Interactions of Fungi and Algae from the Greenland Ice Sheet

Snow algae exhibit diverse motile behaviors and thermal responses

Snow algal blooms influence snow and glacier melt dynamics, yet the mechanisms involved in community assemblage, development, and dispersal are not well understood. While microbial swimming behavior contributes significantly to the productivity and organization of aquatic and terrestrial microbiomes, the potential impact of algal cell motility in melting snow on the formation of visible, large-scale surface bloom patterns is largely unknown. Here, using video tracking and phototaxis experiments of unique isolates, we evaluated the motility of diverse snow algal taxa from green, red, and golden colored snow blooms in response to light and thermal gradients. We show that many species are efficient cryophilic microswimmers with speed thermal optima below 10°C although taxa with cryotolerant swimming traits were also identified. The significant motility of snow algae at low temperatures, a result of specialized adaptations, supports the importance of active movement in the life histories of algae inhabiting snow meltwater. However, diversity in swimming performance and behavior reveal a range of evolutionary outcomes and sensitivity of motile life stages to dynamic environments.IMPORTANCESwimming motility is a fundamental mechanism that controls the assembly, structure, and productivity of microbiomes across diverse environments and is highly sensitive to temperature. Especially, the role of cell swimming activity in algal bloom formation at the very low temperatures of snowmelt has been hypothesized, but not studied. By examining the movement patterns of snow algae and modeling the thermal response curves of swimming speed, the data reveal the key role of active cell movement that may have further important impacts on the microbial ecology and melt rates of snow and ice in polar and alpine regions.

Single-cell imaging reveals efficient nutrient uptake and growth of microalgae darkening the Greenland Ice Sheet

Blooms of dark pigmented microalgae accelerate glacier and ice sheet melting by reducing the surface albedo. However, the role of nutrient availability in regulating algal growth on the ice remains poorly understood. Here, we investigate glacier ice algae on the Greenland Ice Sheet, providing single-cell measurements of carbon:nitrogen:phosphorus (C:N:P) ratios and assimilation rates of dissolved inorganic carbon (DIC), ammonium and nitrate following nutrient amendments. The single-cell analyses reveal high C:N and C:P atomic ratios in algal biomass as well as intracellular P storage. DIC assimilation rates are not enhanced by ammonium, nitrate, or phosphate addition. Our combined results demonstrate that glacier ice algae can optimise nutrient uptake, facilitating the potential colonization of newly exposed bare ice surfaces without the need for additional nutrient inputs. This adaptive strategy is particularly important given accelerated climate warming and the expansion of melt areas on the Greenland Ice Sheet.

Ecological interactions in glacier environments: a review of studies on a model Alpine glacier

Glaciers host a variety of cold-adapted taxa, many of which have not yet been described. Interactions among glacier organisms are even less clear. Understanding ecological interactions is crucial to unravelling the functioning of glacier ecosystems, particularly in light of current glacier retreat. Through a review of the existing literature, we aim to provide a first overview of the biodiversity, primary production, trophic networks, and matter flow of a glacier ecosystem. We use the Forni Glacier (Central Italian Alps) - one of the best studied alpine glaciers in the world - as a model system for our literature review and integrate additional original data. We reveal the importance of allochthonous organic matter inputs, of Cyanobacteria and eukaryotic green algae in primary production, and the key role of springtails (Vertagopus glacialis) on the glacier surface in sustaining populations of two apex terrestrial predators: Nebria castanea (Coleoptera: Carabidae) and Pardosa saturatior (Araneae: Lycosidae). The cryophilic tardigrade Cryobiotus klebelsbergi is the apex consumer in cryoconite holes. This short food web highlights the fragility of nodes represented by invertebrates, contrasting with structured microbial communities in all glacier habitats. Although further research is necessary to quantify the ecological interactions of glacier organisms, this review summarises and integrates existing knowledge about the ecological processes on alpine glaciers and supports the importance of glacier-adapted organisms in providing ecosystem services.

A review of recently introduced Aspergillus, Penicillium, Talaromyces and other Eurotiales species

The order Eurotiales is diverse and includes species that impact our daily lives in many ways. In the past, its taxonomy was difficult due to morphological similarities, which made accurate identification of species difficult. This situation improved and stabilised with recent taxonomic and nomenclatural revisions that modernised Aspergillus, Penicillium and Talaromyces. This was mainly due to the availability of curated accepted species lists and the publication of comprehensive DNA sequence reference datasets. This has also led to a sharp increase in the number of new species described each year with the accepted species lists in turn also needing regular updates. The focus of this study was to review the 160 species described between the last list of accepted species published in 2020 until 31 December 2022. To review these species, single-gene phylogenies were constructed and GCPSR (Genealogical Concordance Phylogenetic Species Recognition) was applied. Multi-gene phylogenetic analyses were performed to further determine the relationships of the newly introduced species. As a result, we accepted 133 species (37 Aspergillus, two Paecilomyces, 59 Penicillium, two Rasamsonia, 32 Talaromyces and one Xerochrysium), synonymised 22, classified four as doubtful and created a new combination for Paraxerochrysium coryli, which is classified in Xerochrysium. This brings the number of accepted species to 453 for Aspergillus, 12 for Paecilomyces, 535 for Penicillium, 14 for Rasamsonia, 203 for Talaromyces and four for Xerochrysium. We accept the newly introduced section Tenues (in Talaromyces), and series Hainanici (in Aspergillus sect. Cavernicolarum) and Vascosobrinhoana (in Penicillium sect. Citrina). In addition, we validate the invalidly described species Aspergillus annui and A. saccharicola, and series Annuorum (in Aspergillus sect. Flavi), introduce a new combination for Dichlaena lentisci (type of the genus) and place it in a new section in Aspergillus subgenus Circumdati, provide an updated description for Rasamsonia oblata, and list excluded and recently synonymised species that were previously accepted. This study represents an important update of the accepted species lists in Eurotiales. Taxonomic novelties: New sections: Aspergillus section Dichlaena Visagie, Kocsubé & Houbraken. New series: Aspergillus series Annuorum J.J. Silva, B.T. Iamanaka, Frisvad. New species: Aspergillus annui J.J. Silva, M.H.P. Fungaro, Frisvad, M.H. Taniwaki & B.T. Iamanaka; Aspergillus saccharicola J.J. Silva, Frisvad, M.H.P. Fungaro, M.H. Taniwaki & B.T. Iamanaka. New combinations: Aspergillus lentisci (Durieu & Mont.) Visagie, Malloch, L. Kriegsteiner, Samson & Houbraken; Xerochrysium coryli (Crous & Decock) Visagie & Houbraken. Citation: Visagie CM, Yilmaz N, Kocsubé S, Frisvad JC, Hubka V, Samson RA, Houbraken J (2024). A review of recently introduced Aspergillus, Penicillium, Talaromyces and other Eurotiales species. Studies in Mycology 107: 1-66. doi: 10.3114/sim.2024.107.01.

The exometabolome of microbial communities inhabiting bare ice surfaces on the southern Greenland Ice Sheet

Microbial blooms colonize the Greenland Ice Sheet bare ice surface during the ablation season and significantly reduce its albedo. On the ice surface, microbes are exposed to high levels of irradiance, freeze-thaw cycles, and low nutrient concentrations. It is well known that microorganisms secrete metabolites to maintain homeostasis, communicate with other microorganisms, and defend themselves. Yet, the exometabolome of supraglacial microbial blooms, dominated by the pigmented glacier ice algae Ancylonema alaskanum and Ancylonema nordenskiöldii, remains thus far unstudied. Here, we use a high-resolution mass spectrometry-based untargeted metabolomics workflow to identify metabolites in the exometabolome of microbial blooms on the surface of the southern tip of the Greenland Ice Sheet. Samples were collected every 6 h across two diurnal cycles at 5 replicate sampling sites with high similarity in community composition, in terms of orders and phyla present. Time of sampling explained 46% (permutational multivariate analysis of variance [PERMANOVA], pseudo-F = 3.7771, p = 0.001) and 27% (PERMANOVA, pseudo-F = 1.8705, p = 0.001) of variance in the exometabolome across the two diurnal cycles. Annotated metabolites included riboflavin, lumichrome, tryptophan, and azelaic acid, all of which have demonstrated roles in microbe-microbe interactions in other ecosystems and should be tested for potential roles in the development of microbial blooms on bare ice surfaces.

Additions to the Knowledge of the Fungal Order Eurotiales in Korea: Eight Undescribed Species

Eurotiales is a relatively large order of Ascomycetes, well-known for their ability to produce secondary metabolites with potential beneficial applications. To understand their diversity and distribution, different environmental sources including soil, freshwater, insect, and indoor air were investigated. Eight strains of Eurotiales were isolated and identified based on their morphological characters and a multi-gene phylogenetic analysis of the ITS, BenA, CaM, and RPB2 regions. We identified eight taxa that were previously not reported from Korea: Aspergillus baeticus, A. griseoaurantiacus, A. spinulosporus, Penicillium anthracinoglaciei, P. labradorum, P. nalgiovense, Talaromyces atroroseus, and T. georgiensis. Detailed descriptions, illustrations, and phylogenetic tree for the eight new records species are presented, and information regarding the records is also discussed.

The undiscovered biosynthetic potential of the Greenland Ice Sheet microbiome

The Greenland Ice Sheet is a biome which is mainly microbially driven. Several different niches can be found within the glacial biome for those microbes able to withstand the harsh conditions, e.g., low temperatures, low nutrient conditions, high UV radiation in summer, and contrasting long and dark winters. Eukaryotic algae can form blooms during the summer on the ice surface, interacting with communities of bacteria, fungi, and viruses. Cryoconite holes and snow are also habitats with their own microbial community. Nevertheless, the microbiome of supraglacial habitats remains poorly studied, leading to a lack of representative genomes from these environments. Under-investigated extremophiles, like those living on the Greenland Ice Sheet, may provide an untapped reservoir of chemical diversity that is yet to be discovered. In this study, an inventory of the biosynthetic potential of these organisms is made, through cataloging the presence of biosynthetic gene clusters in their genomes. There were 133 high-quality metagenome-assembled genomes (MAGs) and 28 whole genomes of bacteria obtained from samples of the ice sheet surface, cryoconite, biofilm, and snow using culturing-dependent and -independent approaches. AntiSMASH and BiG-SCAPE were used to mine these genomes and subsequently analyze the resulting predicted gene clusters. Extensive sets of predicted Biosynthetic Gene Clusters (BGCs) were collected from the genome collection, with limited overlap between isolates and MAGs. Additionally, little overlap was found in the biosynthetic potential among different environments, suggesting specialization of organisms in specific habitats. The median number of BGCs per genome was significantly higher for the isolates compared to the MAGs. The most talented producers were found among Proteobacteria. We found evidence for the capacity of these microbes to produce antimicrobials, carotenoid pigments, siderophores, and osmoprotectants, indicating potential survival mechanisms to cope with extreme conditions. The majority of identified BGCs, including those in the most prevalent gene cluster families, have unknown functions, presenting a substantial potential for bioprospecting. This study underscores the diverse biosynthetic potential in Greenland Ice Sheet genomes, revealing insights into survival strategies and highlighting the need for further exploration and characterization of these untapped resources.

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.

Seven New Species of Eurotiales (Ascomycota) Isolated from Tidal Flat Sediments in China

Tidal flats have been reported to contain many microorganisms and play a critical role in maintaining biodiversity. In surveys of filamentous fungi from tidal flat sediments in China, seven new species of Eurotiales were discovered and described. Morphological characteristics and DNA sequence analyses of combined datasets of the BenA, CaM, and RPB2 regions support their placements and recognition as new species. Aspergillus liaoningensis sp. nov. and A. plumeriae sp. nov. belong to sections Candidi and Flavipedes of subgenus Circumdati, and A. subinflatus sp. nov. is a member of section Cremei of subgenus Cremei. Penicillium danzhouense sp. nov., P. tenue sp. nov., and P. zhanjiangense sp. nov. are attributed to sections Exilicaulis and Lanata-Divaricata of subgenus Aspergilloides. Talaromyces virens sp. nov. is in section Talaromyces. Detailed descriptions and illustrations of these novel taxa are provided. Their differences from close relatives were compared and discussed.

Understanding Fungi in Glacial and Hypersaline Environments

Hypersaline waters and glacial ice are inhospitable environments that have low water activity and high concentrations of osmolytes. They are inhabited by diverse microbial communities, of which extremotolerant and extremophilic fungi are essential components. Some fungi are specialized in only one of these two environments and can thrive in conditions that are lethal to most other life-forms. Others are generalists, highly adaptable species that occur in both environments and tolerate a wide range of extremes. Both groups efficiently balance cellular osmotic pressure and ion concentration, stabilize cell membranes, remodel cell walls, and neutralize intracellular oxidative stress. Some species use unusual reproductive strategies. Further investigation of these adaptations with new methods and carefully designed experiments under ecologically relevant conditions will help predict the role of fungi in hypersaline and glacial environments affected by climate change, decipher their stress resistance mechanisms and exploit their biotechnological potential.

High prevalence of parasitic chytrids infection of glacier algae in cryoconite holes in Alaska

Glacier algae, which are photosynthetic microbes growing on ice, considerably reduce the surface albedo of glaciers and accelerate their melting rate. Although the growth of glacier algae can be suppressed by parasitic chytrids, the impact of chytrids on algal populations is still largely unknown. In this study, we described the morphology of the chytrid infecting the glacier alga Ancylonema nordenskioeldii and quantified the prevalence of infection in different habitats on a mountain glacier in Alaska, USA. Microscopic observations revealed three different morphological types of chytrids with distinct rhizoid shapes. Variations in the size of the sporangia were probably because of their different growth stages, indicating that they actively propagated on the glacier. The prevalence of infection did not vary among sites with different elevations but was substantially higher in cryoconite holes (20%) than on ice surfaces (4%) at all sites. This indicates that cryoconite holes are hot spots for chytrid infections of glacier algae, and the dynamics of cryoconite holes might affect the host-parasite interactions between chytrids and the glacier algae, which may in turn alter surface albedo and ice melting.

Diversity analysis of leaf endophytic fungi and rhizosphere soil fungi of Korean Epimedium at different growth stages

BACKGROUND

Rhizosphere fungi and endophytic fungi play key roles in plant growth and development; however, their role in the growth of Epimedium koreanum Nakai at different stages remains unclear. Here, we used the Illumina MiSeq system, a high-throughput sequencing technology, to study the endophytic fungi and rhizosphere microbiome of Korean Epimedium.

RESULTS

Epimedium koreanum Nakai rhizosphere soil and leaves had highly diverse fungal communities during the growth process. The relative abundance of soil fungi in the rhizosphere stage was higher than that of leaf endophytic fungi in the early growth stage, but the overall abundance was basically equal. Sebacina is a significantly divergent fungal genera, and Sebacina sp. are present among leaf fungi species in the rhizosphere soil of Epimedium koreanum Nakai. Sebacina sp. can move to each other in rhizosphere soil fungi and leaf endophytes. VIF (variance inflation factor) analysis showed that soluble salt, whole nitrogen, alkaline lysis nitrogen, whole phosphorus, total potassium, and fast-acting potassium are useful environmental factors for rhizosphere soil and leaf endophytic fungi: potassium, total nitrogen, whole phosphorus, and three environmental factors were significantly and positively associated with the relative abundance of Sebacina sp.

CONCLUSIONS

(1) This study is the first to clarify the species diversity of fungi in Epimedium koreanum Nakai leaf and rhizosphere soil. (2) Different fungal communities of rhizosphere soil fungi and leaf endophytic fungi at different growth stages of Epimedium koreanum Nakai were examined. (3) Sebacina sp. can move to each other between rhizosphere soil fungi and leaf endophytic fungi. (4) Nitrogen, phosphorus and potassium elements in the environment have a significant positive effect on the relative abundance of Sebacina sp.

Pigment signatures of algal communities and their implications for glacier surface darkening

Blooms of pigmented algae darken the surface of glaciers and ice sheets, thereby enhancing solar energy absorption and amplifying ice and snow melt. The impacts of algal pigment and community composition on surface darkening are still poorly understood. Here, we characterise glacier ice and snow algal pigment signatures on snow and bare ice surfaces and study their role in photophysiology and energy absorption on three glaciers in Southeast Greenland. Purpurogallin and astaxanthin esters dominated the glacier ice and snow algal pigment pools (mass ratios to chlorophyll a of 32 and 56, respectively). Algal biomass and pigments impacted chromophoric dissolved organic matter concentrations. Despite the effective absorption of astaxanthin esters at wavelengths where incoming irradiance peaks, the cellular energy absorption of snow algae was 95% lower than anticipated from their pigmentation, due to pigment packaging. The energy absorption of glacier ice algae was consequently ~ 5 × higher. On bare ice, snow algae may have locally contributed up to 13% to total biological radiative forcing, despite contributing 44% to total biomass. Our results give new insights into the impact of algal community composition on bare ice energy absorption and biomass accumulation during snow melt.