Stratified response to environmental stress in a polar lichen characterized with FT-Raman microscopic analysis.

The role of Antarctic epilithic lichens in the primary colonization of rocks and in the formation of soils is receiving attention because of the production of the stress-protective biochemicals needed to combat radiation, desiccation and extremes of temperature. Raman microscopy has been used here to study the encrustations produced at the interface between the rock substratum and Buellia spp. lichen thalli; in addition to whewellite, calcium oxalate monohydrate, the presence of weddellite, the metastable dihydrate form, was confirmed in the encrustations. An unusual pigmentation of the rock surface found on detachment of the lichen growths is identified as beta-carotene from its characteristic Raman bands at 1525, 1191, 1157 and 1003 cm(-1); normally, beta-carotene, which has been identified as a UV-radiation protectant, is found at the exposed upper surface of the biological organism. The interface between the detached lichen thalli and the rock also contains whewellite as the sole biomineralization product--which suggests a possible strategy for the formulation of weddelite in the growing Buellia spp. colony as an anti-desiccant.

Non-destructive analysis of pigments and other organic compounds in lichens using Fourier-transform Raman spectroscopy: a study of Antarctic epilithic lichens.

Lichens in Antarctic habitats are subjected to environmental extremes, including UVB radiation, desiccation and low temperatures, as well as to rapid fluctuations in these. Lichens synthesise a variety of chemical compounds in response to their environmental conditions which contribute towards their colour, and which act as protectants against physiological stresses. The fluorescence generated by the lichens at 532 nm can be used in epifluorescence microscopy to identify their presence on substrata but this can severely affect the Raman spectra using visible excitation. The advantage of the near infrared excitation used in FT-Raman spectroscopy in minimising fluorescence emission facilitates the molecular characterisation of lichen encrustations without having to remove the thallus from its substrate or remove or otherwise damage any part of the thallus. Spectroscopic biomarkers are proposed which allow the lichens to be characterised by the identification of characteristic lichen substances; the use of these biomarkers for the preliminary taxonomic identification of Antarctic lichens is examined and some potential pitfalls are described.

Brines in seepage channels as eluants for subsurface relict biomolecules on Mars?

Water, vital for life, not only maintains the integrity of structural and metabolic biomolecules, it also transports them in solution or colloidal suspension. Any flow of water through a dormant or fossilized microbial community elutes molecules that are potentially recognizable as biomarkers. We hypothesize that the surface seepage channels emanating from crater walls and cliffs in Mars Orbiter Camera images results from fluvial erosion of the regolith as low-temperature hypersaline brines. We propose that, if such flows passed through extensive subsurface catchments containing buried and fossilized remains of microbial communities from the wet Hesperian period of early Mars (approximately 3.5 Ga ago), they would have eluted and concentrated relict biomolecules and delivered them to the surface. Life-supporting low-temperature hypersaline brines in Antarctic desert habitats provide a terrestrial analog for such a scenario. As in the Antarctic, salts would likely have accumulated in water-filled depressions on Mars by seasonal influx and evaporation. Liquid water in the Antarctic cold desert analogs occurs at -80 degrees C in the interstices of shallow hypersaline soils and at -50 degrees C in salt-saturated ponds. Similarly, hypersaline brines on Mars could have freezing points depressed below -50 degrees C. The presence of hypersaline brines on Mars would have extended the amount of time during which life might have evolved. Phototrophic communities are especially important for the search for life because the distinctive structures and longevity of their pigments make excellent biomarkers. The surface seepage channels are therefore not only of geomorphological significance, but also provide potential repositories for biomolecules that could be accessed by landers.

Aerobic endospore-forming bacteria from geothermal environments in northern Victoria Land, Antarctica, and Candlemas Island, South Sandwich archipelago, with the proposal of Bacillus fumarioli sp. nov.

Aerobic endospore-forming bacteria were isolated from soils taken from active fumaroles on Mount Rittmann and Mount Melbourne in northern Victoria Land, Antarctica, and from active and inactive fumaroles on Candlemas Island, South Sandwich archipelago. The Mt Rittmann and Mt Melbourne soils yielded a dominant, moderately thermophilic and acidophilic, aerobic endospore-former growing at pH 5.5 and 50 degrees C, and further strains of the same organism were isolated from a cold, dead fumarole at Clinker Gulch, Candlemas Island. Amplified rDNA restriction analysis, SDS-PAGE and routine phenotypic tests show that the Candlemas Island isolates are not distinguishable from the Mt Rittmann strains, although the two sites are 5600 km apart, and 16S rDNA sequence comparisons and DNA relatedness data support the proposal of a new species, Bacillus fumarioli, the type strain of which is LMG 17489T.

Vibrational raman spectroscopic study of scytonemin, the UV-protective cyanobacterial pigment.

The Raman spectrum of the photoprotective pigment scytonemin found in cyanobacterial sheaths has been obtained for the first time. Its skeletal structure is extensively conjugated and unique in nature. Detailed molecular vibrational assignments are proposed and a distinctive group of four corroborative vibrational bands have been identified as unique indicators for the compound. These bands, especially a prominent feature at wavenumber 1590 cm(-1), are sufficiently conspicuous to be detectable in the mixed biomolecular pools of undisturbed natural microbial communities. This has been confirmed by demonstrating the Raman spectral bands for scytonemin in a sample of an intact intertidal cyanobacterial mat.

Investigations into an unknown organism on the martian meteorite Allan Hills 84001.

Examination of fracture surfaces near the fusion crust of the martian meteorite Allan Hills (ALH) 84001 have been conducted using scanning electron microscopy (SEM) and atomic force microscopy (AFM) and has revealed structures strongly resembling mycelium. These structures were compared with similar structures found in Antarctic cryptoendolithic communities. On morphology alone, we conclude that these features are not only terrestrial in origin but probably belong to a member of the Actinomycetales, which we consider was introduced during the Antarctic residency of this meteorite. If true, this is the first documented account of terrestrial microbial activity within a meteorite from the Antarctic blue ice fields. These structures, however, do not bear any resemblance to those postulated to be martian biota, although they are a probable source of the organic contaminants previously reported in this meteorite.

The state and future of Mars polar science and exploration.

As the planet's principal cold traps, the martian polar regions have accumulated extensive mantles of ice and dust that cover individual areas of approximately 10(6) km2 and total as much as 3-4 km thick. From the scarcity of superposed craters on their surface, these layered deposits are thought to be comparatively young--preserving a record of the seasonal and climatic cycling of atmospheric CO2, H2O, and dust over the past approximately 10(5)-10(8) years. For this reason, the martian polar deposits may serve as a Rosetta Stone for understanding the geologic and climatic history of the planet--documenting variations in insolation (due to quasiperiodic oscillations in the planet's obliquity and orbital elements), volatile mass balance, atmospheric composition, dust storm activity, volcanic eruptions, large impacts, catastrophic floods, solar luminosity, supernovae, and perhaps even a record of microbial life. Beyond their scientific value, the polar regions may soon prove important for another reason--providing a valuable and accessible reservoir of water to support the long-term human exploration of Mars. In this paper we assess the current state of Mars polar research, identify the key questions that motivate the exploration of the polar regions, discuss the extent to which current missions will address these questions, and speculate about what additional capabilities and investigations may be required to address the issues that remain outstanding.

Response of pioneer soil microalgal colonists to environmental change in Antarctica.

There is increasing evidence of climate change in Antarctica, especially elevated temperature and ultraviolet B (UVB) flux within the ozone "hole." Its origins are debatable, but the effects on ice recession, water availability, and summer growth conditions are demonstrable. Light-dependent, temperature-sensitive, fast-growing organisms respond to these physical and biogeographical changes. Microalgae (cyanobacteria and eukaryotic algae), which are pioneer colonists of Antarctic mineral fellfield soils, are therefore highly suitable biological indicators of such changes. In frost-heaved soil polygons containing naturally sorted fine mineral particles, microalgal growth is restricted to a shallow zone of light penetration. By virtue of this light requirement, microalgae are exposed to extreme seasonal fluctuations in temperature (air and black-body radiation), photosynthetically active radiation, UV radiation, and desiccation. Dominance of conspicuous autofluorescent indicator species with distinctive morphology allowed quantification of responses using epifluorescence microscopy, and image analysis of undisturbed, unstained communities. However, the physical changes in climate, although significant in the long term, are gradual. The changes were therefore amplified experimentally by enclosing the communities at a fellfield site on Signy Island, maritime Antarctica, in cloches (small greenhouses). These were made of polystyrene of either UV transparent or UV opaque acrylic plastic, with or without walls. During a 6-year period, statistically significant changes were observed in microalgal colonization of the soil surface and in the morphology of filamentous populations. Evidence of community succession correlated with measured changes in local environment was found. Results from Signy Island and at continental sites on Alexander Island suggested that rates of microalgal colonization and community development might change significantly during current climate changes in Antarctica.