Diversity and enzymatic, biosurfactant and phytotoxic activities of culturable Ascomycota fungi present in marine sediments obtained near the South Shetland Islands, maritime Antarctica

We studied the culturable fungal community recovered from deep marine sediments in the maritime Antarctic, and assessed their capabilities to produce exoenzymes, emulsifiers and metabolites with phytotoxic activity. Sixty-eight Ascomycota fungal isolates were recovered and identified. The most abundant taxon recovered was the yeast Meyerozyma guilliermondii, followed by the filamentous fungi Penicillium chrysogenum, P. cf. palitans, Pseudeurotium cf. bakeri, Thelebolus balaustiformis, Antarctomyces psychrotrophicus and Cladosporium sp. Diversity indices displayed low values overall, with the highest values obtained at shallow depth, decreasing to the deepest location sampled. Only M. guilliermondii and P. cf. palitans were detected in the sediments at all depths sampled, and were the most abundant taxa at all sample sites. The most abundant enzymes detected were proteases, followed by invertases, cellulases, lipases, carrageenases, agarases, pectinases and esterases. Four isolates showed good biosurfactant activity, particularly the endemic species A. psychrotrophicus. Twenty-four isolates of P. cf. palitans displayed strong phytotoxic activities against the models Lactuca sativa and Allium schoenoprasum. The cultivable fungi recovered demonstrated good biosynthetic activity in the production of hydrolytic exoenzymes, biosurfactant molecules and metabolites with phytotoxic activity, reinforcing the importance of documenting the taxonomic, ecological and biotechnological properties of fungi present in deep oceanic sediments of the Southern Ocean.

Elemental and mineralogical characterization of marine sediments and their relationship to sedimentary and oceanographic processes in Central Bransfield Basin

This work consists of the sedimentological, mineralogical, and geochemical characterization of eight marine sediment cores collected in the Central Bransfield Basin, along a transect between the South Shetland Islands to the Antarctic Peninsula and its correlation to the sedimentary and oceanographic processes of the area. A chemical characterization based on X-ray fluorescence dispersive spectrometry was implemented to obtain geochemical data of the marine sediment while the minerals were identified by X-ray diffraction. The study allowed to classify the cores into three groups according to their sediment source and chemical and mineralogical characteristics. The joint assessment of the geochemical and mineralogical signature of the sediment has confirmed that the elemental ratios Ti/Ca and Fe/Ca can be applied as proxies in the reconstitution of the terrigenous contribution to the Central Bransfield Basin if we consider the sedimentary contribution of the volcanic edifices present in the region. The Fe/K ratio associated with the Chemical Index of Alteration reinforced an increase in the degree of weathering near South Shetland Island, which is also pointed out by other authors in studies on climate change mainly in the subantarctic islands. The trend of temperature increase implies the importance of monitoring the region.

Geomorphology of Martel inlet, King George Island, Antarctica: a new interpretation based on multi-resolution topo-bathymetric data

This study investigated the terrestrial and submarine geomorphology and glacial landform records in the Martel inlet (King George Island) using a multi-resolution topobathymetric data based on seismic, multibeam surveys and terrestrial satellite datasets (REMA DEM). Geomorphometric analysis provided glacial landforms and sedimentary processes interpretation. The submarine sector has a mean depth of 143 m, a maximum depth of 398 m, and most of it has a low slope (0°-16°). Steep slopes (>30°) are found along the mid-outer sectors transition area. The continental shelf was divided into inner fjord (49 m depth), middle fjord (119 m), and outer fjord (259 m), based on depth, elevation and slope. The topobathymetric digital model provides evidence of geomorphological contrasts between these zones in the fjord's seafloor and subaerial environments. A prominent morainal bank in the transition between the inner and middle parts marks the limit of a past stationary stage of the Dobrowolski-Goetel ice margin. Streamlined glacial lineations demonstrate an NE-SW past ice flow direction and a wet-based thermal regime. The combined analysis of submarine and subaerial landforms enable the understanding of the former glacier configuration and its deglaciation history.

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.