The distinctive weathering crust habitat of a High Arctic glacier comprises discrete microbial micro-habitats.

Sunlight penetrates the ice surfaces of glaciers and ice sheets, forming a water-bearing porous ice matrix known as the weathering crust. This crust is home to a significant microbial community. Despite the potential implications of microbial processes in the weathering crust for glacial melting, biogeochemical cycles, and downstream ecosystems, there have been few explorations of its microbial communities. In our study, we used 16S rRNA gene sequencing and shotgun metagenomics of a Svalbard glacier surface catchment to characterise the microbial communities within the weathering crust, their origins and destinies, and the functional potential of the weathering crust metagenome. Our findings reveal that the bacterial community in the weathering crust is distinct from those in upstream and downstream habitats. However, it comprises two separate micro-habitats, each with different taxa and functional categories. The interstitial porewater is dominated by Polaromonas, influenced by the transfer of snowmelt, and exported via meltwater channels. In contrast, the ice matrix is dominated by Hymenobacter, and its metagenome exhibits a diverse range of functional adaptations. Given that the global weathering crust area and the subsequent release of microbes from it are strongly responsive to climate projections for the rest of the century, our results underscore the pressing need to integrate the microbiome of the weathering crust with other communities and processes in glacial ecosystems.

Dynamics and drivers of mycorrhizal fungi after glacier retreat.

The development of terrestrial ecosystems depends greatly on plant mutualists such as mycorrhizal fungi. The global retreat of glaciers exposes nutrient-poor substrates in extreme environments and provides a unique opportunity to study early successions of mycorrhizal fungi by assessing their dynamics and drivers. We combined environmental DNA metabarcoding and measurements of local conditions to assess the succession of mycorrhizal communities during soil development in 46 glacier forelands around the globe, testing whether dynamics and drivers differ between mycorrhizal types. Mycorrhizal fungi colonized deglaciated areas very quickly (< 10 yr), with arbuscular mycorrhizal fungi tending to become more diverse through time compared to ectomycorrhizal fungi. Both alpha- and beta-diversity of arbuscular mycorrhizal fungi were significantly related to time since glacier retreat and plant communities, while microclimate and primary productivity were more important for ectomycorrhizal fungi. The richness and composition of mycorrhizal communities were also significantly explained by soil chemistry, highlighting the importance of microhabitat for community dynamics. The acceleration of ice melt and the modifications of microclimate forecasted by climate change scenarios are expected to impact the diversity of mycorrhizal partners. These changes could alter the interactions underlying biotic colonization and belowground-aboveground linkages, with multifaceted impacts on soil development and associated ecological processes.

Bacterial diversity in a continuum from supraglacial habitats to a proglacial lake on the Tibetan Plateau.

Mountain glaciers are frequently assessed for their hydrological connectivity from glaciers to proglacial lakes. Ecological process on glacier surfaces and downstream ecosystems have often been investigated separately, but few studies have focused on the connectivity between the different glacial habitats. Therefore, it remains a limited understanding of bacterial community assembly across different habitats along the glacier hydrological continuum. In this study, we sampled along a glacial catchment from supraglacial snow, cryoconite holes, supraglacial runoff, ice-marginal moraine and proglacial lake on the Tibetan Plateau. The bacterial communities in these habitats were analyzed using high-throughput DNA sequencing of the 16S rRNA gene to determine the bacterial composition and assembly. Our results showed that each habitat hosted unique bacterial communities, with higher bacterial α-diversity in transitional habitats (e.g. runoff and ice-marginal moraine). Null model analysis indicated that deterministic processes predominantly shaped bacterial assembly in snow, cryoconite holes and lake, while stochastic process dominantly governed bacterial community in transitional habitats. Collectively, our findings suggest that local environment play a critical role in filtering bacterial community composition within glacier habitats. This study enhances our understanding of microbial assembly process in glacier environments and provides valuable insights into the factors governing bacterial community compositions across different habitats along the glacial hydrological continuum.

Adding experimental precision to the realism of field observations: Plant communities structure bacterial communities in a glacier forefield.

Ecological studies are aligned along a realism-precision continuum ranging from field observations to controlled lab experiments that each have their own strengths and limitations. Ecological insight may be most robust when combining approaches. In field observations along a successional gradient, we found correlations between plant species composition and soil bacterial communities, while bacterial Shannon diversity was unrelated to vegetation characteristics. To add a causal understanding of the processes of bacterial community assembly, we designed lab experiments to specifically test the influence of plant composition on bacterial communities. Using soil and seeds from our field site, we added different combinations of surface-sterilised seeds to homogenised soil samples in microcosms and analysed bacterial communities 4 months later. Our results confirmed the field observations suggesting that experimental plant community composition shaped bacterial community composition, while Shannon diversity was unaffected. These results reflect intimate plant-bacteria interactions that are important drivers of plant health and community assembly. While this study provided insights into the role of plants underlying the assembly of bacterial communities, we did not experimentally manipulate other drivers of community assembly such as abiotic factors. Therefore, we recommend multi-factorial laboratory experiments to quantify the relative importance of different factors contributing to microbial composition.

Rhizosphere assembly alters along a chronosequence in the Hallstätter glacier forefield (Dachstein, Austria).

Rhizosphere microbiome assembly is essential for plant health, but the temporal dimension of this process remains unexplored. We used a chronosequence of 150 years of the retreating Hallstätter glacier (Dachstein, Austria) to disentangle this exemplarily for the rhizosphere of three pioneer alpine plants. Time of deglaciation was an important factor shaping the rhizosphere microbiome. Microbiome functions, i.e. nutrient uptake and stress protection, were carried out by ubiquitous and cosmopolitan bacteria. The rhizosphere succession along the chronosequence was characterized by decreasing microbial richness but increasing specificity of the plant-associated bacterial community. Environmental selection is a critical factor in shaping the ecosystem, particularly in terms of plant-driven recruitment from the available edaphic pool. A higher rhizosphere microbial richness during early succession compared to late succession can be explained by the occurrence of cold-acclimated bacteria recruited from the surrounding soils. These taxa might be sensitive to changing habitat conditions that occurred at the later stages. A stronger influence of the plant host on the rhizosphere microbiome assembly was observed with increased time since deglaciation. Overall, this study indicated that well-adapted, ubiquitous microbes potentially support pioneer plants to colonize new ecosystems, while plant-specific microbes may be associated with the long-term establishment of their hosts.

Metagenomic insights into novel microbial lineages with distinct ecological functions in the Arctic glacier foreland ecosystems.

Land-terminating glaciers are retreating globally, resulting in the expansion of the ice-free glacier forelands (GFs). These GFs act as a natural laboratory to study microbial community succession, soil formation, and ecosystem development. Here, we have employed gene-centric and genome-resolved metagenomic approaches to disseminate microbial diversity, community structure, and their associated biogeochemical processes involved in the carbon, nitrogen, and sulfur cycling across three GF ecosystems. Here, we present a compendium of draft Metagenome Assembled Genomes (MAGs) belonging to bacterial (n = 899) and archaeal (n = 4) domains. These MAGs were reconstructed using a total of 27 shotgun metagenomic datasets obtained from three different GFs, including Midtre Lovénbreen glacier (Svalbard), Russell glacier (Greenland), and Storglaciaren (Sweden). The taxonomic classification revealed that 98% of MAGs remained unclassified at species levels, suggesting the presence of novel microbial lineages. The abundance of metabolic genes associated with carbon, nitrogen, and sulfur cycling pathways varied between and within the samples collected across the three GF ecosystems. Our findings indicate that MAGs from different GFs share close phylogenetic relationships but exhibit significant differences in abundance, distribution patterns, and metabolic functions. This compendium of novel MAGs, encompassing autotrophic, phototrophic, and chemolithoautotrophic microbial groups reconstructed from GF ecosystems, represents a valuable resource for further studies.

The distribution and drivers of microbial pigments in the cryoconite of four Tibetan glaciers.

Microbial pigments play a significant role in glacier albedo reduction, thereby contributing to accelerated glacier retreat. The Tibetan Plateau has experienced rapid glacier retreat in recent decades due to global warming, yet there is limited understanding of microbial pigment distribution in the region. Here, we investigated the pigment concentration and composition in cryoconite from four glaciers. Our results showed that chlorophylls were the dominant pigments in Palong No. 4 (PL) and Jiemayangzong (JMYZ) glaciers located in the south of the Tibetan Plateau, while carotenoids were dominant in Qiangyong (QY) and Tanggula (TGL) glaciers located in the central region. Additionally, the chlorophyll b to chlorophyll a ratio, which is an indicator of the algae-to-cyanobacteria ratio, was higher in PL and JMYZ compared to QY and TGL. By using Random Forest Regression and Structural Equation Modelling, we determined that the concentrations of chlorophyll a, chlorophyll b, and carotenoids were associated with autotrophic bacteria relative abundance, climatic factors, and a combination of bacterial and climatic factors, respectively. This study is the first to describe the distribution of microbial pigments in cryoconite from Tibetan glaciers, providing additional support on the influence of algal pigment on glacier retreat.

Salinity-controlled distribution of prokaryotic communities in the Arctic sea-ice melt ponds.

The thawing of snow and sea ice produces distinctive melt ponds on the surface of the Arctic sea ice, which covers a significant portion of the surface sea ice during summer. Melt-pond salinity impacts heat transfer to the ice below and the melting rate. It is widely known that melt ponds play a significant role in heat fluxes, ice-albedo feedback, and sea-ice energy balance. However, not much attention has been given to the fact that melt ponds also serve as a unique microbial ecosystem where microbial production begins as soon as they are formed. Here, we investigated the role of melt pond salinity in controlling the diversity and distribution of prokaryotic communities using culture-dependent and -independent approaches. The 16 S rRNA gene amplicon based next generation sequencing analysis retrieved a total of 14 bacterial phyla, consisting of 146 genera, in addition to two archaeal phyla. Further, the culture-dependent approaches of the study allowed for the isolation and identification of twenty-four bacterial genera in pure culture. Flavobacterium, Candidatus_Aquiluna, SAR11 clade, Polaribacter, Glaciecola, and Nonlabens were the dominant genera observed in the amplicon analysis. Whereas Actimicrobium, Rhodoglobus, Flavobacterium, and Pseudomonas were dominated in the culturable fraction. Our results also demonstrated that salinity, chlorophyll a, and dissolved organic carbon were the significant environmental variables controlling the prokaryotic community distribution in melt ponds. A significant community shift was observed in melt ponds when the salinity changed with the progression of melting and deepening of ponds. Different communities were found to be dominant in melt ponds with different salinity ranges. It was also observed that melt pond prokaryotic communities significantly differed from the surface ocean microbial community. Our observations suggest that complex prokaryotic communities develop in melt ponds immediately after its formation using dissolved organic carbon generated through primary production in the oligotrophic water.

Metagenome-assembled genomes from High Arctic glaciers highlight the vulnerability of glacier-associated microbiota and their activities to habitat loss.

The rapid warming of the Arctic is threatening the demise of its glaciers and their associated ecosystems. Therefore, there is an urgent need to explore and understand the diversity of genomes resident within glacial ecosystems endangered by human-induced climate change. In this study we use genome-resolved metagenomics to explore the taxonomic and functional diversity of different habitats within glacier-occupied catchments. Comparing different habitats within such catchments offers a natural experiment for understanding the effects of changing habitat extent or even loss upon Arctic microbiota. Through binning and annotation of metagenome-assembled genomes (MAGs) we describe the spatial differences in taxon distribution and their implications for glacier-associated biogeochemical cycling. Multiple taxa associated with carbon cycling included organisms with the potential for carbon monoxide oxidation. Meanwhile, nitrogen fixation was mediated by a single taxon, although diverse taxa contribute to other nitrogen conversions. Genes for sulphur oxidation were prevalent within MAGs implying the potential capacity for sulphur cycling. Finally, we focused on cyanobacterial MAGs, and those within cryoconite, a biodiverse microbe-mineral granular aggregate responsible for darkening glacier surfaces. Although the metagenome-assembled genome of Phormidesmis priestleyi, the cyanobacterium responsible for forming Arctic cryoconite was represented with high coverage, evidence for the biosynthesis of multiple vitamins and co-factors was absent from its MAG. Our results indicate the potential for cross-feeding to sustain P. priestleyi within granular cryoconite. Taken together, genome-resolved metagenomics reveals the vulnerability of glacier-associated microbiota to the deletion of glacial habitats through the rapid warming of the Arctic.

High prevalence of antibiotic-resistant and metal-tolerant cultivable bacteria in remote glacier environment.

Studies of antibiotic-resistant bacteria (ARB) have mainly originated from anthropic-influenced environments, with limited information from pristine environments. Remote cold environments are major reservoirs of ARB and have been determined in polar regions; however, their abundance in non-polar cold habitats is underexplored. This study evaluated antibiotics and metals resistance profiles, prevalence of antibiotic resistance genes (ARGs) and metals tolerance genes (MTGs) in 38 ARB isolated from the glacier debris and meltwater from Baishui Glacier No 1, China. Molecular identification displayed Proteobacteria (39.3%) predominant in debris, while meltwater was dominated by Actinobacteria (30%) and Proteobacteria (30%). Bacterial isolates exhibited multiple antibiotic resistance index values > 0.2. Gram-negative bacteria displayed higher resistance to antibiotics and metals than Gram-positive. PCR amplification exhibited distinct ARGs in bacteria dominated by ß-lactam genes blaCTX-M (21.1-71.1%), blaACC (21.1-60.5%), tetracycline-resistant gene tetA (21.1-60.5%), and sulfonamide-resistant gene sulI (18.4-52.6%). Moreover, different MTGs were reported in bacterial isolates, including mercury-resistant merA (21.1-63.2%), copper-resistant copB (18.4-57.9%), chromium-resistant chrA (15.8-44.7%) and arsenic-resistant arsB (10.5-44.7%). This highlights the co-selection and co-occurrence of MTGs and ARGs in remote glacier environments. Different bacteria shared same ARGs, signifying horizontal gene transfer between species. Strong positive correlation among ARGs and MTGs was reported. Metals tolerance range exhibited that Gram-negative and Gram-positive bacteria clustered distinctly. Gram-negative bacteria were significantly tolerant to metals. Amino acid sequences of blaACC,blaCTX-M,blaSHV,blaampC,qnrA, sulI, tetA and blaTEM revealed variations. This study presents promising ARB, harboring ARGs with variations in amino acid sequences, highlighting the need to assess the transcriptome study of glacier bacteria conferring ARGs and MTGs.

Exploring microbial diversity in Greenland Ice Sheet supraglacial habitats through culturing-dependent and -independent approaches.

The microbiome of Greenland Ice Sheet supraglacial habitats is still underinvestigated, and as a result there is a lack of representative genomes from these environments. In this study, we investigated the supraglacial microbiome through a combination of culturing-dependent and -independent approaches. We explored ice, cryoconite, biofilm, and snow biodiversity to answer: (1) how microbial diversity differs between supraglacial habitats, (2) if obtained bacterial genomes reflect dominant community members, and (3) how culturing versus high throughput sequencing changes our observations of microbial diversity in supraglacial habitats. Genomes acquired through metagenomic sequencing (133 high-quality MAGs) and whole genome sequencing (73 bacterial isolates) were compared to the metagenome assemblies to investigate abundance within the total environmental DNA. Isolates obtained in this study were not dominant taxa in the habitat they were sampled from, in contrast to the obtained MAGs. We demonstrate here the advantages of using metagenome SSU rRNA genes to reflect whole-community diversity. Additionally, we demonstrate a proof-of-concept of the application of in situ culturing in a supraglacial setting.

Methylotrophic Communities Associated with a Greenland Ice Sheet Methane Release Hotspot.

Subglacial environments provide conditions suitable for the microbial production of methane, an important greenhouse gas, which can be released from beneath the ice as a result of glacial melting. High gaseous methane emissions have recently been discovered at Russell Glacier, an outlet of the southwestern margin of the Greenland Ice Sheet, acting not only as a potential climate amplifier but also as a substrate for methane consuming microorganisms. Here, we describe the composition of the microbial assemblage exported in meltwater from the methane release hotspot at Russell Glacier and its changes over the melt season and as it travels downstream. We found that a substantial part (relative abundance 27.2% across the whole dataset) of the exported assemblage was made up of methylotrophs and that the relative abundance of methylotrophs increased as the melt season progressed, likely due to the seasonal development of the glacial drainage system. The methylotrophs were dominated by representatives of type I methanotrophs from the Gammaproteobacteria; however, their relative abundance decreased with increasing distance from the ice margin at the expense of type II methanotrophs and/or methylotrophs from the Alphaproteobacteria and Betaproteobacteria. Our results show that subglacial methane release hotspot sites can be colonized by microorganisms that can potentially reduce methane emissions.

Mineral substrate quality determines the initial soil microbial development in front of the Nordenskiöldbreen, Svalbard.

Substrate geochemistry is an important factor influencing early microbial development after glacial retreat on nutrient-poor geological substrates in the High Arctic. It is often difficult to separate substrate influence from climate because study locations are distant. Our study in the retreating Nordenskiöldbreen (Svalbard) is one of the few to investigate biogeochemical and microbial succession in two adjacent forefields, which share the same climatic conditions but differ in their underlying geology. The northern silicate forefield evolved in a classical chronosequence, where most geochemical and microbial parameters increased gradually with time. In contrast, the southern carbonate forefield exhibited high levels of nutrients and microbial biomass at the youngest sites, followed by a significant decline and then a gradual increase, which caused a rearrangement in the species and functional composition of the bacterial and fungal communities. This shuffling in the early stages of succession suggests that high nutrient availability in the bedrock could have accelerated early soil succession after deglaciation and thereby promoted more rapid stabilization of the soil and production of higher quality organic matter. Most chemical parameters and bacterial taxa converged with time, while fungi showed no clear pattern.

Microbial metabolomic responses to changes in temperature and salinity along the western Antarctic Peninsula.

Seasonal cycles within the marginal ice zones in polar regions include large shifts in temperature and salinity that strongly influence microbial abundance and physiology. However, the combined effects of concurrent temperature and salinity change on microbial community structure and biochemical composition during transitions between seawater and sea ice are not well understood. Coastal marine communities along the western Antarctic Peninsula were sampled and surface seawater was incubated at combinations of temperature and salinity mimicking the formation (cold, salty) and melting (warm, fresh) of sea ice to evaluate how these factors may shape community composition and particulate metabolite pools during seasonal transitions. Bacterial and algal community structures were tightly coupled to each other and distinct across sea-ice, seawater, and sea-ice-meltwater field samples, with unique metabolite profiles in each habitat. During short-term (approximately 10-day) incubations of seawater microbial communities under different temperature and salinity conditions, community compositions changed minimally while metabolite pools shifted greatly, strongly accumulating compatible solutes like proline and glycine betaine under cold and salty conditions. Lower salinities reduced total metabolite concentrations in particulate matter, which may indicate a release of metabolites into the labile dissolved organic matter pool. Low salinity also increased acylcarnitine concentrations in particulate matter, suggesting a potential for fatty acid degradation and reduced nutritional value at the base of the food web during freshening. Our findings have consequences for food web dynamics, microbial interactions, and carbon cycling as polar regions undergo rapid climate change.

Icescape-scale metabolomics reveals cyanobacterial and topographic control of the core metabolism of the cryoconite ecosystem of an Arctic ice cap.

Glaciers host ecosystems comprised of biodiverse and active microbiota. Among glacial ecosystems, less is known about the ecology of ice caps since most studies focus on valley glaciers or ice sheet margins. Previously we detailed the microbiota of one such high Arctic ice cap, focusing on cryoconite as a microbe-mineral aggregate formed by cyanobacteria. Here, we employ metabolomics at the scale of an entire ice cap to reveal the major metabolic pathways prevailing in the cryoconite of Foxfonna, central Svalbard. We reveal how geophysical and biotic processes influence the metabolomes of its resident cryoconite microbiota. We observed differences in amino acid, fatty acid, and nucleotide synthesis across the cap reflecting the influence of ice topography and the cyanobacteria within cryoconite. Ice topography influences central carbohydrate metabolism and nitrogen assimilation, whereas bacterial community structure governs lipid, nucleotide, and carotenoid biosynthesis processes. The prominence of polyamine metabolism and nitrogen assimilation highlights the importance of recycling nitrogenous nutrients. To our knowledge, this study represents the first application of metabolomics across an entire ice mass, demonstrating its utility as a tool for revealing the fundamental metabolic processes essential for sustaining life in supraglacial ecosystems experiencing profound change due to Arctic climate change-driven mass loss.

Empirical testing of cryoconite granulation: Role of cyanobacteria in the formation of key biogenic structure darkening glaciers in polar regions.

Cryoconite, the dark sediment on the surface of glaciers, often aggregates into oval or irregular granules serving as biogeochemical factories. They reduce a glacier's albedo, act as biodiversity hotspots by supporting aerobic and anaerobic microbial communities, constitute one of the organic matter (OM) sources on glaciers, and are a feeder for micrometazoans. Although cryoconite granules have multiple roles on glaciers, their formation is poorly understood. Cyanobacteria are ubiquitous and abundant engineers of cryoconite hole ecosystems. This study tested whether cyanobacteria may be responsible for cryoconite granulation as a sole biotic element. Incubation of Greenlandic, Svalbard, and Scandinavian cyanobacteria in different nutrient availabilities and substrata for growth (distilled water alone and water with quartz powder, furnaced cryoconite without OM, or powdered rocks from glacial catchment) revealed that cyanobacteria bind mineral particles into granules. The structures formed in the experiment resembled those commonly observed in natural cryoconite holes: they contained numerous cyanobacterial filaments protruding from aggregated mineral particles. Moreover, all examined strains were confirmed to produce extracellular polymeric substances (EPS), which suggests that cryoconite granulation is most likely due to EPS secretion by gliding cyanobacteria. In the presence of water as the only substrate for growth, cyanobacteria formed mostly carpet-like mats. Our data empirically prove that EPS-producing oscillatorialean cyanobacteria isolated from the diverse community of cryoconite microorganisms can form granules from mineral substrate and that the presence of the mineral substrate increases the probability of the formation of these important and complex biogeochemical microstructures on glaciers.

Synergistic effects of succession and microtopography of moraine on the fungal spatial diversity in a glacier forefield.

Primary succession and microtopography result in environmental changes and are important processes influencing the community assembly of soil fungi in the Arctic region. In glacier forefields that contain a series of moraine ridges, both processes contribute synchronously to fungal spatial diversity. To reveal the synergistic effects of succession and microtopography, we investigated the fungal community structure and environmental variables in the moraines of the Arklio Glacier, Ellesmere Island. The study sites were established at four locations from the top to the bottom of the ridge slope within each of the three moraine ridges of different post-glacial ages. The location-dependent community composition was equally diverse in both the initial and later stages of succession, suggesting that successional time could alter the effects of microtopography on the fungal community. Moreover, our results suggest that fungal communities at different locations follow different successional trajectories, even if they have passed through the same time lapse. Such a synergistic effect of succession and microtopography of moraines does not allow for parallel changes in fungal communities among moraines or among locations, suggesting that the moraine series contributes substantially to fungal spatial diversity in the glacier forefield.

Uncovering the processes of microbial community assembly in the near-surface sediments of a climate-sensitive glacier-fed lake.

Glacier-fed lakes are characterized by cold temperatures, high altitudes, and nutrient-poor conditions. Despite these challenging conditions, near-surface sediments of glacier-fed lakes harbor rich microbial communities that are critical for ecosystem functioning and serve as a bridge between aquatic ecology and the deep subsurface biosphere. However, there is limited knowledge regarding the microbial communities and their assembly processes in these sediments, which are highly vulnerable to climate change. To fill this knowledge gap, this study systematically analyzed environmental variables, microbial communities, diversity, co-occurrence relationships, and community assembly processes in the near-surface sediments of a glacier-fed lake in the Tibetan Plateau. The results revealed distinct vertical gradients in microbial diversity and subcommunities, highlighting the significant influence of selection processes and adaptive abilities on microbial communities. Specifically, specialists played a crucial role within the overall microbial communities. Microbial assembly was primarily driven by homogeneous selection, but its influence declined with increasing depth. In contrast, homogenizing dispersal showed an opposite pattern, and the bottom layer exhibited heterogeneous selection and undominated processes. These patterns of microbial assembly were primarily driven by environmental gradients, with significant contributions from processes associated to ammonium and organic matter deposition, as well as chemical precipitation in response to a warming climate. This study enhances our understanding of the microbial communities and assembly processes in the near-surface sediments of glacier-fed lakes and sheds light on geo-microbiological processes in climate-sensitive lacustrine sediments.

Atlantic water influx and sea-ice cover drive taxonomic and functional shifts in Arctic marine bacterial communities.

The Arctic Ocean is experiencing unprecedented changes because of climate warming, necessitating detailed analyses on the ecology and dynamics of biological communities to understand current and future ecosystem shifts. Here, we generated a four-year, high-resolution amplicon dataset along with one annual cycle of PacBio HiFi read metagenomes from the East Greenland Current (EGC), and combined this with datasets spanning different spatiotemporal scales (Tara Arctic and MOSAiC) to assess the impact of Atlantic water influx and sea-ice cover on bacterial communities in the Arctic Ocean. Densely ice-covered polar waters harboured a temporally stable, resident microbiome. Atlantic water influx and reduced sea-ice cover resulted in the dominance of seasonally fluctuating populations, resembling a process of "replacement" through advection, mixing and environmental sorting. We identified bacterial signature populations of distinct environmental regimes, including polar night and high-ice cover, and assessed their ecological roles. Dynamics of signature populations were consistent across the wider Arctic; e.g. those associated with dense ice cover and winter in the EGC were abundant in the central Arctic Ocean in winter. Population- and community-level analyses revealed metabolic distinctions between bacteria affiliated with Arctic and Atlantic conditions; the former with increased potential to use bacterial- and terrestrial-derived substrates or inorganic compounds. Our evidence on bacterial dynamics over spatiotemporal scales provides novel insights into Arctic ecology and indicates a progressing Biological Atlantification of the warming Arctic Ocean, with consequences for food webs and biogeochemical cycles.

Diversity and succession of chemolithoautotrophic microbial community along a recently deglaciation chronosequence on the Tibetan Plateau.

Glaciers in high-altitude mountain regions are retreating rapidly due to global warming, exposing deglaciated soils to extreme environmental conditions, and microbial colonization. However, knowledge about chemolithoautotrophic microbes, which play important roles in the development of oligotrophic deglaciated soils prior to plant colonization, remains elusive in deglaciated soils. Using real-time quantitative PCR and clone library methods, the diversity and succession of the chemolithoautotrophic microbial community harboring the cbbM gene across a 14-year deglaciation chronosequence on the Tibetan Plateau were determined. The abundance of the cbbM gene remained stable for the first 8 years after deglaciation and then increased significantly, ranging from 105 to 107 gene copies g-1 soil (P < 0.001). Soil total carbon increased gradually to 5-year deglaciation and then decreased. While total nitrogen and total sulfur levels were low throughout the chronosequence. Chemolithoautotrophs were related to Gammaproteobacteria and Betaproteobacteria, with the former dominating early deglaciated soils and the latter dominating older deglaciated soils. The diversity of chemolithoautotrophs was high in mid-age deglaciated soils (6-year-old) and was low in early (3-year-old) and older deglaciated soils (12-year-old). Our findings revealed that chemolithoautotrophic microbes colonize deglaciated soils quickly and follow a clear successional pattern across recently deglaciated chronosequences.