Opportunistic fungi found in fairy rings are present on different moss species in the Antarctic Peninsula

Pathogenic potential of an environmental Aspergillus fumigatus strain recovered from soil of Pygoscelis papua (Gentoo penguins) colony in Antarctica

Aspergillus fumigatus is a common opportunistic pathogen in different animals, including birds such as penguins. For the first time, a fungal strain identified as A. fumigatus was isolated from soil in the nests of gentoo penguins, Pygoscelis papua, on Livingston Island, South Shetland Islands (maritime Antarctica). This isolate (A. fumigatus UFMGCB 11829) displayed a series of potentially pathogenic characteristics in vitro. We evaluated its detailed molecular taxonomy and submitted the A. fumigatus UFMGCB 11829 Antarctic strain to in vivo pathogenic modelling. The isolate was confirmed to represent A. fumigatus morphological and phylogenetic analysis showed that it was closely related to A. fumigatus sequences reported from animals, immunosuppressed humans, storage grains, plants and soils. The strain displayed the best mycelial growth and conidia production at 37 ºC; however, it was also able to grow and produce conidia at 15º, demonstrating its capability to survive and colonize penguin nest at least in the summer season in maritime Antarctica. In pathogenicity tests, healthy mice did not showed symptoms of infection; however, 50% lethality was observed in immunosuppressed mice that were inoculated with 106 and 107 spores. Lethality increased to 100% when inoculated with 108 spores. Our data highlight the potential pathogenicity of opportunistic A. fumigatus that may be present in the Antarctic, and the risks of both their further transfer within Antarctica and outwards to other continents, risks which may be exacerbated due global climatic changes.

Microbial successional pattern along a glacier retreat gradient from Byers Peninsula, Maritime Antarctica

The retreat of glaciers in Antarctica has increased in the last decades due to global climate change, influencing vegetation expansion, and soil physico-chemical and biological attributes. However, little is known about soil microbiology diversity in these periglacial landscapes. This study characterized and compared bacterial and fungal diversity using metabarcoding of soil samples from the Byers Peninsula, Maritime Antarctica. We identified bacterial and fungal communities by amplification of bacterial 16 S rRNA region V3-V4 and fungal internal transcribed spacer 1 (ITS1). We also applied 14C dating on soil organic matter (SOM) from six profiles. Physico-chemical analyses and attributes associated with SOM were evaluated. A total of 14,048 bacterial ASVs were obtained, and almost all samples had 50% of their sequences assigned to Actinobacteriota and Proteobacteria. Regarding the fungal community, Mortierellomycota, Ascomycota and Basidiomycota were the main phyla from 1619 ASVs. We found that soil age was more relevant than the distance from the glacier, with the oldest soil profile (late Holocene soil profile) hosting the highest bacterial and fungal diversity. The microbial indices of the fungal community were correlated with nutrient availability, soil reactivity and SOM composition, whereas the bacterial community was not correlated with any soil attribute. The bacterial diversity, richness, and evenness varied according to presence of permafrost and moisture regime. The fungal community richness in the surface horizon was not related to altitude, permafrost, or moisture regime. The soil moisture regime was crucial for the structure, high diversity and richness of the microbial community, specially to the bacterial community. Further studies should examine the relationship between microbial communities and environmental factors to better predict changes in this terrestrial ecosystem.

Cryptic fungal diversity revealed by DNA metabarcoding in historic wooden structures at Whalers Bay, Deception Island, maritime Antarctic

We provide the first assessment of fungal diversity associated with historic wooden structures at Whalers Bay (Heritage Monument 71), Deception Island, maritime Antarctic, using DNA metabarcoding. We detected a total of 177 fungal amplicon sequence variants (ASVs) dominated by the phyla Ascomycota, Basidiomycota, Mortierellomycota, Chytridiomycota, Monoblepharomycota, Rozellomycota, and Zoopagomycota. The assemblages were dominated by Helotiales sp. 1 and Herpotrichiellaceae sp. 1. Functional assignments indicated that the taxa detected were dominated by saprotrophic, plant and animal pathogenic, and symbiotic taxa. Metabarcoding revealed the presence of a rich and complex fungal community, which may be due to the wooden structures acting as baits attracting taxa to niches sheltered against extreme conditions, generating a hotspot for fungi in Antarctica. The sequences assigned included both cosmopolitan and endemic taxa, as well as potentially unreported diversity. The detection of DNA assigned to taxa of human and animal opportunistic pathogens raises a potential concern as Whalers Bay is one of the most popular visitor sites in Antarctica. The use of metabarcoding to detect DNA present in environmental samples does not confirm the presence of viable or metabolically active fungi and further studies using different culturing conditions and media, different growth temperatures and incubation periods, in combination with further molecular approaches such as shotgun sequencing are now required to clarify the functional ecology of these fungi.

A scoping review of bryophyte microbiota: diverse microbial communities in small plant packages

Plant health depends not only on the condition of the plant itself but also on its diverse community of microbes, or microbiota. Just like the better-studied angiosperms, bryophytes (mosses, liverworts, and hornworts) harbor diverse communities of bacteria, archaea, fungi, and other microbial eukaryotes. Bryophytes are increasingly recognized as important model systems for understanding plant evolution, development, physiology, and symbiotic interactions. Much of the work on bryophyte microbiota in the past focused on specific symbiont types for each bryophyte group, but more recent studies are taking a broader view acknowledging the coexistence of diverse microbial communities in bryophytes. Therefore, this review integrates studies of bryophyte microbes from both perspectives to provide a holistic view of the existing research for each bryophyte group and on key themes. The systematic search also reveals the taxonomic and geographic biases in this field, including a severe under-representation of the tropics, very few studies on viruses or eukaryotic microbes beyond fungi, and a focus on mycorrhizal fungi studies in liverworts. Such gaps may have led to errors in conclusions about evolutionary patterns in symbiosis. This analysis points to a wealth of future research directions that promise to reveal how the distinct life cycles and physiology of bryophytes interact with their microbiota.

Diversity of Fungi Present in Permafrost in the South Shetland Islands, Maritime Antarctic

We assess the fungal diversity present in permafrost from different islands in the South Shetland Islands archipelago, maritime Antarctic, using next-generation sequencing (NGS). We detected 1,003,637 fungal DNA reads representing, in rank abundance order, the phyla Ascomycota, Mortierellomycota, Basidiomycota, Chytridiomycota, Rozellomycota, Mucoromycota, Calcarisporiellomycota and Zoopagomycota. Ten taxa were dominant these being, in order of abundance, Pseudogymnoascus appendiculatus, Penicillium sp., Pseudogymnoascus roseus, Penicillium herquei, Curvularia lunata, Leotiomycetes sp., Mortierella sp. 1, Mortierella fimbricystis, Fungal sp. 1 and Fungal sp. 2. A further 38 taxa had intermediate abundance and 345 were classified as rare. The total fungal community detected in the permafrost showed high indices of diversity, richness and dominance, although these varied between the sampling locations. The use of a metabarcoding approach revealed the presence of DNA of a complex fungal assemblage in the permafrost of the South Shetland Islands including taxa with a range of ecological functions among which were multiple animal, human and plant pathogenic fungi. Further studies are required to determine whether the taxa identified are present in the form of viable cells or propagules and which might be released from melting permafrost to other Antarctic habitats and potentially dispersed more widely.

Identification and Isolation Pattern of Globisporangium spp. from a Sanionia Moss Colony in Ny-Ålesund, Spitsbergen Is., Norway from 2006 to 2018

Globisporangium spp. are soil-inhabiting oomycetes distributed worldwide, including in polar regions. Some species of the genus are known as important plant pathogens. This study aimed to clarify the species construction of Globisporangium spp. and their long-term isolation pattern in Sanionia moss in Ny-Ålesund, Spitsbergen Is., Norway. Globisporangium spp. were isolated at two-year intervals between 2006 and 2018 at a Sanionia moss colony, Ny-Ålesund, Spitsbergen Is., Norway. The isolates were obtained by using three agar media and were identified based on sequences of the rDNA-ITS region and cultural characteristics. Most of the Globisporangium isolates obtained during the survey were identified into six species. All six species were grown at 0 °C on an agar plate and used to infect Sanionia moss at 4 and/or 10 °C under an in vitro inoculation test. The total isolation frequency of Globisporangium gradually decreased throughout the survey period. The isolation frequency varied among the six species, and four of the species that showed a high frequency in 2006 were rarely isolated after 2016. The results suggested that Globisporangium inhabiting Sanionia moss in Ny-Ålesund has a unique composition of species and that most of the species reduced their population over the recent decade.

Ecological succession of fungal and bacterial communities in Antarctic mosses affected by a fairy ring disease

We evaluated fungal and bacterial diversity in an established moss carpet on King George Island, Antarctica, affected by 'fairy ring' disease using metabarcoding. A total of 127 fungal and 706 bacterial taxa were assigned. Ascomycota dominated the fungal assemblages, followed by Basidiomycota, Rozellomycota, Chytridiomycota, Mortierellomycota and Monoblepharomycota. The fungal community displayed high indices of diversity, richness and dominance, which increased from healthy through infected to dead moss samples. A range of fungal taxa were more abundant in dead rather than healthy or fairy ring moss samples. Bacterial diversity and richness were greatest in healthy moss and least within the infected fairy ring. The dominant prokaryotic phyla were Actinobacteriota, Proteobacteria, Bacteroidota and Cyanobacteria. Cyanophyceae sp., whilst consistently dominant, were less abundant in fairy ring samples. Our data confirmed the presence and abundance of a range of plant pathogenic fungi, supporting the hypothesis that the disease is linked with multiple fungal taxa. Further studies are required to characterise the interactions between plant pathogenic fungi and their host Antarctic mosses. Monitoring the dynamics of mutualist, phytopathogenic and decomposer microorganisms associated with moss carpets may provide bioindicators of moss health.

Fungi Present in Antarctic Deep-Sea Sediments Assessed Using DNA Metabarcoding

We assessed fungal diversity in deep-sea sediments obtained from different depths in the Southern Ocean using the internal transcribed spacer 2 (ITS2) region of nuclear ribosomal DNA by metabarcoding through high-throughput sequencing (HTS). We detected 655,991 DNA reads representing 263 fungal amplicon sequence variants (ASVs), dominated by Ascomycota, Basidiomycota, Mortierellomycota, Mucoromycota, Chytridiomycota and Rozellomycota, confirming that deep-sea sediments can represent a hotspot of fungal diversity in Antarctica. The community diversity detected included 17 dominant fungal ASVs, 62 intermediate and 213 rare. The dominant fungi included taxa of Mortierella, Penicillium, Cladosporium, Pseudogymnoascus, Phaeosphaeria and Torula. Despite the extreme conditions of the Southern Ocean benthos, the total fungal community detected in these marine sediments displayed high indices of diversity and richness, and moderate dominance, which varied between the different depths sampled. The highest diversity indices were obtained in sediments from 550 m and 250 m depths. Only 49 ASVs (18.63%) were detected at all the depths sampled, while 16 ASVs were detected only in the deepest sediment sampled at 1463 m. Based on sequence identities, the fungal community included some globally distributed taxa, primarily recorded otherwise from terrestrial environments, suggesting transport from these to deep marine sediments. The assigned taxa included symbionts, decomposers and plant-, animal- and human-pathogenic fungi, suggesting that deep-sea sediments host a complex fungal diversity, although metabarcoding does not itself confirm that living or viable organisms are present.

Diversity of fungal DNA in lake sediments on Vega Island, north-east Antarctic Peninsula assessed using DNA metabarcoding

We assessed the diversity of fungal DNA present in sediments of three lakes on Vega Island, north-east Antarctic Peninsula using metabarcoding through high-throughput sequencing (HTS). A total of 640,902 fungal DNA reads were detected, which were assigned to 224 taxa of the phyla Ascomycota, Rozellomycota, Basidiomycota, Chytridiomycota and Mortierellomycota, in rank order of abundance. The most abundant genera were Pseudogymnoascus, Penicillium and Mortierella. However, a majority (423,508, 66%) of the reads, representing by 43 ASVs, could only be assigned at higher taxonomic levels and may represent taxa not currently included in the sequence databases used or be new or previously unreported taxa present in Antarctic lakes. The three lakes were characterized by high sequence diversity, richness, and moderate dominance indices. The ASVs were dominated by psychrotolerant and cosmopolitan cold-adapted Ascomycota, Basidiomycota and Mortierellomycota commonly reported in Antarctic environments. However, other taxa detected included unidentified members of Rozellomycota and Chytridiomycota species not previously reported in Antarctic lakes. The assigned diversity was composed mainly of taxa recognized as decomposers and pathogens of plants and invertebrates.

Assessment of fungal diversity present in lakes of Maritime Antarctica using DNA metabarcoding: a temporal microcosm experiment

We evaluated the fungal diversity in two lakes on the South Shetland Islands, using DNA metabarcoding through high-throughput sequencing (HTS). A microcosm experiment was deployed for two consecutive years in lakes on Deception and King George islands to capture potential decomposer freshwater fungi. Analyses of the baits revealed 258,326 DNA reads distributed in 34 fungal taxa of the phyla Ascomycota, Basidiomycota, Mortierellomycota, Chytridiomycota and Rozellomycota. Tetracladium marchalianum, Tetracladium sp., Rozellomycota sp., Fungal sp. 1 and Fungal sp. 2 were the most common taxa detected. However, the majority of the communities comprised intermediate and rare taxa. Both fungal communities displayed moderate indices of diversity, richness and dominance. Only six taxa were detected in both lakes, including the most dominant T. marchalianum and Tetracladium sp. The high numbers of reads of the known aquatic saprotrophic hyphomycetes T. marchalianum and Tetracladium sp. in the baits suggest that these fungi may digest organic material in Antarctic lakes, releasing available carbon and nutrients to the other aquatic organisms present in the complex lake food web. Our data confirm that the use of cotton baits together with HTS approaches can be appropriate to study the diversity of resident freshwater fungi present in Antarctic lakes.

DNA metabarcoding uncovers fungal diversity in soils of protected and non-protected areas on Deception Island, Antarctica

We assessed soil fungal diversity at two sites on Deception Island, South Shetland Islands, Antarctica using DNA metabarcoding analysis. The first site was a relatively undisturbed area, and the second was much more heavily impacted by research and tourism. We detected 346 fungal amplicon sequence variants dominated by the phyla Ascomycota, Basidiomycota, Mortierellomycota and Chytridiomycota. We also detected taxa belonging to the rare phyla Mucoromycota and Rozellomycota, which have been difficult to detect in Antarctica by traditional isolation methods. Cladosporium sp., Pseudogymnoascus roseus, Leotiomycetes sp. 2, Penicillium sp., Mortierella sp. 1, Mortierella sp. 2, Pseudogymnoascus appendiculatus and Pseudogymnoascus sp. were the most dominant fungi. In addition, 440,153 of the total of 1,214,875 reads detected could be classified only at the level of Fungi. In both sampling areas the DNA of opportunistic, phytopathogenic and symbiotic fungi were detected, which might have been introduced by human activities, transported by birds or wind, and/or represent resident fungi not previously reported from Antarctica. Further long-term studies are required to elucidate how biological colonization in the island may be affected by climatic changes and/or other anthropogenic influences.

DNA metabarcoding of fungal diversity in air and snow of Livingston Island, South Shetland Islands, Antarctica

We assessed fungal diversity present in air and freshly deposited snow samples obtained from Livingston Island, Antarctica, using DNA metabarcoding through high throughput sequencing (HTS). A total of 740 m3 of air were pumped through a 0.22 µm membrane. Snow obtained shortly after deposition was kept at room temperature and yielded 3.760 L of water, which was filtered using Sterivex membranes of 0.22 µm mesh size. The total DNA present was extracted and sequenced. We detected 171 fungal amplicon sequence variants (ASVs), 70 from the air and 142 from the snow. They were dominated by the phyla Ascomycota, Basidiomycota, Mortierellomycota and Mucoromycota. Pseudogymnoascus, Cladosporium, Mortierella and Penicillium sp. were the most dominant ASVs detected in the air in rank order. In snow, Cladosporium, Pseudogymnoascus, Penicillium, Meyerozyma, Lecidea, Malassezia, Hanseniaspora, Austroplaca, Mortierella, Rhodotorula, Penicillium, Thelebolus, Aspergillus, Poaceicola, Glarea and Lecanora were the dominant ASVs present. In general, the two fungal assemblages displayed high diversity, richness, and dominance indices, with the assemblage found in snow having the highest diversity indices. Of the total fungal ASVs detected, 29 were only present in the air sample and 101 in the snow sample, with only 41 present in both samples; however, when only the dominant taxa from both samples were compared none occurred only in the air and, among the rare portion, 26 taxa occurred in both air and snow. Application of HTS revealed the presence of a more diverse fungal community in the air and snow of Livingston Island in comparison with studies using traditional isolation methods. The assemblages were dominated by cold-adapted and cosmopolitan fungal taxa, including members of the genera Pseudogymnoascus, Malassezia and Rhodotorula, which include some taxa reported as opportunistic. Our results support the hypothesis that the presence of microbiota in the airspora indicates the possibility of dispersal around Antarctica in the air column. However, further aeromycology studies are required to understand the dynamics of fungal dispersal within and beyond Antarctica.

Diversity and distribution of cultivable fungi present in acid sulphate soils in chronosequence under para-periglacial conditions in King George Island, Antarctica

We recovered 85 fungal isolates from the acid sulphate soils in chronosequence under para-periglacial conditions in King George Island, Antarctica. Thirty-two taxa belonging to the phylum Ascomycota, Basidiomycota and Mortierellomycota were identified. Mortierella amoeboidea, Mortierella sp. 2, Mortierella sp. 3, Penicillium sp. 2 and Penicillium sp. 3 dominated the sulphite soils. Despite the multi-extreme physic-chemical conditions of the sulphate soils (low pH, variable content of macro and micronutrients and organic matter), the fungal assemblages exhibited moderate diversity indices, which ranged according to the degree of soil development. Soils with more weathered and, consequently, with highest values of organic carbon shelter the most diverse fungal assemblages, which can be associated with the occurrence of sulphurisation and sulphide oxidation. Different taxa of Mortierella and Penicillium displayed broad pH (3-9) and temperature (5-35 °C) plasticity. The multi-extreme sulphite soils of Antarctica revealed the presence of moderate fungal diversity comprising cold cosmopolitan and psychrophilic endemic taxa. Among these, Mortierella and Penicillium, known to survive in extreme conditions such as low temperature and available organic matter, low pH and high concentrations of metals, might represent interesting techniques to be used in biotechnological processes such as bioleaching in metallurgy and phosphate solubilisation in agriculture.