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In polar regions, the microphytobenthos has important ecological functions in shallow-water habitats, such as on top of coastal sediments. This community is dominated by benthic diatoms, which contribute significantly to primary production and biogeochemical cycling while also being an important component of polar food webs. Polar diatoms are able to cope with markedly changing light conditions and prolonged periods of darkness during the polar night in Antarctica. However, the underlying mechanisms are poorly understood. In this study, five strains of Antarctic benthic diatoms were isolated in the field, and the resulting unialgal cultures were identified as four distinct species, of which one is described as a new species, Planothidium wetzelii sp. nov. All four species were thoroughly examined using physiological, cell biological, and biochemical methods over a fully controlled dark period of 3 months. The results showed that the utilization of storage lipids is one of the key mechanisms in Antarctic benthic diatoms to survive the polar night, although different fatty acids were involved in the investigated taxa. In all tested species, the storage lipid content declined significantly, along with an ultrastructurally observable degradation of the chloroplasts. Surprisingly, photosynthetic performance did not change significantly despite chloroplasts decreasing in thylakoid membranes and an increased number of plastoglobules. Thus, a combination of biochemical and cell biological mechanisms allows Antarctic benthic diatoms to survive the polar night. [ABSTRACT FROM AUTHOR]

Krill species are key organisms in the Antarctic food web. Biochemical composition in terms of lipids, proteins, carbohydrates, and fatty acids and its implications for spatial distribution were investigated in specimens of Euphausia superba and Euphausia crystallorophias collected in the Ross Sea and the adjacent Pacific region during an acoustic survey carried out within the framework of the 19th Italian National Program for Research in Antarctica (PNRA) Expedition, to gain insights into their trophic relationships and bioenergetic strategies. In both species, the body biochemical composition (wet) showed a predominance of proteins (62–86%), followed by lipids and carbohydrates, and, among identified lipid classes, the two species did not seem to differ much in fatty acid composition. Results showed the highest dissimilarity in biochemical composition between species relative to differences in latitude (24%) and to inshore/offshore haul (22%). Fatty acid analysis, and particularly PUFA/SFA and 18PUFA/16PUFA ratios, allowed identification of a more pronounced omnivorous kind of diet in E. crystallorophias relative to E. superba. [ABSTRACT FROM AUTHOR]

Antarctica is an ideal analogue for studying the limits of life. Despite severe temperature fluctuations and desiccating conditions, life is commonly found colonizing the structural cavities within Antarctic rocks (i.e., endoliths). Previous studies have speculated that the slow cycling of endoliths in the McMurdo Dry Valleys may be the limit of life on Earth. However, very little is known about the in situ activities of these communities—especially in regions outside the McMurdo Dry Valleys where endoliths are thought to be cycling carbon very slowly (e.g., hundreds of years). Here, we show that East Antarctic endoliths found on nunataks are cycling carbon quickly and are therefore quite active. Through radiocarbon (14C) analyses of the viable cell membrane (as phospholipid-derived fatty acids [PLFA]), we found that the Δ14C composition of these microbial communities was on average predominantly modern, with a few samples signaling older carbon in the system. These findings indicate that endoliths inhabiting inland Antarctic nunataks are cycling carbon on decadal timescales, which support the notion that endoliths in Antarctica are cycling carbon quickly. This work provides new insights into the potential variability of Antarctic endolith activities and demonstrates that, despite the climatic extremes that exist farther inland on the most inhospitable continent on Earth, indigenous life can thrive. [ABSTRACT FROM AUTHOR]

The marine environment supports vast habitats with prodigious biodiversity comprising the largest source of unique bioactive compounds biosynthesized by macro and microorganisms, including seaweeds and their associated fungi. In this context, the interest in studying and characterizing marine natural products has increased in the last years. Among these metabolites, lipids and their derivatives play an important role in the metabolism of marine organisms and are sources of substances with therapeutic properties and biotechnological purposes. In this research, it was investigated the lipid amount present in the algae species Ascoseira mirabilis, Adenocystis utricularis, Desmarestia anceps, Phaeurus antarcticus and in their associated endophytic fungi Aspergillus flavus, Penicillium echinulatum, Microascus croci and Penicillium purpurogenum, respectively. This study was achieved by gas chromatography–mass spectrometry, using a standard methodology to analyze all of the components present in the eight organisms. Fatty acids (FAs) and sterols are among the lipids of the highest concentration in the studied algae and fungi. In general, phytol and fucosterol were the most abundant metabolites in all seaweed, while in endophytic fungi, the FAs (palmitic, linoleic, oleic and stearic acid) and ergosterol appeared in major concentrations. This work contributes to new chemical information on the underexploited biodiversity of macroalgae and endophytic fungi belonging to the Antarctic Peninsula and, furthermore, to increase the possibilities for the discovery of bioactive substances and apply it on biotechnological approaches. [ABSTRACT FROM AUTHOR]

The meroplanktonic larvae of benthic organisms are an important seasonal component of the zooplankton in temperate coastal waters. The larvae of the reef-building polychaete Lanice conchilega contribute up to 15% of the summer zooplankton biomass in the North Sea. Despite their importance for reef maintenance (which positively affects the benthic community), little is known about the trophic ecology of this meroplanktonic larva. Qualitative and quantitative estimates of carbon (C) transfer between trophic levels and of fatty acid (FA)—specific assimilation, biosynthesis, and bioconversion can be obtained by compound-specific stable isotope analysis of FA. The present work tested the hypothesis that the concept of fatty acid trophic markers (FATM), widely used for studies on holoplankton with intermediate to high lipid contents, is also applicable to lipid-poor organisms such as meroplanktonic larvae. The incorporation of isotopically-enriched dietary C by L. conchilega larvae was traced, and lipid assimilation did not follow FA-specific relative availabilities in the diet. Furthermore, FAs that were unavailable in the diet, such as 22:5(n-3), were recorded in L. conchilega, suggesting their bioconversion by the larvae. The results indicate that L. conchilega larvae preferentially assimilate certain FAs and regulate their FA composition (lipid homeostasis) independently of that of their diet. Their quasi-homeostatic response to dietary FA availability could imply that the concept of FATM has limited application in lipid-poor organisms such as L. conchilega larvae. [ABSTRACT FROM AUTHOR]

Filamentous green algae of the genus Zygnema (Zygnematophyceae, Streptophyta) are key components of polar hydro-terrestrial mats where they face various stressors including UV irradiation, freezing, desiccation and osmotic stress. Their vegetative cells can develop into pre-akinetes, i.e. reserve-rich, mature cells. We investigated lipid accumulation and fatty acid (FA) composition upon pre-akinete formation in an Arctic and an Antarctic Zygnema strain using transmission electron microscopy and gas chromatography coupled with mass spectrometry. Pre-akinetes formed after 9 weeks of cultivation in nitrogen-free medium, which was accompanied by massive accumulation of lipid bodies. The composition of FAs was similar in both strains, and a-linolenic acid (C18:3) dominated in young vegetative cells. Pre-akinete formation coincided with a significant change in FA composition. Oleic (C18:1) and linoleic (C18:2) acid increased the most (up to 17- and 8-fold, respectively). Small amounts of long-chain polyunsaturated FAs were also detected, e.g. arachidonic (C20:4) and eicosapentaenoic (C20:5) acid. Pre-akinetes exposed to desiccation at 86% relative humidity were able to recover maximum quantum yield of photosystem II, but desiccation had no major effect on FA composition. The results are discussed with regard to the capability of Zygnema spp. to thrive in extreme conditions. [ABSTRACT FROM AUTHOR]