Structural properties and microbial diversity of the biofilm colonizing plastic substrates in Terra Nova Bay (Antarctica).

Microbial colonization on plastic polymers has been extensively explored, however the temporal dynamics of biofilm community in Antarctic environments are almost unknown. As a contribute to fill this knowledge gap, the structural characteristics and microbial diversity of the biofilm associated with polyvinyl chloride (PVC) and polyethylene (PE) panels submerged at 5 m of depth and collected after 3, 9 and 12 months were investigated in four coastal sites of the Ross Sea. Additional panels placed at 5 and 20 m were retrieved after 12 months. Chemical characterization was performed by FTIR-ATR and Raman (through Surface-Enhanced Raman Scattering, SERS) spectroscopy. Bacterial community composition was quantified at a single cell level by Catalyzed Reporter Deposition Fluorescence In Situ Hybridization (CARD-FISH) and Confocal Laser Scanning Microscopy (CLSM); microbial diversity was assessed by 16S rRNA gene sequencing. This multidisciplinary approach has provided new insights into microbial community dynamics during biofouling process, shedding light on the biofilm diversity and temporal succession on plastic substrates in the Ross Sea. Significant differences between free-living and microbial biofilm communities were found, with a more consolidated and structured community composition on PVC compared to PE. Spectral features ascribable to tyrosine, polysaccharides, nucleic acids and lipids characterized the PVC-associated biofilms. Pseudomonadota (among Gamma-proteobacteria) and Alpha-proteobacteria dominated the microbial biofilm community. Interestingly, in Road Bay, close to the Italian "Mario Zucchelli" research station, the biofilm growth - already observed during summer season, after 3 months of submersion - continued afterwards leading to a massive microbial abundance at the end of winter (after 12 months). After 3 months, higher percentages of Gamma-proteobacteria in Road Bay than in the not-impacted site were found. These observations lead us to hypothesize that in this site microbial fouling developed during the first 3 months could serve as a starter pioneering community stimulating the successive growth during winter.

Global biochemical profiling of fast-growing Antarctic bacteria isolated from meltwater ponds by high-throughput FTIR spectroscopy.

Fourier transform infrared (FTIR) spectroscopy is a biophysical technique used for non-destructive biochemical profiling of biological samples. It can provide comprehensive information about the total cellular biochemical profile of microbial cells. In this study, FTIR spectroscopy was used to perform biochemical characterization of twenty-nine bacterial strains isolated from the Antarctic meltwater ponds. The bacteria were grown on two forms of brain heart infusion (BHI) medium: agar at six different temperatures (4, 10, 18, 25, 30, and 37°C) and on broth at 18°C. Multivariate data analysis approaches such as principal component analysis (PCA) and correlation analysis were used to study the difference in biochemical profiles induced by the cultivation conditions. The observed results indicated a strong correlation between FTIR spectra and the phylogenetic relationships among the studied bacteria. The most accurate taxonomy-aligned clustering was achieved with bacteria cultivated on agar. Cultivation on two forms of BHI medium provided biochemically different bacterial biomass. The impact of temperature on the total cellular biochemical profile of the studied bacteria was species-specific, however, similarly for all bacteria, lipid spectral region was the least affected while polysaccharide region was the most affected by different temperatures. The biggest temperature-triggered changes of the cell chemistry were detected for bacteria with a wide temperature tolerance such Pseudomonas lundensis strains and Acinetobacter lwoffii BIM B-1558.

Fiocruz in Antarctica - health and environmental surveillance facing the challenges of the 21st century.

FioAntar, FIOCRUZ's research project in Antarctica, is based on the One Health approach. FioAntar aims to generate relevant information that will help reduce the risk of future pandemics and improve the search for chemical compounds and new biological molecules. After four expeditions to Antarctica under the scope of PROANTAR, Fiocruz has identified Influenza H11N2 virus in environmental fecal samples, as well as Histoplasma capsulatum and Bacillus cereus in soil samples. In addition, in a prospective virome analysis from different lakes in the South Shetland Islands, six viral orders were described, supporting future research related to the biodiversity and viral ecology in this extreme ecosystem. Our findings of environmental pathogens of public health importance are a warning about the urgency of establishing a surveillance agenda on zoonoses in Antarctica due to the imminent risks that ongoing environmental and climate changes impose on human health across the planet. FioAntar strives to establish a comprehensive surveillance program across Antarctica, monitoring circulation of pathogens with the potential to transcend continent boundaries, thereby mitigating potential spread. For Fiocruz, Antarctica signifies a new frontier, teeming with opportunities to explore novel techniques, refine established methodologies, and cultivate invaluable knowledge.

MEDUSA: Marine benthic Ecological Data from Underwater imagery Surveys of sub-Antarctic Crozet environments.

Inscribed on the UNESCO World Heritage list, the sub-Antarctic Crozet archipelago is located in a region facing significant environmental changes impacting a poorly known marine biodiversity. Underwater imagery constitutes a valuable non-invasive approach for gathering ecological data and improving our knowledge of ecosystems' vulnerability. We here compiled two datasets, encompassing 17 video-imagery surveys of Crozet nearshore environments conducted in 2021 and 2022 at two sites of Ile de la Possession: Baie du Marin and Crique du Sphinx. Faunal abundance and algal cover data related to each survey are also provided. A total of 755 images were analysed, comprising 52 faunal and 14 algal taxa identified in 2021, as well as 45 faunal and 14 algal taxa identified in 2022. Video-transects were performed in shallow waters by scuba divers using a GoPro®HERO7 multiple camera set-up, and in deeper waters using a remotely operated vehicle. These data provide a first baseline for biodiversity and ecosystem studies, and for monitoring the long-term dynamics of Crozet benthic habitats facing natural and anthropogenic disturbances.

Resistance to freezing conditions of endemic Antarctic polychaetes is enhanced by cryoprotective proteins produced by their microbiome.

The microbiome plays a key role in the health of all metazoans. Whether and how the microbiome favors the adaptation processes of organisms to extreme conditions, such as those of Antarctica, which are incompatible with most metazoans, is still unknown. We investigated the microbiome of three endemic and widespread species of Antarctic polychaetes: Leitoscoloplos geminus, Aphelochaeta palmeri, and Aglaophamus trissophyllus. We report here that these invertebrates contain a stable bacterial core dominated by Meiothermus and Anoxybacillus, equipped with a versatile genetic makeup and a unique portfolio of proteins useful for coping with extremely cold conditions as revealed by pangenomic and metaproteomic analyses. The close phylosymbiosis between Meiothermus and Anoxybacillus and these Antarctic polychaetes indicates a connection with their hosts that started in the past to support holobiont adaptation to the Antarctic Ocean. The wide suite of bacterial cryoprotective proteins found in Antarctic polychaetes may be useful for the development of nature-based biotechnological applications.

Biotechnological potential of psychrotolerant methylobacteria isolated from biotopes of Antarctic oases.

Ten strains of psychrotolerant methylotrophic bacteria were isolated from the samples collected in Larsemann and Bunger Hills (Antarctica). Most of the isolates are assigned to the genus Pseudomonas, representatives of the genera Janthinobacterium, Massilia, Methylotenera and Flavobacterium were also found. Majority of isolates were able to grow on a wide range of sugars, methylamines and other substrates. Optimal growth temperatures for the isolated strains varied from 6 °C to 28 °C. The optimal concentration of NaCl was 0.5-2.0%. The optimal pH values of the medium were 6-7. It was found that three strains synthesized indole-3-acetic acid on a medium with L-tryptophan reaching 11-12 µg/ml. The values of intracellular carbohydrates in several strains exceeded 50 µg/ml. Presence of calcium-dependent and lanthanum-dependent methanol dehydrogenase have been shown for some isolates. Strains xBan7, xBan20, xBan37, xBan49, xPrg27, xPrg48, xPrg51 showed the presence of free amino acids. Bioprospection of Earth cryosphere for such microorganisms has a potential in biotechnology.

Enzymes and biosurfactants of industrial interest produced by culturable fungi present in sediments of Boeckella Lake, Hope Bay, north-east Antarctic Peninsula.

This study characterized cultivable fungi present in sediments obtained from Boeckella Lake, Hope Bay, in the north-east of the Antarctic Peninsula, and evaluated their production of enzymes and biosurfactants of potential industrial interest. A total of 116 fungal isolates were obtained, which were classified into 16 genera within the phyla Ascomycota, Basidiomycota and Mortierellomycota, in rank. The most abundant genera of filamentous fungi included Pseudogymnoascus, Pseudeurotium and Antarctomyces; for yeasts, Thelebolales and Naganishia taxa were dominant. Overall, the lake sediments exhibited high fungal diversity and moderate richness and dominance. The enzymes esterase, cellulase and protease were the most abundantly produced by these fungi. Ramgea cf. ozimecii, Holtermanniella wattica, Leucosporidium creatinivorum, Leucosporidium sp., Mrakia blollopis, Naganishia sp. and Phenoliferia sp. displayed enzymatic index > 2. Fourteen isolates of filamentous fungi demonstrated an Emulsification Index 24% (EI24%) ≥ 50%; among them, three isolates of A. psychrotrophicus showed an EI24% > 80%. Boeckella Lake itself is in the process of drying out due to the impact of regional climate change, and may be lost completely in approaching decades, therefore hosts a threatened community of cultivable fungi that produce important biomolecules with potential application in biotechnological processes.

Little evidence of inbreeding depression for birth mass, survival and growth in Antarctic fur seal pups.

Inbreeding depression, the loss of offspring fitness due to consanguineous mating, is generally detrimental for individual performance and population viability. We investigated inbreeding effects in a declining population of Antarctic fur seals (Arctocephalus gazella) at Bird Island, South Georgia. Here, localised warming has reduced the availability of the seal's staple diet, Antarctic krill, leading to a temporal increase in the strength of selection against inbred offspring, which are increasingly failing to recruit into the adult breeding population. However, it remains unclear whether selection operates before or after nutritional independence at weaning. We therefore used microsatellite data from 885 pups and their mothers, and SNP array data from 98 mother-offspring pairs, to quantify the effects of individual and maternal inbreeding on three important neonatal fitness traits: birth mass, survival and growth. We did not find any clear or consistent effects of offspring or maternal inbreeding on any of these traits. This suggests that selection filters inbred individuals out of the population as juveniles during the time window between weaning and recruitment. Our study brings into focus a poorly understood life-history stage and emphasises the importance of understanding the ecology and threats facing juvenile pinnipeds.

Genome-resolved metagenomics reveals diverse taxa and metabolic complexity in Antarctic lake microbial structures.

Lake Untersee, a lake in Antarctica that is perennially covered with ice, is home to unique microbial structures that are not lithified. We have evaluated the structure of the community and its metabolic potential across the pigmented upper layers and the sediment-enriched deeper layers in these pinnacle and cone-shaped microbial structures using metagenomics. These microbial structures are inhabited by distinct communities. The upper layers of the cone-shaped structures have a higher abundance of the cyanobacterial MAG Microcoleus, while the pinnacle-shaped structures have a higher abundance of Elainellacea MAG. This suggests that cyanobacteria influence the morphologies of the mats. We identified stark contrasts in the composition of the community and its metabolic potential between the upper and lower layers of the mat. The upper layers of the mat, which receive light, have an increased abundance of photosynthetic pathways. In contrast, the lower layer has an increased abundance of heterotrophic pathways. Our results also showed that Lake Untersee is the first Antarctic lake with a substantial presence of ammonia-oxidizing Nitrospiracea and amoA genes. The genomic capacity for recycling biological molecules was prevalent across metagenome-assembled genomes (MAGs) that cover 19 phyla. This highlights the importance of nutrient scavenging in ultra-oligotrophic environments. Overall, our study provides new insights into the formation of microbial structures and the potential metabolic complexity of Antarctic laminated microbial mats. These mats are important environments for biodiversity that drives biogeochemical cycling in polar deserts.

Kinetic and dynamical properties of truncated hemoglobins of the Antarctic bacterium Pseudoalteromonas haloplanktis TAC125.

Due to the low temperature, the Antarctic marine environment is challenging for protein functioning. Cold-adapted organisms have evolved proteins endowed with higher flexibility and lower stability in comparison to their thermophilic homologs, resulting in enhanced reaction rates at low temperatures. The Antarctic bacterium Pseudoalteromonas haloplanktis TAC125 (PhTAC125) genome is one of the few examples of coexistence of multiple hemoglobin genes encoding, among others, two constitutively transcribed 2/2 hemoglobins (2/2Hbs), also named truncated Hbs (TrHbs), belonging to the Group II (or O), annotated as PSHAa0030 and PSHAa2217. In this work, we describe the ligand binding kinetics and their interrelationship with the dynamical properties of globin Ph-2/2HbO-2217 by combining experimental and computational approaches and implementing a new computational method to retrieve information from molecular dynamic trajectories. We show that our approach allows us to identify docking sites within the protein matrix that are potentially able to transiently accommodate ligands and migration pathways connecting them. Consistently with ligand rebinding studies, our modeling suggests that the distal heme pocket is connected to the solvent through a low energy barrier, while inner cavities play only a minor role in modulating rebinding kinetics.

Prospecting bioactivity in Antarctic algae: A review of extracts, isolated compounds and their effects.

Algae and its metabolites have been a popular subject of research in numerous fields over the years. Various reviews have been written on algal bioactive components, but a specific focus on Antarctic-derived algae is seldom reviewed. Due to the extreme climate conditions of Antarctica, it is hypothesized that the acclimatized algae may have given rise to a new set of bioactive compounds as a result of adaptation. Although most studies done on Antarctic algae are based on ecological and physiological studies, as well as in the field of nanomaterial synthesis, some studies point out the potential therapeutic properties of these compounds. As an effort to shed light on a different application of Antarctic algae, this review focuses on evaluating its different medicinal properties, including antimicrobial, anticancer, antioxidative, anti-inflammatory, and skin protective effects.

A circumpolar study of surface zooplankton biodiversity of the Southern Ocean based on eDNA metabarcoding.

Under pressure from climate change and fishing, the Southern Ocean ecosystems have been changing. Zooplankton plays a vital role in the food web of the Southern Ocean and is crucial for maintaining ecosystem stability. Investigating the circumpolar-scale species composition and biodiversity of zooplankton is crucial for ensuring ecosystem-based conservation and management of the Southern Ocean in a changing climate. Here, we utilized eDNA metabarcoding to assess the biodiversity of zooplankton in the surface seawater surrounding the Antarctica based on samples collected during two expeditions spanning from 2021 to 2022. The main purpose of this paper is to provide more baseline information about circumpolar zooplankton biodiversity based on the emerging eDNA metabarcoding tool. This comprehensive approach led to the identification of over 300 distinct zooplankton species, forming a diverse community dominated by Jellyfish, Mollusca and Polychaete. Surprisingly, common dominant taxonomic groups such as krill and copepods in the Southern Ocean did not show high relative abundance (reads) in surface seawater. The results of redundancy analysis (RDA) and correlation analysis highlighted that water temperature and chlorophyll a had the most significant impact on the reads and diversity of zooplankton. Notably, the influence of water temperature on zooplankton seemed to be primarily indirect, potentially mediated by its effects on primary productivity. Increasing in primary production might lead to lower zooplankton biodiversity in the Southern Ocean in future. This research underscores the effectiveness of eDNA metabarcoding as a valuable tool for monitoring zooplankton diversity in open seas. Given the ongoing changes in temperature, sea ice extent and their impact on primary production, our findings lay a crucial foundation for using eDNA techniques to establish long-term biodiversity monitoring programs across extensive marine ecosystems in the future.

Regional differences in the effects of various Stokes drifts on the cooling of the marine environment under different wave conditions.

The WAVEWATCHIII model is employed to simulate Stokes drift, utilizing four distinct schemes integrated into the SBPOM circulation model. Deviations between simulated values and observations from the Optimum Interpolation Sea Surface Temperature (OISST) dataset unveil significant variations, particularly in regions characterized by pronounced swell. The northern hemisphere exhibits the highest deviations, reaching up to 0.3 °C during the March-April-May (MAM) and December-January-February (DJF) periods, while the Antarctic Circumpolar Current (ACC) consistently displays smaller deviations of approximately 0.1 °C. Deviations from Argo buoy measurements hover around 0.1 °C, except in the northern hemisphere where they escalate to approximately 1.5 °C. A comparative analysis of simulation results and Argo buoy measurements reveals an increasing deviation trend with a higher proportion of swell in specific sea areas, particularly evident in simulations utilizing approximate parameterization schemes. Notably, the Phillips profile scheme exhibits optimal performance, while the monochromatic profile scheme peaks with a simulated deviation of 0.13 °C. In contrast, the wave spectrum profile scheme consistently demonstrates applicability across diverse wave conditions and accurately captures the mixed layer at various depths. This study highlights the importance of the coupled WAVEWATCHIII-SBPOM model in accurately modeling future ocean conditions, providing valuable insight into the field of environmental science.

Exposure to nanoplastics and nanomaterials either single and combined affects the gill-associated microbiome of the Antarctic soft-shelled clam Laternula elliptica.

Nanoplastics and engineering nanomaterials (ENMs) are contaminants of emerging concern (CECs), increasingly being detected in the marine environment and recognized as a potential threat for marine biota at the global level including in polar areas. Few studies have assessed the impact of these anthropogenic nanoparticles in the microbiome of marine invertebrates, however combined exposure resembling natural scenarios has been overlooked. The present study aimed to evaluate the single and combined effects of polystyrene nanoparticles (PS NP) as proxy for nanoplastics and nanoscale titanium dioxide (nano-TiO2) on the prokaryotic communities associated with the gill tissue of the Antarctic soft-shell clam Laternula elliptica, a keystone species of marine benthos Wild-caught specimens were exposed to two environmentally relevant concentrations of carboxylated PS NP (PS-COOH NP, ∼62 nm size) and nano-TiO2 (Aeroxide P25, ∼25 nm) as 5 and 50 µg/L either single and combined for 96h in a semi-static condition.Our findings show a shift in microbiome composition in gills of soft-shell clams exposed to PS NP and nano-TiO2 either alone and in combination with a decrease in the relative abundance of OTU1 (Spirochaetaceae). In addition, an increase of gammaproteobacterial OTUs affiliated to MBAE14 and Methylophagaceae (involved in ammonia denitrification and associated with low-quality water), and the OTU Colwellia rossensis (previously recorded in polluted waters) was observed. Our results suggest that nanoplastics and nano-TiO2 alone and in combination induce alterations in microbiome composition by promoting the increase of negative taxa over beneficial ones in the gills of the Antarctic soft-shell clam. An increase of two low abundance OTUs in PS-COOH NPs exposed clams was also observed. A predicted gene function analysis revealed that sugar, lipid, protein and DNA metabolism were the main functions affected by either PS-COOH NP and nano-TiO2 exposure. The molecular functions involved in the altered affiliated OTUs are novel for nano-CEC exposures.

Comparing trophic position estimates using bulk and compound specific stable isotope analyses: applying new approaches to mackerel icefish Champsocephalus gunnari.

Quantifying the tropic position (TP) of an animal species is key to understanding its ecosystem function. While both bulk and compound-specific analyses of stable isotopes are widely used for this purpose, few studies have assessed the consistency between and within such approaches. Champsocephalus gunnari is a specialist teleost that predates almost exclusively on Antarctic krill Euphausia superba. This well-known and nearly constant trophic relationship makes C. gunnari particularly suitable for assessing consistency between TP methods under field conditions. In the present work, we produced and compared TP estimates for C. gunnari and its main prey using a standard bulk and two amino acid-specific stable isotope approaches (CSI-AA). One based on the difference between glutamate and phenylalanine (TPGlx-Phe), and the other on the proline-phenylalanine difference (TPPro-Phe). To do that, samples from C. gunnari, E. superba and four other pelagic invertebrate and fish species, all potential prey for C.gunnari, were collected off the South Orkney Islands between January and March 2019, analyzed using standard isotopic ratio mass spectrometry methods and interpreted following a Bayesian approach. Median estimates (CI95%) for C. gunnari were similar between TPbulk (3.6; CI95%: 3.0-4.8) and TPGlx-Phe(3.4; CI95%:3.2-3.6), and lower for TPPro-Phe (3.1; CI95%:3.0-3.3). TP differences between C. gunnari and E. superba were 1.4, 1.1 and 1.2, all compatible with expectations from the monospecific diet of this predator (ΔTP=1). While these results suggest greater accuracy for Glx-Phe and Pro-Phe, differences observed between both CSI-AA approaches suggests these methods may require further validation before becoming a standard tool for trophic ecology.

History of Diversification and Adaptation from North to South Revealed by Genomic Data: Guanacos from the Desert to Sub-Antarctica.

The increased availability of quality genomic data has greatly improved the scope and resolution of our understanding of the recent evolutionary history of wild species adapted to extreme environments and their susceptibility to anthropogenic impacts. The guanaco (Lama guanicoe), the largest wild ungulate in South America, is a good example. The guanaco is well adapted to a wide range of habitats, including the Sechura Desert, the high Andes Mountains to the north, and the extreme temperatures and conditions of Navarino Island to the south. Guanacos also have a long history of overexploitation by humans. To assess the evolutionary impact of these challenging habitats on the genomic diversity, we analyzed 38 genomes (∼10 to 16×) throughout their extensive latitudinal distribution from the Sechura and Atacama Desert to southward into Tierra del Fuego Island. These included analyses of patterns of unique differentiation in the north and geographic region further south with admixture among L. g. cacsilensis and L. g. guanicoe. Our findings provide new insights on the divergence of the subspecies ∼800,000 yr BP and document two divergent demographic trajectories and to the initial expansion of guanaco into the more southern portions of the Atacama Desert. Patagonian guanacos have experienced contemporary reductions in effective population sizes, likely the consequence of anthropogenic impacts. The lowest levels of genetic diversity corresponded to their northern and western limits of distribution and some varying degrees of genetic differentiation. Adaptive genomic diversity was strongly linked with environmental variables and was linked with colonization toward the south followed by adaptation.

Transcriptional and structural analysis of non-specific lipid transfer proteins modulated by fungal endophytes in Antarctic plants under drought.

Lipid transfer proteins (LTPs) play crucial roles in various biological processes in plants, such as pollen tube adhesion, phospholipid transfer, cuticle synthesis, and response to abiotic stress. While a few members of the non-specific LTPs (nsLTPs) have been identified, their structural characteristics remain largely unexplored. Given the observed improvement in the performance of Antarctic plants facing water deficit when associated with fungal endophytes, this study aimed to assess the role of these symbiotic organisms in the transcriptional modulation of putative nsLTPs. The study focused on identifying and characterizing two nsLTP in the Antarctic plant Colobanthus quitensis that exhibit responsiveness to drought stress. Furthermore, we investigated the influence of Antarctic endophytic fungi on the expression profiles of these nsLTPs, as these fungi have been known to enhance plant physiological and biochemical performance under water deficit conditions. Through 3D modeling, docking, and molecular dynamics simulations with different substrates, the conducted structural and ligand-protein interaction analyses showed that differentially expressed nsLTPs displayed the ability to interact with various ligands, with a higher affinity towards palmitoyl-CoA. Overall, our findings suggest a regulatory mechanism for the expression of these two nsLTPs in Colobanthus quitensis under drought stress, further modulated by the presence of endophytic fungi.

Peptide Toxins from Antarctica: The Nemertean Predator and Scavenger Parborlasia corrugatus (McIntosh, 1876).

Peptide toxins from marine invertebrates have found use as drugs and in biotechnological applications. Many marine habitats, however, remain underexplored for natural products, and the Southern Ocean is among them. Here, we report toxins from one of the top predators in Antarctic waters: the nemertean worm Parborlasia corrugatus (McIntosh, 1876). Transcriptome mining revealed a total of ten putative toxins with a cysteine pattern similar to that of alpha nemertides, four nemertide-beta-type sequences, and two novel full-length parborlysins. Nemertean worms express toxins in the epidermal mucus. Here, the expression was determined by liquid chromatography combined with mass spectrometry. The findings include a new type of nemertide, 8750 Da, containing eight cysteines. In addition, we report the presence of six cysteine-containing peptides. The toxicity of tissue extracts and mucus fractions was tested in an Artemia assay. Notably, significant activity was observed both in tissue and the high-molecular-weight mucus fraction, as well as in a parborlysin fraction. Membrane permeabilization experiments display the membranolytic activity of some peptides, most prominently the parborlysin fraction, with an estimated EC50 of 70 nM.

Metabolomics analysis of physicochemical properties associated with freshness degradation in frozen Antarctic krill (Euphausia superba).

This study aimed to determine the effect of different frozen temperatures during storage on the quality of Antarctic krill (Euphausia superba) and assess the change at the metabolite level via a combination of physicochemical property analysis, liquid chromatography-tandem mass spectrometry (LC-MS) based non-targeted metabolomics profiling. Regarding samples stored at -20 °C, the expressions of 7055 metabolites were elevated, while 2313 were downregulated. Lipids and lipid molecules had the highest proportion of differential metabolites. A total of 432 discriminatory metabolites with Kyoto Encyclopedia of Genes and Genomes (KEGG) IDs was obtained. We also observed that the concentrations of differential bitter free amino acids (FAAs) and oxidation products of arachidonic and linoleic acid increased. Moreover, as the storage temperature increased, the freshness, umami, and sweetness components were considerably reduced. Furthermore, results indicated that the color, pH and water-holding capacity (WHC) were potential indicators of quality deterioration, while inosinic acid was a probable biomarker for umami degradation of frozen Antarctic krill. In conclusion, this study demonstrates that storage at lower temperatures can be beneficial for maintaining the freshness of Antarctic krill from macro and micro perspectives.

Biosynthesis of photostable CdS quantum dots by UV-resistant psychrotolerant bacteria isolated from Union Glacier, Antarctica.

BACKGROUND: Quantum Dots (QDs) are fluorescent nanoparticles with exceptional optical and optoelectronic properties, finding widespread utility in diverse industrial applications. Presently, chemically synthesized QDs are employed in solar cells, bioimaging, and various technological domains. However, many applications demand QDs with prolonged lifespans under conditions of high-energy radiation. Over the past decade, microbial biosynthesis of nanomaterials has emerged as a sustainable and cost-effective process. In this context, the utilization of extremophile microorganisms for synthesizing QDs with unique properties has recently been reported. RESULTS: In this study, UV-resistant bacteria were isolated from one of the most extreme environments in Antarctica, Union Glacier at the Ellsworth Mountains. Bacterial isolates, identified through 16 S sequencing, belong to the genera Rhodococcus, Pseudarthrobacter, and Arthrobacter. Notably, Rhodococcus sp. (EXRC-4 A-4), Pseudarthrobacter sp. (RC-2-3), and Arthrobacter sp. (EH-1B-1) tolerate UV-C radiation doses ≥ 120 J/m². Isolated UV-resistant bacteria biosynthesized CdS QDs with fluorescence intensities 4 to 8 times higher than those biosynthesized by E. coli, a mesophilic organism tolerating low doses of UV radiation. Transmission electron microscopy (TEM) analysis determined QD sizes ranging from 6 to 23 nm, and Fourier-transform infrared (FTIR) analysis demonstrated the presence of biomolecules. QDs produced by UV-resistant Antarctic bacteria exhibit high photostability after exposure to UV-B radiation, particularly in comparison to those biosynthesized by E. coli. Interestingly, red fluorescence-emitting QDs biosynthesized by Rhodococcus sp. (EXRC-4 A-4) and Arthrobacter sp. (EH-1B-1) increased their fluorescence emission after irradiation. Analysis of methylene blue degradation after exposure to irradiated QDs biosynthesized by UV-resistant bacteria, indicates that the QDs transfer their electrons to O2 for the formation of reactive oxygen species (ROS) at different levels. CONCLUSIONS: UV-resistant Antarctic bacteria represent a novel alternative for the sustainable generation of nanostructures with increased radiation tolerance-two characteristics favoring their potential application in technologies requiring continuous exposure to high-energy radiation.