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Abstract BackgroundAntarctica and its unique biodiversity are increasingly at risk from the effects of global climate change and other human influences. A significant recent element underpinning strategies for Antarctic conservation has been the development of a system of Antarctic Conservation Biogeographic Regions (ACBRs). The datasets supporting this classification are, however, dominated by eukaryotic taxa, with contributions from the bacterial domain restricted to Actinomycetota and Cyanobacteriota. Nevertheless, the ice-free areas of the Antarctic continent and the sub-Antarctic islands are dominated in terms of diversity by bacteria. Our study aims to generate a comprehensive phylogenetic dataset of Antarctic bacteria with wide geographical coverage on the continent and sub-Antarctic islands, to investigate whether bacterial diversity and distribution is reflected in the current ACBRs. ResultsSoil bacterial diversity and community composition did not fully conform with the ACBR classification. Although 19% of the variability was explained by this classification, the largest differences in bacterial community composition were between the broader continental and maritime Antarctic regions, where a degree of structural overlapping within continental and maritime bacterial communities was apparent, not fully reflecting the division into separate ACBRs. Strong divergence in soil bacterial community composition was also apparent between the Antarctic/sub-Antarctic islands and the Antarctic mainland. Bacterial communities were partially shaped by bioclimatic conditions, with 28% of dominant genera showing habitat preferences connected to at least one of the bioclimatic variables included in our analyses. These genera were also reported as indicator taxa for the ACBRs. ConclusionsOverall, our data indicate that the current ACBR subdivision of the Antarctic continent does not fully reflect bacterial distribution and diversity in Antarctica. We observed considerable overlap in the structure of soil bacterial communities within the maritime Antarctic region and within the continental Antarctic region. Our results also suggest that bacterial communities might be impacted by regional climatic and other environmental changes. The dataset developed in this study provides a comprehensive baseline that will provide a valuable tool for biodiversity conservation efforts on the continent. Further studies are clearly required, and we emphasize the need for more extensive campaigns to systematically sample and characterize Antarctic and sub-Antarctic soil microbial communities. 

Abstract Antarctic soils are unique from those found nearly anywhere else on Earth yet can still harbor a broad diversity of microorganisms able to tolerate the challenging conditions typical of the continent. For these reasons, microbiologists have been drawn to Antarctica for decades. However, our understanding of which microbes thrive in Antarctic soils and how they to do so remains limited. To help resolve these knowledge gaps, we analyzed a collection of 200 archived Antarctic soils—from Livingston Island on the Antarctic Peninsula to Cape Hallett in northern Victoria Land. We analyzed the prokaryotic and fungal communities in these soils using both cultivation-independent marker gene sequencing and cultivation-dependent approaches (microbial isolation), paired with extensive soil geochemical analyses. Our cultivation-independent analyses indicate that colder, saltier, and drier soils harbor less diverse communities of bacteria and fungi, distinct from those found in soils with less challenging conditions. We also built a culture collection from a subset of these soils that encompasses more than 50 bacterial and fungal genera, including cold-tolerant organisms, such asCryobacteriumandCryomyces. By directly comparing the diversity of our cultured isolates against our cultivation-independent data, we show that many of the more abundant Antarctic taxa are not readily cultivated and highlight bacterial and fungal taxa that should be the focus of future cultivation efforts. Together, we hope that our collection of isolates, the comprehensive data compiled from the cultivation-independent analyses, and our geochemical analyses will serve as a community resource to accelerate the study of Antarctic soil microbes. 

Abstract Environmental DNA (eDNA) is frequently used to infer distributions of microorganisms in Antarctica. Their distributions relative to environmental variables are, in turn, sometimes used to infer their physiological range (and a relationship between the two is generally assumed for conservation purposes). We sought to determine whether ecological inferences based on distributions accurately reflect tolerances of the organisms concerned, using 249 legacy non-marine samples from a latitudinal gradient between 72 and 86°S, Antarctica. A cyanobacterium, a heterotrophic bacterium, two eukaryotic algae, two fungi, and a moss were isolated into culture, and their field distributions inferred using eDNA analysis of the samples above. Tolerances of each organism with respect to environmental predictors were then inferred from the eDNA distribution and metadata using Generalised Additive Models. We then measured growth of the cultured isolates in response to a set of these predictors. Laboratory responses were then compared to inferences from the eDNA/metadata. Predictions from eDNA/metadata agreed with the results of physiological laboratory experiments for strains that were detected at high taxonomic resolution in the field samples. However, errors were never completely eliminated, and direct contradictions occurred when strains were represented at lower taxonomic resolution in the field data. We found that accurate ecological inference from eDNA studies would be best achieved via maximising both taxonomic resolution (through marker choice/read length) and ecological signal (through careful sampling design and rigorous metadata collection). 

The genusPseudogymnoascusincludes several species frequently isolated from extreme environments worldwide, including cold environments such as Antarctica. This study describes three new species ofPseudogymnoascus—P. russussp. nov.,P. irelandiaesp. nov., andP. ramosussp. nov.—isolated from Antarctic soils. These species represent the firstPseudogymnoascustaxa to be formally described from Antarctic soil samples, expanding our understanding of fungal biodiversity in this extreme environment. Microscopic descriptions of asexual structures from living cultures, along with measurements of cultural characteristics and growth on various media types at different temperatures, identify three distinct new species. In addition, phylogenetic analyses based on five gene regions (ITS, LSU, MCM7, RPB2, TEF1) and whole-genome proteomes place these new species within three distinct previously described clades:P. irelandiaein clade K,P. ramosusin clade Q, andP. russusin clade B. These results provide further evidence of the extensive undescribed diversity ofPseudogymnoascusin high-latitude soils. This study contributes to the growing body of knowledge on Antarctic mycology and the broader ecology of psychrophilic and psychrotolerant fungi. 

This data package offers comprehensive insights into Antarctic soil microbial diversity and composition. From 2003 to 2023, a total of 186 samples were collected from diverse locations spanning the Antarctic Peninsula to East Antarctica, representing a wide range of environmental gradients and climatic conditions. Soils were stored at -20°C to preserve their integrity for downstream analyses. This data package integrates cultivation-independent sequencing of prokaryotic and fungal communities alongside a robust cultivation-dependent culture collection to enable direct comparisons across microbial diversity assessment methods. Accompanying geochemical, physicochemical, and environmental parameters provide critical context for biogeographical analyses, offering a valuable resource for studying microbial adaptations and community dynamics in extreme Antarctic environments. 

ABSTRACT Microbial communities can be structured by both deterministic and stochastic processes, but the relative importance of these processes remains unknown. The ambiguity partly arises from an inability to disentangle soil microbial processes from confounding factors, such as aboveground plant communities or anthropogenic disturbance. In this study, we characterized the relative contributions of determinism and stochasticity to assembly processes of soil bacterial communities across a large environmental gradient of undisturbed Antarctic soils. We hypothesized that harsh soils would impose a strong environmental selection on microbial communities, whereas communities in benign soils would be structured largely by dispersal. Contrary to our expectations, dispersal was the dominant assembly mechanism across the entire soil environmental gradient, including benign environments. The microbial community composition reflects slowly changing soil conditions and dispersal limitation of isolated sites. Thus, stochastic processes, as opposed to deterministic, are primary drivers of soil ecosystem assembly across space at our study site. This is especially surprising given the strong environmental constraints on soil microorganisms in one of the harshest environments on the planet, suggesting that dispersal could be a driving force in microbial community assembly in soils worldwide. IMPORTANCE Because of their diversity and ubiquity, microbes provide an excellent means to tease apart how natural communities are structured. In general, ecologists believe that stochastic assembly processes, like random drift and dispersal, should dominate in benign environments while deterministic processes, like environmental filtering, should be prevalent in harsh environments. To help resolve this debate, we analyzed microbial community composition in pristine Antarctic soils devoid of human influence or plant communities for eons. Our results demonstrate that dispersal limitation is a surprisingly potent force of community limitation throughout all soil conditions. Thus, dispersal appears to be a driving force of microbial community assembly, even in the harshest of conditions.