Integrated assessment of bioplastic materials effects on microbial communities and macroinvertebrate model, Mytilus galloprovincialis, in marine ecosystems

The increasing use of biopolymer derivatives raises concerns about their actual environmental sustainability, which remains insufficiently understood. In this study, we adopted an integrated approach combining microbial and ecotoxicological perspectives to evaluate their impact in marine ecosystems. We investigated the plastisphere composition of conventional petroleum-based High Density Polyethylene (HDPE) and polyhydroxyalkanoates (PHA), polyhydroxybutyric acid (PHB), and polylactic acid (PLLA) scaffolds after 60 days of exposition in marine ecosystem or microcosm, by high throughput metagenomics 16S rRNA gene sequencing and culture dependent approach. A variation in terms of composition and abundance of plastisphere, between petroleum-derived and bio-based degradable scaffolds, was observed. A high abundance of Proteobacteria was detected in all polymers, with Alpha and Gamma Proteobacteria dominant. At the genera level, high abundance of sequences assigned to hydrocarbon-degrading bacteria (i.e. Oleibacter, Labrenzia, Alcanivorax) was detected in biopolymeric plastic compared to petroleum-based plastic. To link microbial colonization and material degradation with biological effects on marine fauna, the impact of biopolymer-derived micro- and nanoparticles on the mussel Mytilus galloprovincialis was assessed. Both in vitro and in vivo assays demonstrated immune system activation through phagocytosis and encapsulation, while in vivo exposures influenced several biomarkers (phagocytosis, haemocyte density, lysozyme, glutathione peroxidase, phenoloxidase, alkaline phosphatase, esterase), suggesting potential detrimental effects after 72 h. By bridging microbial ecology with immunological responses in a bioindicator species, this multidisciplinary study provides novel insights into the complex ecological footprint of biodegradable plastics in marine environments.