Search

It is generally accepted that bacterial diversity in a community confers resistance to environmental perturbation. Communities with high bacterial diversity are less likely to be impacted by environmental changes such as warming. As such, hydrocarbon-contaminated Antarctic soil that are typically characterised by low bacterial diversity and highly selective taxonomic composition are expected to be more sensitive to changes in temperature than uncontaminated Antarctic soil. To test this hypothesis, we evaluated the response of bacterial community structure to warming of hydrocarbon-contaminated and uncontaminated soil collected from Casey Station, Windmill Island, East Antarctica by using microcosms incubated at 5, 10 and 15 °C over a period of 12 weeks. Our results showed that shifts occurred in the bacterial community in relation to the incubation temperatures in both the hydrocarbon-contaminated and uncontaminated soil, with a stronger response observed in the contaminated soil. Taxa referred as comprising hydrocarbon-degrading genera such as Rhodococcus, was the most prevalent genus in the contaminated soil after incubation at 15 °C, accounting for approximately 32–50% of the total detected genera. However, there were no significant differences in the selected functional genes, potentially suggesting high levels of metabolic plasticity in the studied soil bacterial communities. Overall, we showed that hydrocarbon contamination in soil might lead to lower bacterial community stability against environmental perturbation such as temperature variation.

Despite an increasing number of Antarctic soil diversity assessments, understanding of the bacterial community composition in the arid soil environments of the maritime/continental Antarctic transitional zone remains lacking. Most documented microbiological studies had focused on either the wetter environments of the Antarctic Peninsula/Scotia arc or the exceptionally arid deserts of the Dry Valleys of continental Antarctica. In this study, soil bacterial diversity from three relatively arid sites on Alexander Island and the physicochemical parameters that might influence it were assessed. In general, the study sites exhibited levels of pH, hydration and metal content different from previous reports of maritime or continental Antarctic soil habitats. Although the soil from Alexander Island exhibited similar phylum-level bacterial taxonomic composition to those of other cold and arid environments, each study site was found to harbour significantly different bacterial assemblages. The latter finding was supported by three complementary molecular methods selected to address different elements of diversity. Our analyses of the measured parameters suggest that the differences in bacterial communities were best explained by soil pH and copper content. Using these data, we suggest that soil pH might play an important role in structuring bacterial assemblage patterns across polar soils.

Soil bacterial diversity at environmentally distinct locations on Signy Island, South Orkney Islands was examined using the denaturing gradient gel profiling approach. A range of chemical variables in soils at each site was determined in order to describe variation between locations. No apparent differences in Shannon Diversity Index (H′) were observed. However, as revealed in an analysis of similarity (ANOSIM), the dominant bacterial communities of all eight studied locations were significantly different. Within this, higher levels of similarity were observed between penguin rookeries, seal wallows and vegetated soils, all of which share varying levels of impact from vertebrate activity, in contrast with more barren soil. In addition, the lowest H′ value was detected from the latter soil which also has the most extreme environmental conditions, and its bacterial community has the greatest genetic distance from the other locations. DGGE analyses indicated that the majority of the excised and sequenced bands were attributable to the Bacteroidetes. Across a range of ten environmental variables, multivariate correlation analysis suggested that a combination of pH, conductivity, copper and lead content potentially contributed explanatory value to the measured soil bacterial diversity.

Bacterial community structures in soils collected from eight sites around Casey Station, Antarctica, were investigated using denaturing gradient gel electrophoresis (DGGE) of amplified 16S rRNA gene fragments. Higher bacterial diversity was found in soils from protected or relatively low human-impacted sites in comparison to highly impacted sites. However, the highest diversity was detected in samples from Wilkes Tip, a former waste disposal site that has been undisturbed for the last 50 years. Comparison of community structure based on non-metric multidimensional scaling plots revealed that all sites, except the hydrocarbon-contaminated (oil spill) site, were clustered with a 45% similarity. A total of 23 partial 16S rRNA gene sequences were obtained from the excised DGGE bands, with the majority of the sequences closely related to those of the Cytophaga–Flexibacter–Bacteroides group. No significant correlation was established between environmental variables, including soil pH, electrical conductivity, carbon, nitrogen, water content and heavy metals, with bacterial diversity across the eight study sites.