The important role of sponges in carbon and nitrogen cycling in a deep-sea biological hotspot

Deep-sea sponge grounds are hotspots of biodiversity, harbouring thriving ecosystems in the otherwise barren deep sea. It remains unknown how these sponge grounds survive in this food-limited environment. Here, we unravel how sponges and their associated fauna sustain themselves by identifying their food sources and food-web interactions using bulk and compound-specific stable isotope analysis of amino and fatty acids. We found that sponges with a high microbial abundance had an isotopic composition resembling organisms at the base of the food web, suggesting that they are able to use dissolved resources that are generally inaccessible to animals. In contrast, low microbial abundance sponges had a bulk isotopic composition that resembles a predator at the top of a food web, which appears to be the result of very efficient recycling pathways that are so far unknown. The compound-specific-isotope analysis, however, positioned low-microbial abundance sponges with other filter-feeding fauna. Furthermore, fatty-acid analysis confirmed transfer of sponge-derived organic material to the otherwise food-limited associated fauna. Through this subsidy, sponges are key to the sustenance of thriving deep-sea ecosystems and might have, due to their ubiquitous abundance, a global impact on biogeochemical cycles. Read the free Plain Language Summary for this article on the Journal blog

Exoerythrocytic Plasmodium Parasites Secrete a Cysteine Protease Inhibitor Involved in Sporozoite Invasion and Capable of Blocking Cell Death of Host Hepatocytes

Plasmodium parasites must control cysteine protease activity that is critical for hepatocyte invasion by sporozoites, liver stage development, host cell survival and merozoite liberation. Here we show that exoerythrocytic P. berghei parasites express a potent cysteine protease inhibitor (PbICP, P. berghei inhibitor of cysteine proteases). We provide evidence that it has an important function in sporozoite invasion and is capable of blocking hepatocyte cell death. Pre-incubation with specific anti-PbICP antiserum significantly decreased the ability of sporozoites to infect hepatocytes and expression of PbICP in mammalian cells protects them against peroxide- and camptothecin-induced cell death. PbICP is secreted by sporozoites prior to and after hepatocyte invasion, localizes to the parasitophorous vacuole as well as to the parasite cytoplasm in the schizont stage and is released into the host cell cytoplasm at the end of the liver stage. Like its homolog falstatin/PfICP in P. falciparum, PbICP consists of a classical N-terminal signal peptide, a long N-terminal extension region and a chagasin-like C-terminal domain. In exoerythrocytic parasites, PbICP is posttranslationally processed, leading to liberation of the C-terminal chagasin-like domain. Biochemical analysis has revealed that both full-length PbICP and the truncated C-terminal domain are very potent inhibitors of cathepsin L-like host and parasite cysteine proteases. The results presented in this study suggest that the inhibitor plays an important role in sporozoite invasion of host cells and in parasite survival during liver stage development by inhibiting host cell proteases involved in programmed cell death

Data for: Fate of intertidal microphytobenthos nitrogen under enhanced nutrient availability: Evidence for a shift in the pool of retained nitrogen revealed through 15N-labeling

Data supporting a pulse-chase study of labeled 15N (ammonium) into sandy intertidal sediment that then underwent nutrient enrichment. The goal was to see how nutrient enrichment affected the fate and processing of the labeled N taken up by MPB.THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

Short-term fate of intertidal microphytobenthos carbon under enhanced nutrient availability: a ¹³C pulse-chase experiment

Shallow coastal waters in many regions are subject to nutrient enrichment. Microphytobenthos (MPB) can account for much of the carbon (C) fixation in these environments, depending on the depth of the water column, but the effect of enhanced nutrient availability on the processing and fate of MPB-derived C (MPB-C) is relatively unknown. In this study, MPB was labeled (stable isotope enrichment) in situ using 13C-sodium bicarbonate. The processing and fate of the newly fixed MPB-C was then traced using ex situ incubations over 3.5 days under different concentrations of nutrients (NH4+ and PO43−: ambient, 2 ×  ambient, 5 ×  ambient, and 10 ×  ambient). After 3.5 days, sediments incubated with increased nutrient concentrations (amended treatments) had increased loss of 13C from sediment organic matter (OM) as a portion of initial uptake (95 % remaining in ambient vs. 79–93 % for amended treatments) and less 13C in MPB (52 % ambient, 26–49 % amended), most likely reflecting increased turnover of MPB-derived C supporting increased production of extracellular enzymes and storage products. Loss of MPB-derived C to the water column via dissolved organic C (DOC) was minimal regardless of treatment (0.4–0.6 %). Loss due to respiration was more substantial, with effluxes of dissolved inorganic C (DIC) increasing with additional nutrient availability (4 % ambient, 6.6–19.8 % amended). These shifts resulted in a decreased turnover time for algal C (419 days ambient, 134–199 days amended). This suggests that nutrient enrichment of estuaries may ultimately lead to decreased retention of carbon within MPB-dominated sediments

Departmental Honors Advisor

In this thesis we argue that content distribution in the face of censorship is an appropriate and feasible application of active networking. In the face of a determined and powerful adversary, every fixed protocol can become known and subsequently monitored, blocked, or its member nodes identified and attacked. Rapid and diverse protocol change is key to allowing information to continue to flow. Typically, decentralized protocol evolution is also an important aspect in providing censor-resistance for publishing networks. These goals can be achieved with the help of active networking techniques, by allowing new protocol implementations, in the form of mobile code, to spread throughout the network. A programmable overlay network can provide protocol change and decentralized protocol evolution. Such a system, however, will need to take steps to ensure that programmability does not present excessive security threats to the network. Runtime isolation, protocol confidence ratings, encryption, and resource control are vital in this respect. We have prototyped such a system as an extension to Freenet, a storage and retrieval system whose goals include censor resistance and anonymity for informa-tion publishers and consumers. Our prototype implements many of the mechanisms discussed in this thesis, indicating that our proposed ideas are feasible to imple-ment. i

The important role of sponges in carbon and nitrogen cycling in a deep‐sea biological hotspot

Deep-sea sponge grounds are hotspots of biodiversity, harboring thriving ecosystems in the otherwise barren deep sea. It remains unknown how these sponge grounds survive in this food-limited environment.2. Here, we unravel how sponges and their associated fauna sustain themselves by identifying their food sources and food-web interactions using bulk and compound-specific stable isotope analysis of amino and fatty acids.3. We found that sponges with a high microbial abundance had an isotopic composition resembling organisms at the base of the food web, suggesting that they are able to use dissolved resources that are generally inaccessible to animals. In contrast, low microbial abundance sponges had a bulk isotopic composition that resembles a predator at the top of a food web, which appears to be the result of very efficient recycling pathways that are so far unknown. The compound-specific-isotope analysis, however, positioned low-microbial abundance sponges with other filter-feeding fauna. Furthermore, fatty-acid analysis confirmed transfer of sponge-derived organic material to the otherwise food-limited associated fauna.4. Through this subsidy, sponges are key to the sustenance of thriving deep-sea ecosystems and might have, due to their ubiquitous abundance, a global impact on biogeochemical cycles