No abstract

Viable prokaryotes have been detected in basal sediments beneath the few Northern Hemisphere glaciers that have been sampled for microbial communities. However, parallel studies have not previously been conducted in the Southern Hemisphere, and subglacial environments in general are a new and underexplored niche for microbes. Unfrozen subglacial sediments and overlying glacier ice samples collected aseptically from the Fox Glacier and Franz Josef Glacier in the Southern Alps of New Zealand now have been shown to harbor viable microbial populations. Total direct counts of 2-7 x 10(6) cells g(-1) dry weight sediment were observed, whereas culturable aerobic heterotrophs ranged from 6-9 x 10(5) colony-forming units g(-1) dry weight. Viable counts in the glacier ice typically were 3-4 orders of magnitude smaller than in sediment. Nitrate-reducing and ferric iron-reducing bacteria were detected in sediment samples from both glaciers, but were few or below detection limits in the ice samples. Nitrogen-fixing bacteria were detected only in the Fox Glacier sediment. Restriction fragment analysis of 16S rDNA amplified from 37 pure cultures of aerobic heterotrophs capable of growth at 4 degrees C yielded 23 distinct groups, of which 11 were identified as beta-Proteobacteria. 16S rDNA sequences from representatives of these 11 groups were analyzed phylogenetically and shown to cluster with bacteria such as Polaromonas vacuolata and Rhodoferax antarcticus, or with clones obtained from permanently cold environments. Chemical analysis of sediment and ice samples revealed a dilute environment for microbial life. Nevertheless, both the sediment samples and one ice sample demonstrated substantial aerobic mineralization of 14C-acetate at 8 degrees C, indicating that sufficient nutrients and viable psychrotolerant microbes were present to support metabolism. Unfrozen subglacial sediments may represent a significant global reservoir of biological activity with the potential to influence glacier meltwater chemistry.

Data from six sites in Victoria Land (72-77ºS) investigating co-variation in soil communities (microbial and invertebrate) with biogeochemical properties showthe influence of soil properties on habitat suitability varied among local landscapes as well as across climate gradients. Species richness of metazoan invertebrates (Nematoda, Tardigrada and Rotifera) was similar to previous descriptions in this region, though identification of three cryptic nematode species of Eudorylaimus through DNA analysis contributed to the understanding of controls over habitat preferences for individual species. Denaturing Gradient Gel Electrophoresis profiles revealed unexpectedly high diversity of bacteria. Distribution of distinct bacterial communities was associated with specific sites in northern and southern Victoria Land, as was the distribution of nematode and tardigrade species. Variation in soil metazoan communities was related to differences in soil organic matter, while bacterial diversity and community structure were not strongly correlated with any single soil property. There were no apparent correlations between metazoan and bacterial diversity, suggesting that controls over distribution and habitat suitability are different for bacterial and metazoan communities. Our results imply that top-down controls over bacterial diversity mediated by their metazoan consumers are not significant determinants of bacterial community structure and biomass in these ecosystems.

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Antarctic exploration and research have led to some significant although localized impacts on the environment. Human impacts occur around current or past scientific research stations, typically located on ice-free areas that are predominantly soils. Fuel spills, the most common occurrence, have the potential to cause the greatest environmental impact in the Antarctic through accumulation of aliphatic and aromatic compounds. Effective management of hydrocarbon spills is dependent on understanding how they impact soil properties such as moisture, hydrophobicity, soil temperature, and microbial activity. Numbers of hydrocarbon-degrading bacteria, typically Rhodococcus, Sphingomonas, and Pseudomonas species for example, may become elevated in contaminated soils, but overall microbial diversity declines. Alternative management practices to the current approach of "dig it up and ship it out" are required but must be based on sound information. This review summarizes current understanding of the extent and effects of hydrocarbon spillage on Antarctic soils; the observed physical, chemical, and biological responses of such soils; and current gaps in knowledge.

A combination of culture-independent and culturing methods was used to determine the impacts of hydrocarbon contamination on the diversity of bacterial communities in coastal soil from Ross Island, Antarctica. While numbers of culturable aerobic heterotrophic microbes were 1-2 orders of magnitude higher in the hydrocarbon-contaminated soil than control soil, the populations were less diverse. Members of the divisions Fibrobacter/Acidobacterium, Cytophaga/Flavobacterium/Bacteroides, Deinococcus/Thermus, and Low G+C gram positive occurred almost exclusively in control soils whereas the contaminated soils were dominated by Proteobacteria; specifically, members of the genera Pseudomonas, Sphingomonas and Variovorax, some of which degrade hydrocarbons. Members of the Actinobacteria were found in both soils.

Bioremediation is increasingly viewed as an appropriate remediation technology for hydrocarbon-contaminated polar soils. As for all soils, the successful application of bioremediation depends on appropriate biodegradative microbes and environmental conditions in situ. Laboratory studies have confirmed that hydrocarbon-degrading bacteria typically assigned to the genera Rhodococcus, Sphingomonas or Pseudomonas are present in contaminated polar soils. However, as indicated by the persistence of spilled hydrocarbons, environmental conditions in situ are suboptimal for biodegradation in polar soils. Therefore, it is likely that ex situ bioremediation will be the method of choice for ameliorating and controlling the factors limiting microbial activity, i.e. low and fluctuating soil temperatures, low levels of nutrients, and possible alkalinity and low moisture. Care must be taken when adding nutrients to the coarse-textured, low-moisture soils prevalent in continental Antarctica and the high Arctic because excess levels can inhibit hydrocarbon biodegradation by decreasing soil water potentials. Bioremediation experiments conducted on site in the Arctic indicate that land farming and biopiles may be useful approaches for bioremediation of polar soils.

Microbial degradation of DDT residues is one mechanism for loss of DDT from soil. In this review pathways for biodegradation of DDT, DDD, and DDE by bacteria and fungi are described. Biodegradation of DDT residues can proceed in soil, albeit at a slow rate. To enhance degradation in situ a number of strategies are proposed. They include the addition of DDT-metabolising microbes to contaminated soils and/or the manipulation of environmental conditions to enhance the activity of these microbes. Ligninolytic fungi and chlorobiphenyl degrading bacteria are promising candidates for remediation. Flooding of soil and the addition of organic matter can enhance DDT degradation. As biodegradation may be inhibited by lack of access of the microbe to the contaminant, the soil may need to be pre-treated with a surfactant. Unlike DDT, little is known about the biodegradation of DDE, and this knowledge is crucial as DDE can be the predominant residue in some soils.