Promoting Biofilm Formation by Serratia marcescens on Three Types of Artificially Aged Microplastics Under Marine Conditions

Bacterial biofilms on different types of microplastics in aquatic environments have become an increasing ecological and public health concern. In this context, this study investigated biofilm formation on virgin and aged microplastics under marine conditions. Serratia marcescens biofilm formation was observed on both virgin and aged polyethylene particles after 7 days, with no significant changes by day 14. Concerning polypropylene microplastics, biofilms developed on aged particles but were not detectable on virgin particles, likely due to interference from the polypropylene red color matching S. marcescens cells. In contrast, expanded polystyrene spheres showed an initial biofilm formation that dissipated by day 14, potentially due to toxic residues from photooxidation, including potential styrene monomers and other chemical additives, inhibiting biofilm persistence. These findings indicate differences in biofilm formation across microplastics types, which may influence microplastic buoyancy and ecological impacts. Thus, microplastic color and additives should be considered in future studies on microplastics biofilm formation and biofouling.