Federating young researchers in microbial ecotoxicology: EcotoxicoMicYR 2021, the first international webinar organized for and by young microbial ecotoxicology researchers.

The EcotoxicoMicYR group was initially composed of 4 Ph.D. students and 4 post-doctoral researchers. In brief, the EcotoxicoMicYR webinar took place three Monday afternoons in a row from November 22 to December 6, 2021. These three half-day webinars reached a success beyond our expectations with 25 countries and 41 presentations. Keynote lectures were delivered by Dr Fabio Roldan (Pontificia Universidad Javeriana, Colombia), Dr Belinda Ferrari (The University of New South Wales, Australia), and Dr Ahmed Tlili (Eawag, Switzerland). Their presentations provided an insight on latest research developments in the microbial ecotoxicology field and highlighted their specific contribution to this discipline. Twenty-two oral presentations and 16 pre-recorded presentations were diffused.

Graphene-Based Nanomaterials Modulate Internal Biofilm Interactions and Microbial Diversity.

Graphene-based nanomaterials (GBMs), such as graphene oxide (GO) and reduced graphene oxide (rGO), possess unique properties triggering high expectations for the development of new technological applications and are forecasted to be produced at industrial-scale. This raises the question of potential adverse outcomes on living organisms and especially toward microorganisms constituting the basis of the trophic chain in ecosystems. However, investigations on GBMs toxicity were performed on various microorganisms using single species that are helpful to determine toxicity mechanisms but fail to predict the consequences of the observed effects at a larger organization scale. Thus, this study focuses on the ecotoxicological assessment of GO and rGO toward a biofilm composed of the diatom Nitzschia palea associated to a bacterial consortium. After 48 and 144 h of exposure to these GBMs at 0, 0.1, 1, and 10 mg.L-1, their effects on the diatom physiology, the structure, and the metabolism of bacterial communities were measured through the use of flow cytometry, 16S amplicon sequencing, and Biolog ecoplates, respectively. The exposure to both of these GBMs stimulated the diatom growth. Besides, GO exerted strong bacterial growth inhibition as from 1 mg.L-1, influenced the taxonomic composition of diatom-associated bacterial consortium, and increased transiently the bacterial activity related to carbon cycling, with weak toxicity toward the diatom. On the contrary, rGO was shown to exert a weaker toxicity toward the bacterial consortium, whereas it influenced more strongly the diatom physiology. When compared to the results from the literature using single species tests, our study suggests that diatoms benefited from diatom-bacteria interactions and that the biofilm was able to maintain or recover its carbon-related metabolic activities when exposed to GBMs.