Blue mussel (Mytilus edulis L.) exposure to nylon microfibers leads to a shift in digestive gland microbiota

Microplastics are an increasingly prevalent form of pollution in coastal ecosystems. Current research focuses on understanding the impacts of such synthetic particles on the health and functioning of aquatic organisms. Recent studies have shown that invertebrates can accumulate microplastics in their tissue, impacting key functions such as growth, reproduction, feeding activity, and metabolism. Owing to their chemical composition, microplastics accumulating in the digestive tract of animals may alter the diversity and abundance of microbiota. Despite the important implications of such microbiota shifts on digestive ability and fitness, investigations on microplastics as causative agents are so far limited. In this study, we tested the effect of microfibers, on the digestive gland microbiota of the blue mussel Mytilus edulis after a 52-day exposure. Our findings show that exposure to microplastics can alter the composition of the digestive gland microbiota, with significant decreases in the classes of Actinobacteria, Bacteroidia, and significant increases for Alphaproteobacteria and Gammaproteobacteria. Furthermore, an increase in the number of genera containing potential pathogenic species for bivalves, such as Francisella and Vibrio, was detected. This suggests that accumulated microplastics pose a dual threat to filter-feeding organisms and the ecosystem services they provide. Further comparative studies are necessary to establish whether the microbiota shift is linked to the specific chemical composition of microplastics or whether there is an indirect link such as physiological stress resulting from ingestion.