Bénédicte Sohm

We address here the physicochemical surface properties of C. vulgaris, including electrostatics and hydrophobicity, at various biological organisation scales using soft surface electrokinetics, proton titration and chemical force spectroscopy.

Despite the involvement of several serine hydrolases (SHs) in the metabolism of xenobiotics such as dibutyl phthalate (DBP), no study has focused on mapping this enzyme class in zebrafish, a model organism frequently used in ecotoxicology. Here, we survey and identify active SHs in zebrafish larvae and search for biological markers of SH type after exposure to DBP. Zebrafish were exposed to 0, 5, and 100 µg/L DBP from 4 to 120 h post-fertilization. A significant decrease in vitellogenin expression level of about 2-fold compared to the control was found in larvae exposed to 100 µg/L DBP for 120 h. The first comprehensive profiling of active SHs in zebrafish proteome was achieved with an activity-based protein profiling (ABPP) approach. Among 49 SHs identified with high confidence, one was the carboxypeptidase ctsa overexpressed in larvae exposed to 100 µg/L DBP for 120 h. To the best of our knowledge, this is the first time that a carboxypeptidase has been identified as deregulated following exposure to DBP. The overall results indicate that targeted proteomics approaches, such as ABPP, can, therefore, be an asset for understanding the mechanism of action related to xenobiotics in ecotoxicology.

Progressive rare earth element (REE) enrichment in aquatic environments worldwide and their resulting anthropogenic anomalies have highlighted the need for a better understanding of their biological effects, with a special emphasis on microbial cells since they play a crucial role in good ecosystem functioning. Therefore, the primary aim of this work was to achieve simultaneous characterization of the 16 REE toxicity effects on the growth kinetics of the commonly found Gram-negative bacterium E. coli (BW25113 strain). Bacterial growth curve modelling showed hormetic effects in the presence of REEs, while EC₅₀ determination (in the mid-log phase) indicated that the four HREEs from Er to Lu in addition to Y were the most toxic metals (EC₅₀ in the range of 8.3 to 3 μM), just after Sc (EC₅₀ of 1.1 μM). Additional subcellular parameter assessment revealed cell membrane lipid peroxidation as well as enhanced membrane depolarization and permeability in the presence of La, Gd, or Yb as representatives of LREEs and HREEs. These subcellular effects appeared to be more intense with Gd and Yb compared with La-exposed cells, in relation to the overall higher toxicity potential reported for HREEs on bacterial growth. Also, the cellular ATP production decreased after REE exposure at their EC₅₀. Finally, these results emphasize the importance of growth kinetic consideration as well as the complexity of REE biological effect mechanisms towards bacteria.

Dreissenids are established model species for ecological and ecotoxicological studies, since they are sessile and filter feeder organisms and reflect in situ freshwater quality. Despite this strong interest for hydrosystem biomonitoring, omics data are still scarce. In the present study, we achieved full de novo assembly transcriptomes of digestive glands to gain insight into Dreissena polymorpha and D. rostriformis bugensis molecular knowledge. Transcriptomes were obtained by Illumina RNA sequencing of seventy-nine organisms issued from fifteen populations inhabiting sites that exhibits multiple freshwater contamination levels and different hydrosystem topographies (open or closed systems). Based on a recent de novo assembly algorithm, we carried out a complete, quality-checked and annotated transcriptomes. The power of the present study lies in the completeness of transcriptomes gathering multipopulational organisms sequencing and its full availability through an open access interface that gives a friendly and ready-to-use access to data. The use of such data for proteogenomic and targeted biological pathway investigations purpose is promising as they are first full transcriptomes for this two Dreissena species.

Mutations in the rfa operon leading to severely truncated lipopolysaccharide (LPS) structures are associated with pleiotropic effects on bacterial cells, which in turn generates a complex phenotype termed deep-rough. Literature reports distinct behavior of these mutants in terms of susceptibility to bacteriophages and to several antibacterial substances. There is so far a critical lack of understanding of such peculiar structure-reactivity relationships mainly due to a paucity of thorough biophysical and biochemical characterizations of the surfaces of these mutants. In the current study, the biophysicochemical features of the envelopes of Escherichia coli deep-rough mutants are identified from the molecular to the single cell and population levels using a suite of complementary techniques, namely microelectrophoresis, Atomic Force Microscopy (AFM) and Isobaric Tag for Relative and Absolute Quantitation (iTRAQ) for quantitative proteomics. Electrokinetic, nanomechanical and proteomic analyses evidence enhanced mutant membrane destabilization/permeability, and differentiated abundances of outer membrane proteins involved in the susceptibility phenotypes of LPS-truncated mutants towards bacteriophages, antimicrobial peptides and hydrophobic antibiotics. In particular, inner-core LPS altered mutants exhibit the most pronounced heterogeneity in the spatial distribution of their Young modulus and stiffness, which is symptomatic of deep damages on cell envelope likely to mediate phage infection process and antibiotic action.

The BH3-only class of Bcl-2 family proteins triggers mitochondrial apoptosis. Several mechanisms are used to restrain the pro-apoptotic activity of these proteins. Dynein light chain (DYNLL) 1 and 2 has been proposed to negatively regulate the activity of Bim and Bmf, respectively, and the Bim–DYNLL1 interaction leads to the formation of large protein complexes on mitochondria. Here we found that Bim and Bmf interact with both isoforms of DYNLL (DYNLL1 and DYNLL2). DYNLL1/2 not only induced homo-dimerization of Bim and Bmf but also led to the formation of ternary complexes (Bim–DYNLL–Bmf), both in cell-free and in cellular systems. DYNLL-induced oligomerization stabilized Bmf in cultured cells and inhibited its degradation by the ubiquitin-independent 20S proteasome in a cell-free system. Surprisingly, overexpression of wild-type Bmf but not of a DYNLL-binding-deficient mutant induced degradation of endogenous Bim in different cell lines, but both variants sensitized to apoptosis. Mutant Bmf incapable of interacting with anti-apoptotic Bcl-2 proteins and of inducing apoptosis still caused Bim degradation. These results suggest that Bmf overexpression-induced Bim degradation is not due to the displacement of Bim from anti-apoptotic Bcl-2 proteins but a direct consequence of the modulation of Bim–DYNLL association. A peptide derived from the DYNLL-binding domain of Bim also led to the degradation of Bim as well as of its preferred binding partner Mcl-1. Thus DYNLL regulates the mitochondrial pathway of apoptosis by determining the stability of Bmf, Bim, and Mcl-1 proteins.

Zinc oxide (ZnO) nanoparticles are commonly used in sunscreens for their UV-filtering properties. Their growing use can lead to their release into ecosystems, raising question about their toxicity. Effects of these engineered nanomaterials (ENMs) on cyanobacteria, which are important primary producers involved in many biogeochemical cycles, are unknown. In this study, we investigated by several complementary approaches the toxicological effects of two marketed ZnO-ENMs (coated and uncoated) on the model cyanobacteria Synechococcus elongatus PCC 7942. It was shown that despite the rapid adsorption of ENMs on cell surface, toxicity is mainly due to labile Zn released by ENMs. Zn dissipates cell membrane potential necessary for both photosynthesis and respiration, and induces oxidative stress leading to lipid peroxidation and DNA damages. It leads to global downregulation of photosystems, oxidative phosphorylation, and transcription/translation machineries. This also translates into significant decrease of intracellular ATP content and cell growth inhibition. However, there is no major loss of pigments and even rather an increase in exposed cells compared to controls. A proposed way to reduce the environmental impact of Zn would be the improvement of the coating stability to prevent solubility of ZnO-ENMs.