In January 2022, gaseous elemental Hg (GEM) concentrations were continuously monitored at Syowa Station on East Ongul Island, located similar to 4 km from the continent on the eastern coast of Lutzow-Holm Bay, to examine atmospheric Hg concentrations during the summer in the southeastern Antarctic region. Atmospheric GEM ranged from 0.36 to 1.83 ng m(-3) average value: 1.01 +/- 0.21 ng m(-3) and increased during the day and decreased at night. While maintaining these diurnal variations, GEM concentrations increased to 1.99 and 1.55 ng m(-3) on January 2-3 and 17-20, 2022, respectively. During both events, the low-pressure system approached the Syowa Station, and the 72 hours backward trajectory analysis revealed that the air mass originated from open water surfaces, implying that Hg evasion from the sea surface increased the atmospheric GEM concentration. To investigate the causes of diurnal variation causes-excluding these two events mentioned-Hg concentrations in the soil [n = 102, 2.61 +/- 3.16 (0.14-19.0) ng g(-1)], snow, glacier, and ice sheet around Syowa Station (n = 19, 0.45-5.60 ng L-1), as well as in the atmosphere on the fast ice around the station (0.54-1.10 ng m(-3)), were measured. The results revealed that sources such as ornithogenic soil from the penguin rookery around the station, open water surfaces, and the gaseous oxidized Hg transported inland by katabatic winds did not contribute to the daytime GEM concentration increases. The cause of the summer diurnal variation at Syowa Station was unidentified and warrants further investigation.

Most species of the genus Mycobacterium are widely distributed in soil and aquatic environments; however, there is limited understanding of their distribution and adaptation to permanently cold environments. Psychrophilic/psychrotolerant bacteria isolated from cold environments represent an important resource that can be used to understand these aspects. Here, we report representative psychrotolerant mycobacteria strains, designated TUM20985T, TUM20983, and TUM20984, from Antarctic soils. Phylogenetic analysis using the 16S rRNA gene and average nucleotide identity confirmed that these three strains belong to the same species, and are most closely related to Mycobacterium hodleri JCM 12141T. These strains are psychrotolerant and grow at 4-25 °C, but not above 30 °C. All three strains exhibited a higher proportion of unsaturated fatty acids compared with closely related species, with C18:1ω9c, C17:1ω8c, C17:0, and C16:0 identified as the major fatty acids. The predominant respiratory quinone was MK-9(H2). Comparative genomic analysis showed potential functional divergence in lipid metabolism genes, and revealed the presence of nitrate reduction and potential methane or ammonia oxidation genes that were absent in closely related species. Based on these findings, we propose that our strains represent a novel species, designated Mycobacterium antarcticum sp. nov., with TUM20985T (RIMD 4000203T = NCTC 15058T) as the type strain.

Climate-driven changes in the abundance, distribution, and migration patterns of forage fish affect the diet composition of seabirds. Decadal climate changes, known as regime shifts, have occurred several times in the Sea of Japan, influencing the food web and leading to shifts in the diet of diving seabird species. To examine whether a long-range surface-feeding species, Streaked Shearwater Calonectris leucomelas, switched diet in response to the 2013/2014 regime shift, we sampled 826 stomach contents from individuals at Awashima Island between 2008 and 2020. They fed mainly on Japanese Anchovy Engraulis japonicus and Bullet Mackerel Auxis rochei, with benthic fish as minor prey, both during the negative and positive phases of the Pacific Decadal Oscillation (PDO) before and after the 2013/2014 regime shift, thus showing no evidence of prey switching. Although fisheries landings of Japanese Anchovy and Bullet Mackerel showed decreasing trends after the 2013/2014 regime shift, with a rise in cold-water Japanese Sardine (Sardinops melanostictus) dominance, this change was not reflected in the shearwater diet. Streaked Shearwater, a highly mobile and adaptable seabird species with an extensive foraging range, maintained a relatively stable diet, even under unpredictable environmental conditions including climate shifts.

Seasonal and inter-annual changes in the diets of seabirds are expected to relate to the abundance and distribution of their prey species. We analyzed the stomach contents of 227 male and female Streaked Shearwater Calonectris leucomelas during the chick-rearing period on Awashima in the Sea of Japan between 2008 and 2013. They fed predominantly on Japanese Anchovy Engraulis japonicus early in the season but changed their diet, consuming increasing numbers of benthic fish species (mainly Gadidae, Sebastidae, and Zoarcidae) later in the season. Being surface feeders, they possibly fed on these benthic species discarded by the trawl fishing boats in intense fishing grounds of both the Pacific and the Sea of Japan. Moreover, the shearwaters also showed sex-specific differences in their diet. Females fed more on anchovies, while males tended to feed more on benthic species, presumably when they fed in the Pacific and the northern part of the Sea of Japan. They fed more on benthic fish in years with high sea surface temperatures (SST), probably due to low availability of epipelagic fish. With the trend of global sea warming, our results indicate the importance of fisheries-related food sources far from the colony for this generalist surface-feeding seabird.

The diversity of bacteria associated with lichens has received increasing attention. However, studies based on next-generation sequencing of microbiomes have not yet been conducted in the Arctic and Subarctic regions. In this study, rock-dwelling lichens belonging to the Umbilicariaceae family were sampled from the Arctic and Subarctic biological zones. The primary research purpose was to undertake a comparative investigation of the bacterial composition and diversity, identify potential indicators, and explore their potential metabolic pathways. 18S rRNA gene sequences of the fungal partner belonging to the genus Umbilicaria (Ascomycota) and the algal partner affiliated with the lineage Trebouxia (Chlorophyta). Comparing Umbilicaria spp. with a previous study in the Antarctic zone, the fungal partners were more inclined to cluster by sampling region. Operational taxonomic units (OTUs) were established based on a predetermined similarity threshold for V3-V4 sequences, which were ascribed to 19 bacterial phyla, and ten of them were consistently present in all samples. The most distinct zonal indicator genera based on OTU frequencies from Arctic and Subarctic lichens were Capsulimonas (Armatimonadota) and Jatrophihabitans (Actinomycota), respectively. Although the Subarctic zone had higher biodiversity and species richness based on alpha-diversity, the beta-diversity showed that the main species of bacterial communities were not significantly different, and the predictions of metabolic pathways based on the bacterial microbiome in lichen samples from the two zones were similar. These findings provide evidence that the geographical and/or bioclimatic environment and the different lichen-forming fungal species mainly and partially influence bacterial microbiomes and metabolic pathways.

The Antarctic terrestrial environment harbors a diverse community of microorganisms, which have adapted to the extreme conditions. The aim of this study was to describe the composition of microbial communities in a diverse range of terrestrial environments (various biocrusts and soils, sands from ephemeral wetlands, biofilms, endolithic and hypolithic communities) in East Antarctica using both molecular and morphological approaches. Amplicon sequencing of the 16S rRNA gene revealed the dominance of Chloroflexi, Cyanobacteria and Firmicutes, while sequencing of the 18S rRNA gene showed the prevalence of Alveolata, Chloroplastida, Metazoa, and Rhizaria. This study also provided a comprehensive assessment of the microphototrophic community revealing a diversity of cyanobacteria and eukaryotic microalgae in various Antarctic terrestrial samples. Filamentous cyanobacteria belonging to the orders Oscillatoriales and Pseudanabaenales dominated prokaryotic community, while members of Trebouxiophyceae were the most abundant representatives of eukaryotes. In addition, the co-occurrence analysis showed a prevalence of positive correlations with bacterial taxa frequently co-occurring together.

We studied Holocene paleolimnological changes inferred from multi-proxy data set of CNS elements, biomarkers and microscopic observation of microalgae and cyanobacteria in sediment cores from Rundvågshetta lakes (Maruwanminami-ike and Maruwan o-ike) in the Soya Coast region of East Antarctica, along with sedimentary facies and AMS 14 C dating. They are discussed with paleoenvironmental changes, transition ages and glacio-isostatic uplift rates in the Soya Coast region and East Antarctica. Ages of the Maruwanminami-ike core (MwS4C-01, length 147 cm) and Maruwan-oike (Mw4C-01, length 226 cm) ranged from 1,230-5,010 cal BP) and 2,240-5,700 cal BP, respectively. Reservoir effects of the Rundvågshetta lakes were very high which may be due to the influence of dead carbon in glacially eroded marine sediments and base rocks. Average sedimentation rates of Lakes Maruwanminami-ike and Maruwan-oike were 0.389 and 0.649 mm/yr, respectively. Crustal uplift rates of Lakes Maruwanminami-ike and Maruwan-oike determined by sedimentary facies, green sulfur bacterial biomarkers and diatoms were estimated to be 8.24 and 8.25 mm/yr, respectively. Coastal marine environment: Maruwanminami-ike (147-72.5 cm, 5,010-2,590 cal BP) and Maruwan-oike (226-47.2 cm, 5,700-3,190 cal BP) were characterized by low biological production with the predominance of diatoms. Transition period of stratified brackish lake environment: Maruwanminami-ike (72.5-65.6 cm, 2,590-2,500 cal BP) and Maruwan-oike (47.2-28.8 cm, 3,190-2,890 cal BP) were characterized by stratified conditions with marine water overlain by freshwater, and a chemocline developed together with an anoxic layer in the bottom of photic zone. Freshwater lake environment of Maruwanminami-ike (65.6-0 cm, 2,500-1,230 cal BP) was characterized by high biological production by cyanobacteria (e.g. Leptolyngbya spp.) and green algae (e.g. Comarium clepsydra) with some contribution of diatoms, while that of Maruwan-oike (28.8-0 cm, 2,890-2,240 cal BP) was very low biological production. The marine to terrestrial transition ages of raised beaches and isolated basins in the Saya Coast region ranged from 970 to 9,290 yr BP with an average of 3,660±1,520 yr BP (standard deviation) suggesting that major warm periods in the region are the middle Holocene. Glacio-isostatic uplift rates of raised basins and isolated basins in the Soya Coast region ranged from 0.19 to 4.40 mm/yr with an average of 2.0 ± 0.92 mm/yr which is similar to East Antarctica. Glacio-isostatic uplift rates of raised beaches are correlated with altitudes with a correlation coefficient of r 2 = 0.724. Increasing crustal uplift rates with altitudes reflect continuous crustal uplifts in the Soya Coast region.

Since the establishment of Syowa Station over six decades ago, the study on the terrestrial bacterial community surrounding the station has been notably lacking and inadequately documented. Using the latest sequencing technology, we revealed the soil bacterial composition from soil samples collected from the surrounding of the station. In doing so, we also assessed the effect of human disturbances brought upon by different activities in the proximity of the station, in contrast to those in less human interference and pristine areas. Our results show that human activities near the main station facilities, especially within the 100-m range, visibly changed the structure and functions of the soil microbial community. Areas with high levels of human disturbances displayed a decrease in both microbial diversity and richness, accompanied by a lower count of unique amplicon sequence variants (ASVs) compared to regions with intermediate and low human disturbances. Moreover, higher proportions of functions related to hydrocarbon degradation were also predicted from samples collected within this area. In contrast, soil microbial communities from intermediate and low human disturbances samples have higher proportions of bacterial groups and functions consistent with those in undisturbed natural habitats.

Schizorhynchia is a group of free-living interstitial flatworms within Kalyptorhynchia, characterized by possessing a split proboscis. To date, only seven species of Schizorhynchia have been recorded from Japan. Here, we describe two new species of schizorhynchs, Proschizorhynchella quadricaudatasp. nov. and Cheliplana izuensissp. nov., based on specimens collected from the intertidal zone of Japanese waters. We also explored the phylogenetic position of the new taxa based on partial sequences of the nuclear 18S rRNA and 28S rRNA genes. Proschizorhynchella quadricaudatasp. nov. is characterized by (i) proboscis lips with a row of glands; (ii) a simple cone-shaped stylet; and (iii) a caudal end with four finger-shaped projections. Cheliplana izuensissp. nov. can be distinguished from its congeners by (i) two strong hooks with bifurcate tips, encircling the distal part of the spiny cirrus; (ii) the fact that the proximal 20% of the cirrus length is unarmed; (iii) proboscis’ sidepieces lacking needles; (iv) paired seminal vesicles; and (v) the presence of a vagina. The phylogenetic analyses support the position of P. quadricaudatasp. nov. within Schizorhynchidae and the position of C. izuensissp. nov. in a clade containing all species of Cheliplana within Cheliplanidae.

Mosses are distributed all over the world including Antarctica. Although Antarctic mosses show active growth in a short summer season under harsh environments such as low temperature, drought and high levels of UV radiation, survival mechanisms for such multiple environmental stresses of Antarctic mosses have not yet been clarified. In the present study, transcriptome analyses were performed using one of the common mosses Bryum pseudotriquetrum grown under an Antarctic field and artificial cultivation conditions. Totally 88 205 contigs were generated by de novo assembly, among which 1377 and 435 genes were significantly up and downregulated, respectively, under Antarctic field conditions compared with artificial cultivation conditions at 15 degrees C. Among the upregulated genes, a number of lipid metabolism-related and oil body formation-related genes were identified. Expression levels of these genes were increased by artificial environmental stress treatments such as low temperature, salt and osmic stress treatments. Consistent with these results, B. pseudotriquetrum grown under Antarctic field conditions contained large amounts of fatty acids, especially alpha-linolenic acid, linolenic acid and arachidonic acid. In addition, proportion of unsaturated fatty acids, which enhance membrane fluidity, to the total fatty acids was also higher in B. pseudotriquetrum grown under Antarctic field conditions. Since lipid accumulation and unsaturation of fatty acids are generally important factors for the acquisition of various environmental stress tolerance in plants, these intracellular physiological and metabolic changes may be responsible for the survival of B. pseudotriquetrum under Antarctic harsh environments. Antarctica has harsh environments including low temperatures, drought and high levels of UV radiation etc. Although several moss species grow in Antarctica, their survival and adaptation mechanisms for such multiple environmental stresses have not yet been known. Here, we performed transcriptome analyses using one of the common mosses B. pseudotriquetrum grown in Antarctica. Our results showed a possibility that lipid accumulation and change in fatty acid composition are major mechanisms for acquiring environmental stress tolerance in Antarctic mosses. In addition, we proposed the importance of on-site analysis for elucidating actual plant environmental responses and stress tolerance mechanisms in nature.

There have been several records in the last 60 years for East Antarctica for Milnesium tardigradum Doyère, 1840 sensu lato, now considered a species complex. During the 56th Japanese Antarctic Research Expedition summer operation (2014-2015), a new tardigrade species in the genus Milnesium Doyère, 1840 was found in an ice-free Innhovde area along Lützow-Holm Bay, Dronning Maud Land, East Antarctica. The new species has aberrant claws with four to seven points on each secondary claw branch, which distinguishes it from other Milnesium species. A male specimen was found in the population and evidence showed that an isolated adult female moulted twice without oviposition. This strongly suggested bisexual reproduction for this population. The new species, Milnesium rastrum sp. nov., is described with its phylogenetic position and a discussion on the reproductive strategies for the harsh environments.

We report the whole-genome sequences of three psychrotolerant Mycolicibacterium strains, TUM20983, TUM20984, and TUM20985, isolated from Antarctic soils. Taxonomic analyses indicate that these strains are putative new species. These genome sequences may provide insight into the cold adaptation mechanisms of Mycolicibacterium spp. through future comparative genomic studies.

Antarctic expeditions have a high risk of participant depression owing to long stays and isolated environments. By quantifying the stress state and changes in biomolecules over time before the onset of depressive symptoms, predictive markers of depression can be explored. Here, we evaluated the psychological changes in 30 participants in the Japanese Antarctic Research Expedition using the Patient Health Questionnaire-9 (PHQ-9). Urinary samples were collected every three months for a year, and comprehensive urinary metabolomic profiles were quantified using liquid chromatography time-of-flight mass spectrometry. Five participants showed major depressive episodes (PHQ-9 ≥ 10) at 12 months. The urinary metabolites between these participants and the 25 unaffected participants were compared at individual metabolite and pathway levels. The individual comparisons showed the most significant differences at 12 months in 14 metabolites, including ornithine and beta-alanine. Data from shorter stays showed less significant differences. In contrast, pathway and enrichment analyses showed the most significant difference at three months and a less significant difference at longer stays. These time transitions of urinary metabolites could help in the development of urinary biomarkers to detect subjects with depressive episodes at an early stage.

Here, we report the complete genome sequence of Polynucleobacter sp. strain TUM22923, isolated from Antarctic lake sediment. This strain has a genome of 1,860,127 bp, comprising 1,848 protein-coding sequences. These sequence data could contribute to the elucidation of genome streamlining and low-temperature adaptation in members of Polynucleobacter, a cosmopolitan group of ultramicrobacteria.

Microbial mats in Antarctica are known to harbor microscopic organisms. Recently, comprehensive studies of the diversity of microbial mats have been conducted using genetic analysis of 16 S rRNA and 18 S rRNA genes. However, the quantitative biological contribution of each microorganism constituting the microbial mats remains unknown. We surveyed microscopic phototrophs and invertebrates in mats sampled from five lakes and one ephemeral wetland on the Soya Coast, East Antarctica. We identified seven taxonomic groups of phototrophs, of which five (Orders Chroococcales, Nostocales, and Oscillatoriales, and Classes Chlorophyceae and Bacillariophyceae) were found at all sites, and three taxonomic groups of invertebrates (Class Bdelloidea, and Phyla Nematoda, Tardigrada). Bdelloidea were the most predominant invertebrate group at all sampling sites. The biomass of the Bdelloidea was 4-10 times higher than the total biomass of the Nematoda and Tardigrada at all sampling sites. The total biomass of all groups identified was higher in the ephemeral wetland than in the lakes. Of the five lakes, Skallen Oike had the highest total biomass. These findings suggest that higher biomasses exist in eutrophic environments (the marine relict lake, Skallen Oike, and an ephemeral wetland) where nutritional carryover or higher nutritional flux is expected. In addition, statistical differences in the community structure among the lakes and the ephemeral wetland could be detected based on the biomass compositions of the taxonomic groups. The community structure of each lake and the wetland was statistically dissimilar, indicating the phototrophs and invertebrates had a unique community structure at each study site.

Increased research attention is being given to bacterial diversity associated with lichens. Rock tripe lichens (Umbilicariaceae) were collected from two distinct Antarctic biological regions, the continental region near the Japanese Antarctic station (Syowa Station) and the maritime Antarctic South Orkney Islands (Signy Island), in order to compare their bacterial floras and potential metabolism. Bulk DNA extracted from the lichen samples was used to amplify the 18S rRNA gene and the V3-V4 region of the 16S rRNA gene, whose amplicons were Sanger- and MiSeq-sequenced, respectively. The fungal and algal partners represented members of the ascomycete genus Umbilicaria and the green algal genus Trebouxia, based on 18S rRNA gene sequences. The V3-V4 sequences were grouped into operational taxonomic units (OTUs), which were assigned to eight bacterial phyla, Acidobacteriota, Actinomyceota, Armatimonadota, Bacteroidota, Cyanobacteria, Deinococcota, Pseudomonadota and the candidate phylum Saccharibacteria (also known as TM7), commonly present in all samples. The OTU floras of the two biological regions were clearly distinct, with regional biomarker genera, such as Mucilaginibacter and Gluconacetobacter, respectively. The OTU-based metabolism analysis predicted higher membrane transport activities in the maritime Antarctic OTUs, probably influenced by the sampling area's warmer maritime climatic setting.

Extreme sexual size dimorphism is one of the most striking phenomena in evolutionary biology. While the origin has been well discussed and some causes have been suggested, the evolutionary history remains unclear. We found a new species of deep-sea scale worm (Annelida: Polynoidae) inside gastropod shells, either empty or occupied by hermit crabs collected at 140-306 m in depth, Mie Prefecture, Japan. This highly specialized habitat, together with the fact that it has never been found free-living, led us to consider the scale worm to be an obligate symbiont. The species is characterized by males being dwarf, with their minute bodies (ca. one-fourth the length of females) always riding on the dorsal side of females, being thus the first case of extreme sexual size dimorphism in scale worms. Based on a detailed morphological, histological, and molecular phylogenetic approach we are here describing a new species, Eunoe issunboushi sp. nov.

The complete genome sequences of Aureimonas sp. strain SA4125 and its native plasmid pSA4125 were determined. The genome sequence comprises 4,968,066 bp, with a GC content of 66.0%, and contains 4,691 coding DNA sequences (CDSs), 3 rRNA operons, and 50 tRNAs. The native plasmid comprises 131,777 bp, with a GC content of 62.3%, and contains 138 CDSs.

Waterborne pathogenic diseases are public health issues, especially for people staying in remote environments, such as Antarctica. After repeated detection of Legionella by PCR from the shower room of Syowa Station, the Japanese Antarctic research station, we wanted to understand the occurrence of waterborne pathogens, especially Legionella, in the station and their potential sources. In this study, we analyzed water and biofilm samples collected from the water facilities of Syowa Station, as well as water samples from surrounding glacier lakes, by 16S rRNA gene-based amplicon sequencing. For Legionella spp., we further attempted to obtain a detailed community structure by using genus-specific primers. The results showed that potentially pathogenic genera were mostly localized in the station, while Legionella spp., Pseudomonas spp., and Mycobacterium spp. were also widely distributed in lakes. Genus-specific analysis of Legionella spp. within the lake environments confirmed the presence of diverse Legionella amplicon sequence variants (ASVs) that were distinctly different from the Legionella ASVs detected in the station. The majority of the Legionella ASVs inhabiting Antarctic lake habitats were phylogenetically distinct from known Legionella species, whereas the ASVs detected in the human-made station tended to contain ASVs highly similar to well-described mesophilic species with human pathogenicity. These data suggest that unexpected Legionella diversity exists in remote Antarctic cold environments and that environmental differences (e.g., temperature) in and around the station affect the community structure.IMPORTANCE We comprehensively examined the localization of potential waterborne pathogens in the Antarctic human-made and natural aquatic environment with special focus on Legionella spp. Some potential pathogenic genera were detected with low relative abundance in the natural environment, but most detections of these genera occurred in the station. Through detailed community analysis of Legionella spp., we revealed that a variety of Legionella spp. was widely distributed in the Antarctic environment and that they were phylogenetically distinct from the described species. This fact indicates that there are still diverse unknown Legionella spp. in Antarctica, and this genus encompasses a greater variety of species in low-temperature environments than is currently known. In contrast, amplicon sequence variants closely related to known Legionella spp. with reported pathogenicity were almost solely localized in the station, suggesting that human-made environments alter the Legionella community.

Culture-independent analysis shows that Legionella spp. inhabit a wide range of low-temperature environments, but to date, no psychrotolerant or psychrophilic strains have been reported. Here, we characterized the first cultivated psychrotolerant representative, designated strain TUM19329T, isolated from an Antarctic lake using a polyphasic approach and comparative genomic analysis. A genome-wide phylogenetic tree indicated that this strain was phylogenetically separate at the species level. Strain TUM19329T shared common physiological traits (e.g., Gram-negative, limited growth on buffered charcoal-yeast extract α-ketoglutarate [BCYEα] agar with l-cysteine requirements) with its relatives, but it also showed psychrotolerant growth properties (e.g., growth at 4°C to 25°C). Moreover, this strain altered its own cellular fatty acid composition to accumulate unsaturated fatty acid at a lower temperature, which may help maintain the cell membrane fluidity. Through comparative genomic analysis, we found that this strain possessed massive mobile genetic elements compared with other species, amounting to up to 17% of the total genes. The majority of the elements were the result of the spread of only a few insertion sequences (ISs), which were spread throughout the genome by a "copy-and-paste" mechanism. Furthermore, we found metabolic genes, such as fatty acid synthesis-related genes, acquired by horizontal gene transfer (HGT). The expansion of ISs and HGT events may play a major role in shaping the phenotype and physiology of this strain. On the basis of the features presented here, we propose a new species-Legionella antarctica sp. nov.-represented by strain TUM19329T (= GTC 22699T = NCTC 14581T). IMPORTANCE This study characterized a unique cultivated representative of the genus Legionella isolated from an Antarctic lake. This psychrotolerant strain had some common properties of known Legionella species but also displayed other characteristics, such as plasticity in fatty acid composition and an enrichment of mobile genes in the genome. These remarkable properties, as well as other factors, may contribute to cold hardiness, and this first cultivated cold-tolerant strain of the genus Legionella may serve as a model bacterium for further studies. It is worth noting that environmentally derived 16S rRNA gene phylotypes closely related to the strain characterized here have been detected from diverse environments outside Antarctica, suggesting a wide distribution of psychrotolerant Legionella bacteria. Our culture- and genome-based findings may accelerate the ongoing studies of the behavior and pathogenicity of Legionella spp., which have been monitored for many years in the context of public health.