Biofilm exposure to copper: bioaccumulation and effects on fatty acid profiles and micromeiofauna taxonomic composition

International audience

anglais. Periphytic biofilms, fundamental components of aquatic ecosystems, host a wide variety of organisms, including the often overlooked micromeiofauna. These small but essential organisms play a crucial role within biofilms. Despite their ecological importance, the response of micromeiofauna to environmental contaminants such as metals remains poorly understood. Copper, a common industrial pollutant, is essential in trace amounts but toxic at high concentrations. While its effects on primary producers in biofilms are well documented, its effects on micromeiofauna and biofilm fatty acid profiles are not well understood. This study aims to identify possible effects of copper on the biodiversity and taxonomic composition of biofilm micromeiofauna. As a preliminary study, we conducted a microcosm experiment in which we exposed periphytic biofilms to copper at environmental concentrations.Increasing copper bioaccumulation correlates with a decrease in micromeiofaunal abundance at high concentrations, indicating copper toxicity. Copperhad no effect on DHA and EPA, suggesting that trophic relationships did not influence micromeiofaunal abundance. Thus, the reduction in micromeiofaunaseems to be due to a direct toxic effect. Studies on micromeiofauna based on microscopic observations are limited in number and scope due to thetechnical limitations of preserving these organisms. Identification of micromeiofauna requires fresh (live) material, is time-consuming, and requiresmeticulous handling and taxonomic expertise. Metabarcoding is a promising approach to study microbial diversity. Metabarcoding will be performed on our samples using 16S (bacteria), 18S (eukaryotes), COI (proto-metazoans) and ITS (fungi). The comparison of DNA-based community assessment of biofilmorganisms with our microscopic observations and fatty acid profiles will improve our understanding of copper-induced changes in the biofilm matrix.Assessing the relative proportions of algal groups will also help to better interpret our results. These future perspectives will enrich our understanding ofthe effects of copper on the biofilm matrix.