Cytotoxic effect and mechanism of nano-sized polystyrene degraded by Rhodococcus ruber C208

Microbial biodegradation has emerged as a promising solution for environmental issues involving petrochemical-based plastics. However, the altered physicochemical properties of nanoplastics (NPs) induced by biodegradation and their effects on cellular behavior are unclear. Here, we generated NPs (bPS(r)s) using polystyrene (PS) and Rhodococcus ruber C208 (R. ruber C208) to assess changes in physicochemical properties and cytotoxic effects of bPS(r)s in keratinocytes. Compared with PS NPs, the biodegradation of PS using R. ruber C208 induced a decrease in particle size (408.2 to 324.2 nm), extant extracellular polymeric substances, changes in shape and functional groups, surface charge alteration, and enhancement of particle dispersion. Especially, irregular and bumpy surface with disintegration of PS structure was examined in bPS(r). The resulting physicochemical changes in bPS(r)s significantly increased cytotoxicity. This led to three times higher intracellular reactive oxygen species generation in keratinocytes (SOD2 gene expression), and reduced cell proliferation to about 83% of that of PS NPs at the concentration of 1.5 μg/mL. Keratinocytes after bPS(r) treatment also showed upregulated inflammation-related gene (IL-6 and TNF-α) expression compared to that in PS NPs. Overall, our findings suggest new features and methods for future studies on the effect of biodegradable NPs.