Polyethylene microbeads induce transcriptional responses with tissue-dependent patterns in the mussel Mytilus galloprovincialis

Plastics are one of the most ubiquitous and conspicuous environmental pollution threats accumulating in natural habitats worldwide. In the ocean, as a result of the actions of sunlight, wind and waves, plastic items are fragmented into microplastics, which are consumed by primary consumers such as filter-feeders, with detrimental consequences to these organisms. Despite the known harmful effects of microplastics, few data are available on their effects on marine invertebrates at the molecular level. The present study evaluates the expression of 12 genes associated with cellular stress, immune response and metabolism on four tissues (gills, digestive gland, haemolymph and mantle) of Mytilus galloprovincialis, after an acute (24 h) exposure to a concentration of 1.5E+7 microbeads of polyethylene per litre (ranging from 1 to 50 μm in size). Analysis showed up-regulation of genes relative to carbon metabolism, oxidative stress, immune response and apoptosis, in the mantle and digestive gland, while a global down-regulation of genes involve in carbon metabolism was observed in the haemolymph and gills. Altogether these results suggest disruptive and tissue-dependent effects on major biological processes following a short exposure to microplastics in M. galloprovincialis. This study provides the first evidence that ingestion of microbeads of polyethylene by filter-feeders induces changes in a tissue-dependent manner at the transcriptome level.