, with a relatively low diversity of identifiable phylotypes. Cyanobacterial phylotypic signals were restricted to the high-altitude sample, whereas many of the identifiable phylotypes, such as the members of the Actinobacteria, were found at all sample sites. Although the presence of Cyanobacteria and Actinobacteria is consistent with previous culture-dependent studies of microbial diversity in Antarctic Dry Valley mineral soils, many phylotypes identified by 16S rDNA analysis were of groups that have not hitherto been cultured from Antarctic soils. The general belief that such "extreme" environments harbor a relatively low species diversity was supported by the calculation of diversity indices. The detection of a substantial number of uncultured bacterial phylotypes showing low BLAST identities (< 95%) suggests that Antarctic Dry Valley mineral soils harbor a pool of novel psychrotrophic taxa.

Design of 16S rRNA-targeted oligonucleotide probes for detecting cultured and uncultured archaeal lineages in high-temperature environments.

In order to facilitate the evaluation of archaeal community diversity and distribution in high-temperature environments, 14 16S rRNA oligonucleotide probes were designed. Adequate hybridization and wash conditions of the probes encompassing most known hyperthermophilic Archaea, members of the orders Thermococcales, Desulfurococcales and Sulfolobales, of the families Methanocaldococcaceae, Pyrodictiaceae and Thermoproteaceae, of the genera Archaeoglobus, Methanopyrus and Ignicoccus, and of the as yet uncultured lineages Korarchaeota, Crenarchaeota marine group I, deep-sea hydrothermal vent euryarchaeotic group 2 (DHVE 2), and deep-sea hydrothermal vent euryarchaeotic group 8 (DHVE 8) were determined by dot-blot hybridization from target and non-target reference organisms and environmental clones. The oligonucleotide probes were also used to evaluate the archaeal community composition in nine deep-sea hydrothermal vent samples. All probes, except those targeting members of Sulfolobales, Thermoproteaceae, Pyrodictiaceae and Korarchaeota, gave positive hybridization signals when hybridized against 16S rDNA amplification products obtained from hydrothermal DNA extracts. The results confirmed the widespread occurrence of Thermococcales, Desulfurococcales, Methanocaldococcaceae and Archaeoglobus in deep-sea hydrothermal vents, and extended the known ecological habitats of uncultured lineages. Despite their wide coverage, the probes were unable to resolve the archaeal communities associated with hydrothermally influenced sediments, suggesting that these samples may contain novel lineages. This suite of oligonucleotide probes may represent an efficient tool for rapid qualitative and quantitative characterization of archaeal communities. Their application would help to provide new insights in the future into the composition, distribution and abundance of Archaea in high-temperature environments.