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Background: Tramway Ridge, a geothermal Antarctic Specially Protected Area (elevation 3340 m) located near the summit of Mount Erebus, is home to a unique community composed of cosmopolitan surface-associated micro-organisms and abundant, poorly understood subsurface-associated microorganisms. Here, we use shotgun metagenomics to compare the functional capabilities of this community to those found elsewhere on Earth and to infer in situ diversity and metabolic capabilities of abundant subsurface taxa., Results: We found that the functional potential in this community is most similar to that found in terrestrial hydrothermal environments (hot springs, sediments) and that the two dominant organisms in the subsurface carry high rates of in situ diversity which was taken as evidence of potential endemicity. They were found to be facultative anaerobic heterotrophs that likely share a pool of nitrogenous organic compounds while specializing in different carbon compounds., Conclusions: Metagenomic insights have provided a detailed understanding of the microbe-based ecosystem found in geothermally heated fumaroles at Tramway Ridge. This approach enabled us to compare Tramway Ridge with other microbial systems, identify potentially endemic taxa and elucidate the key metabolic pathways that may enable specific organisms to dominate the ecosystem., Competing Interests: Declarations. Ethics approval and consent to participate: Not applicable. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Mt. Erebus, Antarctica, is the southernmost active volcano in the world and harbors diverse geothermally unique ecosystems, including "Subglacial" and "Exposed" features, surrounded by a vast desert of ice and snow. Previous studies, while limited in scope, have highlighted the unique and potentially endemic biota of Mt. Erebus. Here, we provide an amplicon-based biodiversity study across all domains of life and all types of geothermal features, with physicochemical and biological data from 48 samples (39 Exposed and 9 Subglacial) collected through various field seasons. We found potentially high taxonomic novelty among prokaryotes and fungi, supporting past hypotheses of high endemism due to the distinctive and isolated environment; in particular, the large number of taxonomically divergent fungal sequences was surprising. We found that different site types had unique physicochemistry and biota; Exposed sites were warmer than Subglacial (median: 40°C versus 10°C for Exposed and Subglacial, respectively) and tended to have more photosynthetic organisms (Cyanobacteria and Chlorophyta). Subglacial sites had more Actinobacteriota, correlated with greater concentrations of Ca and Mg present. Our results also suggest potential human impacts on these remote, highly significant sites, finding evidence for fungal taxa normally associated with wood decay. In this study, we provide a blueprint for future work aimed at better understanding the novel biota of Mt. Erebus., (© The Author(s) 2024. Published by Oxford University Press on behalf of FEMS.)

Human land use changes are threatening the integrity and health of coastal ecosystems worldwide. Intensified land use for anthropogenic purposes increases sedimentation rates, pollutants, and nutrient concentrations into adjacent coastal areas, often with detrimental effects on marine life and ecosystem functioning. However, how these factors interact to influence ecosystem health in mangrove forests is poorly understood. This study investigates the effects of catchment human land use on mangrove forest architecture and sedimentary attributes at a landscape-scale. Thirty sites were selected along a gradient of human land use within a narrow latitudinal range, to minimise the effects of varying climatic conditions. Land use was quantified using spatial analysis tools with existing land use databases (LCDB5). Twenty-six forest architectural and sedimentary variables were collected from each site. The results revealed a significant effect of human land use on ten out of 26 environmental variables. Eutrophication, characterised by changes in redox potential, pH, and sediment nutrient concentrations, was strongly associated with increasing human land use. The δ 15 N values of sediments and leaves also indicated increased anthropogenic nitrogen input. Furthermore, the study identified a positive correlation between human land use and tree density, indicating that increased nutrient delivery from catchments contributes to enhanced mangrove growth. Propagule and seedling densities were also positively correlated with human land use, suggesting potential recruitment success mechanisms. This research underpins the complex interactions between human land use and mangrove ecosystems, revealing changes in carbon dynamics, potential alterations in ecosystem services, and a need for holistic management approaches that consider the interconnectedness of species and their environment. These findings provide essential insights for regional ecosystem models, coastal management, and restoration strategies to address the impacts of human pressures on temperate mangrove forests, even in estuaries that may be relatively healthy., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Background: Isolating the effects of deterministic variables (e.g., physicochemical conditions) on soil microbial communities from those of neutral processes (e.g., dispersal) remains a major challenge in microbial ecology. In this study, we disturbed soil microbial communities of two McMurdo Dry Valleys of Antarctica exhibiting distinct microbial biogeographic patterns, both devoid of aboveground biota and different in macro- and micro-physicochemical conditions. We modified the availability of water, nitrogen, carbon, copper ions, and sodium chloride salts in a laboratory-based experiment and monitored the microbial communities for up to two months. Our aim was to mimic a likely scenario in the near future, in which similar selective pressures will be applied to both valleys. We hypothesized that, given their unique microbial communities, the two valleys would select for different microbial populations when subjected to the same disturbances., Results: The two soil microbial communities, subjected to the same disturbances, did not respond similarly as reflected in both 16S rRNA genes and transcripts. Turnover of the two microbial communities showed a contrasting response to the same environmental disturbances and revealed different potentials for adaptation to change. These results suggest that the heterogeneity between these microbial communities, reflected in their strong biogeographic patterns, was maintained even when subjected to the same selective pressure and that the 'rare biosphere', at least in these samples, were deeply divergent and did not act as a reservoir for microbiota that enabled convergent responses to change in environmental conditions., Conclusions: Our findings strongly support the occurrence of endemic microbial communities that show a structural resilience to environmental disturbances, spanning a wide range of physicochemical conditions. In the highly arid and nutrient-limited environment of the Dry Valleys, these results provide direct evidence of microbial biogeographic patterns that can shape the communities' response in the face of future environmental changes., (© 2024. The Author(s).)

Water availability is the dominant driver of microbial community structure and function in desert soils. However, these habitats typically only receive very infrequent large-scale water inputs (e.g., from precipitation and/or run-off). In light of recent studies, the paradigm that desert soil microorganisms are largely dormant under xeric conditions is questionable. Gene expression profiling of microbial communities in desert soils suggests that many microbial taxa retain some metabolic functionality, even under severely xeric conditions. It, therefore, follows that other, less obvious sources of water may sustain the microbial cellular and community functionality in desert soil niches. Such sources include a range of precipitation and condensation processes, including rainfall, snow, dew, fog, and nocturnal distillation, all of which may vary quantitatively depending on the location and geomorphological characteristics of the desert ecosystem. Other more obscure sources of bioavailable water may include groundwater-derived water vapour, hydrated minerals, and metabolic hydro-genesis. Here, we explore the possible sources of bioavailable water in the context of microbial survival and function in xeric desert soils. With global climate change projected to have profound effects on both hot and cold deserts, we also explore the potential impacts of climate-induced changes in water availability on soil microbiomes in these extreme environments.

The dispersion of microorganisms through the atmosphere is a continual and essential process that underpins biogeography and ecosystem development and function. Despite the ubiquity of atmospheric microorganisms globally, specific knowledge of the determinants of atmospheric microbial diversity at any given location remains unresolved. Here we describe bacterial diversity in the atmospheric boundary layer and underlying soil at twelve globally distributed locations encompassing all major biomes, and characterise the contribution of local and distant soils to the observed atmospheric community. Across biomes the diversity of bacteria in the atmosphere was negatively correlated with mean annual precipitation but positively correlated to mean annual temperature. We identified distinct non-randomly assembled atmosphere and soil communities from each location, and some broad trends persisted across biomes including the enrichment of desiccation and UV tolerant taxa in the atmospheric community. Source tracking revealed that local soils were more influential than distant soil sources in determining observed diversity in the atmosphere, with more emissive semi-arid and arid biomes contributing most to signatures from distant soil. Our findings highlight complexities in the atmospheric microbiota that are relevant to understanding regional and global ecosystem connectivity., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.)

Microbiota inhabiting the Dry Valleys of Antarctica are subjected to multiple stressors that can damage deoxyribonucleic acid (DNA) such as desiccation, high ultraviolet light (UV) and multiple freeze-thaw cycles. To identify novel or highly-divergent DNA-processing enzymes that may enable effective DNA repair, we have sequenced metagenomes from 30 sample-sites which are part of the most extensive Antarctic biodiversity survey undertaken to date. We then used these to construct wide-ranging sequence similarity networks from protein-coding sequences and identified candidate genes involved in specialized repair processes including unique nucleases as well as a diverse range of adenosine triphosphate (ATP) -dependent DNA ligases implicated in stationary-phase DNA repair processes. In one of the first direct investigations of enzyme function from these unique samples, we have heterologously expressed and assayed a number of these enzymes, providing insight into the mechanisms that may enable resident microbes to survive these threats to their genomic integrity., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Rzoska-Smith, Stelzer, Monterio, Cary and Williamson.)

Microbial biogeography studies, in particular for geothermal-associated habitats, have focused on spatial patterns and/or individual sites, which have limited ability to describe the dynamics of ecosystem behaviour. Here, we report the first comprehensive temporal study of bacterial and archaeal communities from an extensive range of geothermal features in Aotearoa-New Zealand. One hundred and fifteen water column samples from 31 geothermal ecosystems were taken over a 34-month period to ascertain microbial community stability (control sites), community response to both natural and anthropogenic disturbances in the local environment (disturbed sites) and temporal variation in spring diversity across different pH values (pH 3, 5, 7, 9) all at a similar temperature of 60-70°C (pH sites). Identical methodologies were employed to measure microbial diversity via 16S rRNA gene amplicon sequencing, along with 44 physicochemical parameters from each feature, to ensure confidence in comparing samples across timeframes. Our results indicated temperature and associated groundwater physicochemistry were the most likely parameters to vary stochastically in these geothermal features, with community abundances rather than composition more readily affected by a changing environment. However, variation in pH (pH ±1) had a more significant effect on community structure than temperature (±20°C), with alpha diversity failing to adequately measure temporal microbial disparity in geothermal features outside of circumneutral conditions. While a substantial physicochemical disturbance was required to shift community structures at the phylum level, geothermal ecosystems were resilient at this broad taxonomic rank and returned to a pre-disturbed state if environmental conditions re-established. These findings highlight the diverse controls between different microbial communities within the same habitat-type, expanding our understanding of temporal dynamics in extreme ecosystems., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Power, Lowe, Carere, McDonald, Cary and Stott.)

Free-living terrestrial mites (Acari) have persisted through numerous glacial cycles in Antarctica. Very little is known, however, of their genetic diversity and distribution, particularly within the Ross Sea region. To redress this gap, we sampled mites throughout the Ross Sea region, East Antarctica, including Victoria Land and the Queen Maud Mountains (QMM), covering a latitudinal range of 72-85 °S, as well as Lauft Island near Mt. Siple (73 °S) in West Antarctica and Macquarie Island (54 o S) in the sub-Antarctic. We assessed genetic diversity using mitochondrial cytochrome c oxidase subunit I gene sequences (COI-5P DNA barcode region), and also morphologically identified voucher specimens. We obtained 130 sequences representing four genera: Nanorchestes ( n = 30 sequences), Stereotydeus ( n = 46), Coccorhagidia ( n = 18) and Eupodes ( n = 36). Tree-based analyses (maximum likelihood) revealed 13 genetic clusters, representing as many as 23 putative species indicated by barcode index numbers (BINs) from the Barcode of Life Datasystems (BOLD) database. We found evidence for geographically-isolated cryptic species, e.g., within Stereotydeus belli and S. punctatus , as well as unique genetic groups occurring in sympatry (e.g., Nanorchestes spp. in QMM). Collectively, these data confirm high genetic divergence as a consequence of geographic isolation over evolutionary timescales. From a conservation perspective, additional targeted sampling of understudied areas in the Ross Sea region should be prioritised, as further diversity is likely to be found in these short-range endemic mites.

Venenivibrio stagnispumantis strain CP.B2 T is a thermophilic, chemolithoautotrophic bacterium from the family Hydrogenothermaceae (phylum Aquificota ), isolated from Champagne Pool in the Waiotapu geothermal field, Aotearoa-New Zealand. The genome consists of 1.73 Mbp in 451 contigs with a 30.8 mol% G+C content.

Climate warming in Antarctica involves major shifts in plant distribution and productivity. This study aims to unravel the plasticity and acclimation potential of Bryum argenteum var. muticum , a cosmopolitan moss species found in Antarctica. By comparing short-term, closed-top chamber warming experiments which mimic heatwaves, with in situ seasonal physiological rates from Cape Hallett, Northern Victoria Land, we provide insights into the general inherent resilience of this important Antarctic moss and into its adaptability to longer-term threats and stressors associated with climate change. Our findings show that B. argenteum can thermally acclimate to mitigate the effects of increased temperature under both seasonal changes and short-term pulse warming events. Following pulse warming, this species dramatically increased its carbon uptake, measured as net photosynthesis, while reductions in carbon losses, measured as dark respiration, were not observed. Rapid growth of new shoots may have confounded the effects on respiration. These results demonstrate the high physiological plasticity of this species, with acclimation occurring within only 7 days. We show that this Antarctic moss species appears to have a high level of resilience and that fast acclimation processes allow it to potentially benefit from both short-term and long-term climatic changes.

Antarctic deserts, such as the McMurdo Dry Valleys (MDV), represent extremely cold and dry environments. Consequently, MDV are suitable for studying the environment limits on the cycling of key elements that are necessary for life, like nitrogen. The spatial distribution and biogeochemical drivers of nitrogen-cycling pathways remain elusive in the Antarctic deserts because most studies focus on specific nitrogen-cycling genes and/or organisms. In this study, we analyzed metagenome and relevant environmental data of 32 MDV soils to generate a complete picture of the nitrogen-cycling potential in MDV microbial communities and advance our knowledge of the complexity and distribution of nitrogen biogeochemistry in these harsh environments. We found evidence of nitrogen-cycling genes potentially capable of fully oxidizing and reducing molecular nitrogen, despite the inhospitable conditions of MDV. Strong positive correlations were identified between genes involved in nitrogen cycling. Clear relationships between nitrogen-cycling pathways and environmental parameters also indicate abiotic and biotic variables, like pH, water availability, and biological complexity that collectively impose limits on the distribution of nitrogen-cycling genes. Accordingly, the spatial distribution of nitrogen-cycling genes was more concentrated near the lakes and glaciers. Association rules revealed non-linear correlations between complex combinations of environmental variables and nitrogen-cycling genes. Association rules for the presence of denitrification genes presented a distinct combination of environmental variables from the remaining nitrogen-cycling genes. This study contributes to an integrative picture of the nitrogen-cycling potential in MDV., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Pascoal, Areosa, Torgo, Branco, Baptista, Lee, Cary and Magalhães.)

Assessing the resilience of polar biota to climate change is essential for predicting the effects of changing environmental conditions for ecosystems. Collembola are abundant in terrestrial polar ecosystems and are integral to food-webs and soil nutrient cycling. Using available literature, we consider resistance (genetic diversity; behavioural avoidance and physiological tolerances; biotic interactions) and recovery potential for polar Collembola. Polar Collembola have high levels of genetic diversity, considerable capacity for behavioural avoidance, wide thermal tolerance ranges, physiological plasticity, generalist-opportunistic feeding habits and broad ecological niches. The biggest threats to the ongoing resistance of polar Collembola are increasing levels of dispersal (gene flow), increased mean and extreme temperatures, drought, changing biotic interactions, and the arrival and spread of invasive species. If resistance capacities are insufficient, numerous studies have highlighted that while some species can recover from disturbances quickly, complete community-level recovery is exceedingly slow. Species dwelling deeper in the soil profile may be less able to resist climate change and may not recover in ecologically realistic timescales given the current rate of climate change. Ultimately, diverse communities are more likely to have species or populations that are able to resist or recover from disturbances. While much of the Arctic has comparatively high levels of diversity and phenotypic plasticity; areas of Antarctica have extremely low levels of diversity and are potentially much more vulnerable to climate change., Competing Interests: The authors declare no financial conflicts associated with this research. Brent J. Sinclair is Editor-in-Chief of Current Research in Insect Science. Given his role, he had no involvement in the evaluation or peer review of this manuscript, and has no access to information regarding its peer review., (© 2022 The Authors. Published by Elsevier B.V.)

Mt. Erebus, Antarctica, is the world's southernmost active volcano and is unique in its isolation from other major active volcanic systems and its distinctive geothermal systems. Using 16S rRNA gene amplicon sequencing and physicochemical analyses, we compared samples collected at two contrasting high-temperature (50°C-65°C) sites on Mt. Erebus: Tramway Ridge, a weather-protected high biomass site, and Western Crater, an extremely exposed low biomass site. Samples were collected along three thermal gradients, one from Western Crater and two within Tramway Ridge, which allowed an examination of the heterogeneity present at Tramway Ridge. We found distinct soil compositions between the two sites, and to a lesser extent within Tramway Ridge, correlated with disparate microbial communities. Notably, pH, not temperature, showed the strongest correlation with these differences. The abundance profiles of several microbial groups were different between the two sites; class Nitrososphaeria amplicon sequence variants (ASVs) dominated the community profiles at Tramway Ridge, whereas Acidobacteriotal ASVs were only found at Western Crater. A co-occurrence network, paired with physicochemical analyses, allowed for finer scale analysis of parameters correlated with differential abundance profiles, with various parameters (total carbon, total nitrogen, soil moisture, soil conductivity, sulfur, phosphorous, and iron) showing significant correlations. ASVs assigned to Chloroflexi classes Ktedonobacteria and Chloroflexia were detected at both sites. Based on the known metabolic capabilities of previously studied members of these groups, we predict that chemolithotrophy is a common strategy in this system. These analyses highlight the importance of conducting broader-scale metagenomics and cultivation efforts at Mt. Erebus to better understand this unique environment., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Noell, Baptista, Smith, McDonald, Lee, Stott, Amend and Cary.)

The space-for-time substitution approach provides a valuable empirical assessment to infer temporal effects of disturbance from spatial gradients. Applied to predict the response of different ecosystems under current climate change scenarios, it remains poorly tested in microbial ecology studies, partly due to the trophic complexity of the ecosystems typically studied. The McMurdo Dry Valleys (MDV) of Antarctica represent a trophically simple polar desert projected to experience drastic changes in water availability under current climate change scenarios. We used this ideal model system to develop and validate a microbial space-for-time sampling approach, using the variation of geochemical profiles that follow alterations in water availability and reflect past changes in the system. Our framework measured soil electrical conductivity, pH, and water activity in situ to geochemically define 17 space-for-time transects from the shores of four dynamic and two static Dry Valley lakes. We identified microbial taxa that are consistently responsive to changes in wetness in the soils and reliably associated with long-term dry or wet edaphic conditions. Comparisons between transects defined at static (open-basin) and dynamic (closed-basin) lakes highlighted the capacity for geochemically defined space-for-time gradients to identify lasting deterministic impacts of historical changes in water presence on the structure and diversity of extant microbial communities. We highlight the potential for geochemically defined space-for-time transects to resolve legacy impacts of environmental change when used in conjunction with static and dynamic scenarios, and to inform future environmental scenarios through changes in the microbial community structure, composition, and diversity., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Monteiro, Marshall, Hawes, Lee, McDonald and Cary.)

Lecideoid lichens as dominant vegetation-forming organisms in the climatically harsh areas of the southern part of continental Antarctica show clear preferences in relation to environmental conditions (i.e. macroclimate). 306 lichen samples were included in the study, collected along the Ross Sea coast (78°S-85.5°S) at six climatically different sites. The species compositions as well as the associations of their two dominant symbiotic partners (myco- and photobiont) were set in context with environmental conditions along the latitudinal gradient. Diversity values were nonlinear with respect to latitude, with the highest alpha diversity in the milder areas of the McMurdo Dry Valleys (78°S) and the most southern areas (Durham Point, 85.5°S; Garden Spur, 84.5°S), and lowest in the especially arid and cold Darwin Area (~ 79.8°S). Furthermore, the specificity of mycobiont species towards their photobionts decreased under more severe climate conditions. The generalist lichen species Lecanora fuscobrunnea and Lecidea cancriformis were present in almost all habitats, but were dominant in climatically extreme areas. Carbonea vorticosa, Lecidella greenii and Rhizoplaca macleanii were confined to milder areas. In summary, the macroclimate is considered to be the main driver of species distribution, making certain species useful as bioindicators of climate conditions and, consequently, for assessing the consequences of climate change., (© 2021. The Author(s).)

Ecosystem feedbacks in response to ocean acidification can amplify or diminish diel pH oscillations in productive coastal waters. Benthic microalgae generate such oscillations in sediment porewater and here we ask how CO 2 enrichment (acidification) of the overlying seawater alters these in the absence and presence of biogenic calcite. We placed a 1-mm layer of ground oyster shells, mimicking the arrival of dead calcifying biota (+Calcite), or sand (Control) onto intact silt sediment cores, and then gradually increased the pCO 2 in the seawater above half of +Calcite and Control cores from 472 to 1216 μatm (pH 8.0 to 7.6, CO 2 :HCO 3 - from 4.8 to 9.6 × 10 -4 ). Porewater [O 2 ] and [H + ] microprofiles measured 16 d later showed that this enrichment had decreased the O 2 penetration depth (O 2 -pd) in +Calcite and Control, indicating a metabolic response. In CO 2 -enriched seawater: (1) sediment biogeochemical processes respectively added and removed more H + to and from the sediment porewater in darkness and light, than in ambient seawater increasing the amplitude of the diel porewater [H + ] oscillations, and (2) in darkness, calcite dissolution in +Calcite sediment decreased the porewater [H + ] below that in overlying seawater, reversing the sediment-seawater H + flux and decreasing the amplitude of diel [H + ] oscillations. This dissolution did not, however, counter the negative effect of CO 2 enrichment on O 2 -pd. We now hypothesise that feedback to CO 2 enrichment-an increase in the microbial reoxidation of reduced solutes with O 2 -decreased the sediment O 2 -pd and contributed to the enhanced porewater acidification., (© 2021. The Author(s).)

Climate change is driving dramatic variability in sea ice dynamics, a key driver in polar marine ecosystems. Projected changes in Antarctica suggest that regional warming will force dramatic shifts in sea ice thickness and persistence, altering sea ice-associated primary production and deposition to the seafloor. To improve our understanding of the impacts of sea ice change on benthic ecosystems, we directly compared the benthic microbial communities underlying first-year sea ice (FYI) and multi-year sea ice (MYI). Using two tractable coastal habitats in McMurdo Sound, Antarctica, where FYI (Cape Evans) and MYI (New Harbour) prevail, we show that the structure and composition of the benthic microbial communities reflect the legacy of sea ice dynamics. At Cape Evans, an enrichment of known heterotrophic algal polysaccharide degrading taxa (e.g., Flavobacteriaceae , unclassified Gammaproteobacteria , and Rubritaleaceae ) and sulfate-reducing bacteria (e.g., Desulfocapsaceae ) correlated with comparatively higher chlorophyll a (14.2±0.8μgg -1 ) and total organic carbon content (0.33%±0.04), reflecting increased productivity and seafloor deposition beneath FYI. Conversely, at New Harbour, an enrichment of known archaeal (e.g., Nitrosopumilaceae ) and bacterial (e.g., Woeseiaceae and Nitrospiraceae ) chemoautotrophs was common in sediments with considerably lower chlorophyll a (1.0±0.24μgg -1 ) and total organic carbon content (0.17%±0.01), reflecting restricted productivity beneath MYI. We also report evidence of a submarine discharge of sub-permafrost brine from Taylor Valley into New Harbour. By comparing our two study sites, we show that under current climate-warming scenarios, changes to sea ice productivity and seafloor deposition are likely to initiate major shifts in benthic microbial communities, with heterotrophic organic matter degradation processes becoming increasingly important. This study provides the first assessment of how legacy sea ice conditions influence benthic microbial communities in Antarctica, contributing insight into sea ice-benthic coupling and ecosystem functioning in a polar environment., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Currie, Marshall, Lohrer, Cummings, Seabrook and Cary.)

Cyanobacterial mats in the Antarctic Dry Valleys are photosynthetic microbial ecosystems living at the extreme of conditions on Earth with respect to temperature, light, water and nutrient availability. They are metabolically active for about 8 weeks during the austral summer when temperatures briefly rise above freezing and glacial and lake melt waters are available. There is much to learn about the biogeochemical impact of mats in these environments and the microbial communities associated with them. Our data demonstrate that these mats attain surprisingly high rates of carbon (CO 2 ) and dinitrogen (N 2 ) fixation when liquid water is available, in some cases comparable to rates in warmer temperate or tropical environments. C and N 2 fixation in Dry Valley mats in turn substantially elevate dissolved organic C and inorganic N pools and thereby promote enhanced microbial secondary production. Moreover, the microbial community fingerprint of these mats is unique compared with the more ubiquitous dry soils that do not contain mats. Components of the heterotrophic microbiota may also contribute substantially to N inputs through N 2 fixation., (Copyright © 2020 Sohm, Niederberger, Parker, Tirindelli, Gunderson, Cary, Capone and Carpenter.)

The Dry Valleys of Antarctica are a unique ecosystem of simple trophic structure, where the abiotic factors that influence soil bacterial communities can be resolved in the absence of extensive biotic interactions. This study evaluated the degree to which aspects of topographic, physicochemical and spatial variation explain patterns of bacterial richness and community composition in 471 soil samples collected across a 220 square kilometer landscape in Southern Victoria Land. Richness was most strongly influenced by physicochemical soil properties, particularly soil conductivity, though significant trends with several topographic and spatial variables were also observed. Structural equation modeling (SEM) supported a final model in which variation in community composition was best explained by physicochemical variables, particularly soil water content, and where the effects of topographic variation were largely mediated through their influence on physicochemical variables. Community dissimilarity increased with distance between samples, and though most of this variation was explained by topographic and physicochemical variation, a small but significant relationship remained after controlling for this environmental variation. As the largest survey of terrestrial bacterial communities of Antarctica completed to date, this work provides fundamental knowledge of the Dry Valleys ecosystem, and has implications globally for understanding environmental factors that influence bacterial distributions., (© FEMS 2020.)

Polar ecosystems are generally limited in nitrogen (N) nutrients, and the patchy availability of N is partly determined by biological pathways, such as nitrification, which are carried out by distinctive prokaryotic functional groups. The activity and diversity of microorganisms are generally strongly influenced by environmental conditions. However, we know little of the attributes that control the distribution and activity of specific microbial functional groups, such as nitrifiers, in extreme cold environments and how they may respond to change. To ascertain relationships between soil geochemistry and the ecology of nitrifying microbial communities, we carried out a laboratory-based manipulative experiment to test the selective effect of key geochemical variables on the activity and abundance of ammonia-oxidizing communities in soils from the McMurdo Dry Valleys of Antarctica. We hypothesized that nitrifying communities, adapted to different environmental conditions within the Dry Valleys, will have distinct responses when submitted to similar geochemical disturbances. In order to test this hypothesis, soils from two geographically distant and geochemically divergent locations, Miers and Beacon Valleys, were incubated over 2 months under increased conductivity, ammonia concentration, copper concentration, and organic matter content. Amplicon sequencing of the 16S rRNA gene and transcripts allowed comparison of the response of ammonia-oxidizing Archaea (AOA) and ammonia-oxidizing Bacteria (AOB) to each treatment over time. This approach was combined with measurements of 15 NH 4 + oxidation rates using 15 N isotopic additions. Our results showed a higher potential for nitrification in Miers Valley, where environmental conditions are milder relative to Beacon Valley. AOA exhibited better adaptability to geochemical changes compared to AOB, particularly to the increase in copper and conductivity. AOA were also the only nitrifying group found in Beacon Valley soils. This laboratorial manipulative experiment provided new knowledge on how nitrifying groups respond to changes on key geochemical variables of Antarctic desert soils, and we believe these results offer new insights on the dynamics of N cycling in these ecosystems.

The McMurdo Dry Valleys (MDV) in Antarctica harbor a diverse assemblage of mat-forming diazotrophic cyanobacteria that play a key role in nitrogen cycling. Prior research showed that heterotrophic diazotrophs also make a substantial contribution to nitrogen fixation in MDV. The goals of this study were to survey autotrophic and heterotrophic diazotrophs across the MDV to investigate factors that regulate the distribution and relative ecological roles of each group. Results indicated that diazotrophs were present only in samples with mats, suggesting a metabolic coupling between autotrophic and heterotrophic diazotrophs. Analysis of 16S rRNA and nifH gene sequences also showed that diazotrophs were significantly correlated to the broader bacterial community, while co-occurrence network analysis revealed potential interspecific interactions. Consistent with previous studies, heterotrophic diazotrophs in MDV were diverse, but largely limited to lakes and their outlet streams, or other environments protected from desiccation. Despite the limited distribution, heterotrophic diazotrophs may make a substantial contribution to the nitrogen budget of MDV due to larger surface area and longer residence times of lakes. This work contributes to our understanding of key drivers of bacterial community structure in polar deserts and informs future efforts to investigate the contribution of nitrogen fixation to MDV ecosystems., (© FEMS 2020.)

The McMurdo Dry Valleys constitute the largest ice-free region of Antarctica and one of the most extreme deserts on Earth. Despite the low temperatures, dry and poor soils and katabatic winds, some microbes are able to take advantage of endolithic microenvironments, inhabiting the pore spaces of soil and constituting photosynthesis-based communities. We isolated a green microalga, Endolithella mcmurdoensis gen. et sp. nov, from an endolithic sandstone sample collected in the McMurdo Dry Valleys (Victoria Land, East Antarctica) during the K020 expedition, in January 2013. The single non-axenic isolate (E. mcmurdoensis LEGE Z-009) exhibits cup-shaped chloroplasts, electron-dense bodies, and polyphosphate granules but our analysis did not reveal any diagnostic morphological characters. On the basis of phylogenetic analysis of the 18S rRNA (SSU) gene, the isolate was found to represent a new genus within the family Chlorellaceae., (© 2019 Phycological Society of America.)

Microbial eukaryotes have important roles in marine food webs, but their diversity and activities in hydrothermal vent ecosystems are poorly characterized. In this study, we analyzed microbial eukaryotic communities associated with bacterial (Beggiatoa) mats in the 2,000 m deep-sea Guaymas Basin hydrothermal vent system using 18S rRNA gene high-throughput sequencing of the V4 region. We detected 6,954 distinct Operational Taxonomic Units (OTUs) across various mat systems. Of the sequences that aligned with known protistan phylotypes, most were affiliated with alveolates (especially dinoflagellates and ciliates) and cercozoans. OTU richness and community structure differed among sediment habitats (e.g. different mat types and cold sediments away from mats). Additionally, full-length 18S rRNA genes amplified and cloned from single cells revealed the identities of some of the most commonly encountered, active ciliates in this hydrothermal vent ecosystem. Observations and experiments were also conducted to demonstrate that ciliates were trophically active and ingesting fluorescent bacteria or Beggiatoa trichomes. Our work suggests that the active and diverse protistan community at the Guaymas Basin hydrothermal vent ecosystem likely consumes substantial amounts of bacterial biomass, and that the different habitats, often defined by distances of just a few 10s of cm, select for particular assemblages and levels of diversity., (© 2019 International Society of Protistologists.)

Dispersal is a critical yet poorly understood factor underlying macroecological patterns in microbial communities 1 . Airborne microbial transport is assumed to occupy a central role in determining dispersal outcomes 2,3 , and extra-range dispersal has important implications for predicting ecosystem resilience and response to environmental change 4 . One of the most pertinent biomes in this regard is Antarctica, given its geographic isolation and vulnerability to climate change and human disturbance 5 . Here, we report microbial diversity in near-ground and high-altitude air above the largest ice-free Antarctic habitat, as well as that of underlying soil microbial communities. We found that persistent local airborne inputs were unable to fully explain Antarctic soil community assembly. Comparison with airborne microbial diversity from high-altitude and non-polar sources suggests that strong selection occurs during long-range atmospheric transport. The influence of selection during airborne transit and at sink locations varied between microbial phyla. Overall, the communities from this isolated Antarctic ecosystem displayed limited connectivity to the non-polar microbial pool, and alternative sources of recruitment are necessary to fully explain extant soil diversity. Our findings provide critical insights into the role of airborne transport limitation in determining microbial biogeographic patterns.

Bacterial diversity from McMurdo Dry Valleys in Antarctica, the coldest desert on earth, has become more easily assessed with the development of High Throughput Sequencing (HTS) techniques. However, some of the diversity remains inaccessible by the power of sequencing. In this study, we combine cultivation and HTS techniques to survey actinobacteria and cyanobacteria diversity along different soil and endolithic micro-environments of Victoria Valley in McMurdo Dry Valleys. Our results demonstrate that the Dry Valleys actinobacteria and cyanobacteria distribution is driven by environmental forces, in particular the effect of water availability and endolithic environments clearly conditioned the distribution of those communities. Data derived from HTS show that the percentage of cyanobacteria decreases from about 20% in the sample closest to the water source to negligible values on the last three samples of the transect with less water availability. Inversely, actinobacteria relative abundance increases from about 20% in wet soils to over 50% in the driest samples. Over 30% of the total HTS data set was composed of actinobacterial strains, mainly distributed by 5 families: Sporichthyaceae , Euzebyaceae , Patulibacteraceae , Nocardioidaceae , and Rubrobacteraceae . However, the 11 actinobacterial strains isolated in this study, belonged to Micrococcaceae and Dermacoccaceae families that were underrepresented in the HTS data set. A total of 10 cyanobacterial strains from the order Synechococcales were also isolated, distributed by 4 different genera ( Nodosilinea , Leptolyngbya , Pectolyngbya , and Acaryochloris -like). In agreement with the cultivation results, Leptolyngbya was identified as dominant genus in the HTS data set. Acaryochloris -like cyanobacteria were found exclusively in the endolithic sample and represented 44% of the total 16S rRNA sequences, although despite our efforts we were not able to properly isolate any strain from this Acaryochloris -related group. The importance of combining cultivation and sequencing techniques is highlighted, as we have shown that culture-dependent methods employed in this study were able to retrieve actinobacteria and cyanobacteria taxa that were not detected in HTS data set, suggesting that the combination of both strategies can be usefull to recover both abundant and rare members of the communities.

The cold deserts of the McMurdo Dry Valleys (MDV), Antarctica, host a high level of microbial diversity. Microbial composition and biomass in arid vs. ephemerally wetted regions are distinctly different, with wetted communities representing hot spots of microbial activity that are important zones for biogeochemical cycling. While climatic change is likely to cause wetting in areas not historically subject to wetting events, the responses of microorganisms inhabiting arid soils to water addition is unknown. The purpose of this study was to observe how an associated, yet non-wetted microbial community responds to an extended addition of water. Water from a stream was diverted to an adjacent area of arid soil with changes in microbial composition and activities monitored via molecular and biochemical methods over 7 weeks. The frequency of genetic signatures related to both prokaryotic and eukaryotic organisms adapted to MDV aquatic conditions increased during the limited 7 week period, indicating that the soil community was transitioning into a typical "high-productivity" MDV community. This work is consistent with current predictions that MDV microbial communities in arid regions are highly sensitive to climate change, and further supports the notion that changes in community structure and associated biogeochemical cycling may occur much more rapidly than predicted.

Abiotic and biotic factors control ecosystem biodiversity, but their relative contributions remain unclear. The ultraoligotrophic ecosystem of the Antarctic Dry Valleys, a simple yet highly heterogeneous ecosystem, is a natural laboratory well-suited for resolving the abiotic and biotic controls of community structure. We undertook a multidisciplinary investigation to capture ecologically relevant biotic and abiotic attributes of more than 500 sites in the Dry Valleys, encompassing observed landscape heterogeneities across more than 200 km 2 . Using richness of autotrophic and heterotrophic taxa as a proxy for functional complexity, we linked measured variables in a parsimonious yet comprehensive structural equation model that explained significant variations in biological complexity and identified landscape-scale and fine-scale abiotic factors as the primary drivers of diversity. However, the inclusion of linkages among functional groups was essential for constructing the best-fitting model. Our findings support the notion that biotic interactions make crucial contributions even in an extremely simple ecosystem., Competing Interests: The authors declare no competing interests.

Abiotic factors are major determinants of soil animal distributions and their dominant role is pronounced in extreme ecosystems, with biotic interactions seemingly playing a minor role. We modelled co-occurrence and distribution of the three nematode species that dominate the soil food web of the McMurdo Dry Valleys (Antarctica). Abiotic factors, other biotic groups, and autocorrelation all contributed to structuring nematode species distributions. However, after removing their effects, we found that the presence of the most abundant nematode species greatly, and negatively, affected the probability of detecting one of the other two species. We observed similar patterns in relative abundances for two out of three pairs of species. Harsh abiotic conditions alone are insufficient to explain contemporary nematode distributions whereas the role of negative biotic interactions has been largely underestimated in soil. The future challenge is to understand how the effects of global change on biotic interactions will alter species coexistence., Competing Interests: The authors declare no competing interests.

Groundwater is a major source of New Zealand's water supply and supports base flows in rivers. Microbial communities in groundwater ecosystems mediate biogeochemical processes, and it is therefore crucial to understand microbial diversity in these ecosystems. We analysed bacterial assemblages from 35 New Zealand groundwater monitoring sites with varying hydrogeochemical conditions across the country. Proteobacteria was the most abundant phylum, and Variovorax represented the most common taxon. Pseudomonas, Burkholderia, Acidovorax, Janthinobacterium, Polaromonas and Caulobacter were the other common taxa. There was no Operational Taxonomic Unit (OTU) that was found in every one of the 35 samples. Here, we introduce a framework that has potential utility for groundwater ecosystem management, where the samples with similar microbial communities are grouped together into 'bioclusters'. Metabolic inferences derived from the taxonomic data were used to predict the oxygen requirements, metabolic potential and bacterial energy sources of each biocluster. Groundwater chemistry explains 59% of the variation in the relative abundance of all OTUs, with NO3-N, pH, DO, NH4-N, Fe, Br and SO4 displaying the strongest relationships to bioclusters. We propose that the biocluster framework, coupled with metabolic inferences derived from the taxonomic data, may have application outside New Zealand for on-going monitoring of the health of groundwater ecosystems.

Antarctic soil supports surface microbial communities that are dependent on ephemeral moisture. Understanding the response to availability of this resource is essential to predicting how the system will respond to climate change. The McMurdo Dry Valleys are the largest ice-free soil region in Antarctica. They are a hyper-arid polar desert with extremely limited moisture availability. Microbial colonization dominates this ecosystem but surprisingly little is known about how communities respond to changing moisture regimes. We utilized the natural model system provided by transiently wetted soil at lake margins in the Dry Valleys to interrogate microbial responses along a well-defined contiguous moisture gradient and disentangle responses between and within phyla. We identified a striking non-linear response among bacteria where at low moisture levels small changes resulted in a large impact on diversity. At higher moister levels community responses were less pronounced, resulting in diversity asymptotes. We postulate that whilst the main drivers of observed community diversity were deterministic, a switch in the major influence occurred from abiotic factors at low moisture levels to biotic interactions at higher moisture. Response between and within phyla was markedly different, highlighting the importance of taxonomic resolution in community analysis. Furthermore, we resolved apparent stochasticity at high taxonomic ranks as the result of deterministic interactions taking place at finer taxonomic and spatial scales. Overall the findings provide new insight on the response to moisture and this will be useful in advancing understanding of potential ecosystem responses in the threatened McMurdo Dry Valleys system.