Carbon sources of Antarctic nematodes as revealed by natural carbon isotope ratios and a pulse-chase experiment

δ13C of nematode communities in 27 sites was analyzed, spanning a large depth range (from 130 to 2,021 m) in five Antarctic regions, and compared to isotopic signatures of sediment organic matter. Sediment organic matter δ13C ranged from −24.4 to −21.9‰ without significant differences between regions, substrate types or depths. Nematode δ13C showed a larger range, from −34.6 to −19.3‰, and was more depleted than sediment organic matter typically by 1‰ and by up to 3‰ in silty substrata. These, and the isotopically heavy meiofauna at some stations, suggest substantial selectivity of some meiofauna for specific components of the sedimenting plankton. However, 13C-depletion in lipids and a potential contribution of chemoautotrophic carbon in the diet of the abundant genus Sabatieria may confound this interpretation. Carbon sources for Antarctic nematodes were also explored by means of an experiment in which the fate of a fresh pulse of labile carbon to the benthos was followed. This organic carbon was remineralized at a rate (11–20 mg C m−2 day−1) comparable to mineralization rates in continental slope sediments. There was no lag between sedimentation and mineralization; uptake by nematodes, however, did show such a lag. Nematodes contributed negligibly to benthic carbon mineralization

Processes driven by the small sized organisms at the water-sediment interface

The small sized organisms including prokaryotes (bacteria and archaea), protozoa and metazoan meiofauna (< 250 µm) are the driving forces for biogeochemical fluxes in surficial deepsea sediments under oxic conditions. The relative proportion of small sized organisms increases along trophic gradients from eutrophy to oligotrophy or from the continental margin towards the mid oceanic deep-sea. They can consume up to 10% of freshly sedimented organic matter per day. The small sized fauna consumes and respires the largest part of organic matter, while macrofauna is instrumental in incorporating fresh detritus into the sediment, structuring the environment and thus facilitating microbial processes. Small organisms, in particular prokaryotes, can adapt to amount and quality of organic matter input. Under nutrient starvation probably a large proportion of the prokaryotic community is dormant and is reactivated during sedimentation events. On time scales of 7–10 days (metabolism) to 2–3 weeks (biomass increase) they can react to pulses of deposition of organic material. However, the history of food supply influences the speed of adaptation and effectiveness of growth. At stations close to continental margins estimates of organic matter input from sediment traps largely disagree with measurements of benthic respiration, carbon turnover or estimates obtained from geochemical modelling. This discrepancy is much smaller at mid-oceanic stations. Lateral inputs from productive shelf seas into the deep-sea are suspected to cause this discrepancy

Isg15 Deficiency and Increased Viral Resistance in Humans but Not Mice

ISG15 is an interferon (IFN)-α/β-induced ubiquitin-like protein. It exists as a free molecule, intracellularly and extracellularly, and conjugated to target proteins. Studies in mice have demonstrated a role for Isg15 in antiviral immunity. By contrast, human ISG15 was shown to have critical immune functions, but not in antiviral immunity. Namely, free extracellular ISG15 is crucial in IFN-γ-dependent antimycobacterial immunity, while free intracellular ISG15 is crucial for USP18-mediated downregulation of IFN-α/β signalling. Here we describe ISG15-deficient patients who display no enhanced susceptibility to viruses in vivo, in stark contrast to Isg15-deficient mice. Furthermore, fibroblasts derived from ISG15-deficient patients display enhanced antiviral protection, and expression of ISG15 attenuates viral resistance to WT control levels. The species-specific gain-of-function in antiviral immunity observed in ISG15 deficiency is explained by the requirement of ISG15 to sustain USP18 levels in humans, a mechanism not operating in mice., ISG15 is a ubiquitin-like protein which has important immune-related functions in mice and humans. Here the authors demonstrate that, unlike in mice, human ISG15 stabilizes UPS18 and that ISG15-deficient human cells are more resistant to viral infection.PubMedWoSScopu