Compound-specific delta N-15 analyses of amino acids for trophic level estimation from indigenous and invasive freshwater amphipods

Invasion of non-native species in freshwater ecosystems often alters the indigenous macroinvertebrate community and food web structure by changing the resource availability. One of these species is the invasive amphipodDikerogammarus villosus, whose impact by predation, especially on coexisting amphipods, is still under debate. In this study, we aim to apply compound-specific stable isotope analysis of amino acid delta N-15, which is the state-of-the-art approach for marine systems to estimate trophic positions, (1) to calculate beta values (i.e., the differences in delta N-15 values of trophic and source amino acids in primary producer) for freshwater systems, based on field samples of freshwater primary consumers (i.e., mussels) from the River Rhine, and (2) use these beta values in a case study to calculate the trophic position of the invasiveD. villosusin comparison with coexisting indigenous and non-native amphipod species from the river Alb sampled in 2013 and river Speyerbach sampled in 2014, two tributaries of the River Rhine, Central Europe. Our results show that our freshwater beta values calculated for six combinations of trophic and source amino acids were lower by between approximately 0.85 parts per thousand and 5.67 parts per thousand than those found for marine animals in previous studies. This highlights that more attention is needed on the variability of the natural differences in beta values between ecosystems. By using the freshwater beta values, we showed that the trophic position ofD. villosusis comparable to those of coexisting amphipod species. These findings confirm thatD. villosushas a flexible and omnivorous feeding strategy like other amphipod species, and suggest that predation is not the main responsible factor for the impact ofD. villosuson other species

An RNA replicon system to investigate promising inhibitors of feline coronavirus.

FIPV is of great significance in the cat population around the world, causing 0.3%-1.4% of feline deaths in veterinary practices (2). As there are neither effective preventive measures nor approved treatment options available, there is an urgent need to identify antiviral drugs against FIPV. Our FCoV replicon system provides a valuable tool for drug discovery in vitro. Due to the lack of cell culture systems for serotype I FCoVs (the serotype most prevalent in the feline population) (2), a different system is needed to study these viruses. A viral replicon system is a valuable tool for studying FCoVs. Overall, our results demonstrate the utility of the serotype I feline coronavirus replicon system for antiviral screening as well as to study this virus in general. We propose several compounds representing promising candidates for future clinical trials and ultimately with the potential to save cats suffering from FIP

Microbial community composition and trophic role along a marked salinity gradient in Laguna Puilar, Salar de Atacama, Chile

The geological, hydrological and microbiological features of the Salar de Atacama, the most extensive evaporitic sedimentary basin in the Atacama Desert of northern Chile, have been extensively studied. In contrast, relatively little attention has been paid to the composition and roles of microbial communities in hypersaline lakes which are a unique feature in the Salar. In the present study biochemical, chemical and molecular biological tools were used to determine the composition and roles of microbial communities in water, microbial mats and sediments along a marked salinity gradient in Laguna Puilar which is located in the Los Flamencos National Reserve. The bacterial communities at the sampling sites were dominated by members of the phyla Bacteroidetes, Chloroflexi, Cyanobacteria and Proteobacteria. Stable isotope and fatty acid analyses revealed marked variability in the composition of microbial mats at different sampling sites both horizontally (at different sites) and vertically (in the different layers). The Laguna Puilar was shown to be a microbially dominated ecosystem in which more than 60% of the fatty acids at particular sites are of bacterial origin. Our pioneering studies also suggest that the energy budgets of avian consumers (three flamingo species) and dominant invertebrates (amphipods and gastropods) use minerals as a source of energy and nutrients. Overall, the results of this study support the view that the Salar de Atacama is a heterogeneous and fragile ecosystem where small changes in environmental conditions may alter the balance of microbial communities with possible consequences at different trophic levels