Development of a metabolite-driven daphnia ecophysiological model

Combined effects of the pesticide spinetoram and the cyanobacterium Microcystis on the water flea Daphnia pulex

Spinetoram is one of the most worldwidely used pesticides for its high insecticidal efficacy and low human toxicity. Following the large usage of spinetoram, the ecotoxicity and environmental risks to aquatic ecosystems have call for urgent study. In the present study, we investigated the combined effects of spinetoram and the harmful alga Microcystis aeruginosa in freshwater, on survival and reproduction of Daphnia pulex. Acute toxicity test of spinetoram resulted in negative effects on survival, with a 48-h LC₅₀ value of 37.71 μg L^-1. Under the long-time exposure to environmentally relevant concentrations (0.18 and 0.35 μg L^-1) of spinetoram and a low composition of Microcystis (30%) in the diet, D. pulex showed both shorter longevity and lower fecundity; the time to first brood also increased. At population level, carrying capacity was highly decreased by spinetoram and Microcystis, whereas a significant decrease of intrinsic growth rate was observed at 0.35 μg L^-1 spinetoram with 30% Microcystis as food. The present study highlighted that pesticide spinetoram had highly toxic effects on D. pulex and could reduce the tolerance of D. pulex to M. aeruginosa, causing great effects on D. pulex population in natural waterbodies.

Selective Amino Acid-Only in Vivo NMR: A Powerful Tool To Follow Stress Processes

In vivo NMR of small 13C-enriched aquatic organisms is developing as a powerful tool to detect and explain toxic stress at the biochemical level. Amino acids are a very important category of metabolites for stress detection as they are involved in the vast majority of stress response pathways. As such, they are a useful proxy for stress detection in general, which could then be a trigger for more in-depth analysis of the metabolome. 1H-13C heteronuclear single quantum coherence (HSQC) is commonly used to provide additional spectral dispersion in vivo and permit metabolite assignment. While some amino acids can be assigned from HSQC, spectral overlap makes monitoring them in vivo challenging. Here, an experiment typically used to study protein structures is adapted for the selective detection of amino acids inside living Daphnia magna (water fleas). All 20 common amino acids can be selectively detected in both extracts and in vivo. By monitoring bisphenol-A exposure, the in vivo amino acid-only approach identified larger fluxes in a greater number of amino acids when compared to published works using extracts from whole organism homogenates. This suggests that amino acid-only NMR of living organisms may be a very sensitive tool in the detection of stress in vivo and is highly complementary to more traditional metabolomics-based methods. The ability of selective NMR experiments to help researchers to "look inside" living organisms and only detect specific molecules of interest is quite profound and paves the way for the future development of additional targeted experiments for in vivo research and monitoring.