Combined effects of copper oxide and nickel oxide coated chitosan nanoparticles adsorbed to styrofoam resin beads on hydrothermal vent bacteria

Microplastics are potential carriers of harmful contaminants but their combined effects are largely unknown. It needs intensive monitoring in order to achieve a better understanding of metal-oxide nanoparticles and their dispersion via microplastics such as styrofoam in the aquatic environment. In the present study, an effort was made to provide a preferable perception about the toxic effects of engineered nanoparticles (NPs), namely, copper oxide (CuO NPs), nickel oxide (NiO NPs), copper oxide/chitosan (CuO/CS NPs) and nickel oxide/chitosan (NiO/CS NPs). Characterizations of synthesized NPs included their morphology (SEM and EDX), functional groups (FT-IR) and crystallinity (XRD). Their combined toxic effect after adsorption to styrofoam (SF) was monitored using the hydrothermal vent bacterium Jeotgalicoccus huakuii as a model. This was done by determining MIC (minimum inhibitory concentration) through a resazurin assay measuring ELISA, growth, biofilm inhibition and making a live and dead assay. Results revealed that at high concentrations (60 mg/10 mL) of CuO, CuO/CS NPs and 60 mg of SF adsorbed CuO and CuO/CS NPs inhibited the growth of J. huakuii. However, NPs rather than SF inhibited the growth of bacteria. The toxicity of NPs adsorbed on plain SF was found to be less compared to NPs alone. This study revealed new dimensions regarding the positive impacts of SF at low concentrations. Synthesized NPs applied separately were found to affect the growth of bacteria substantially more than if coated to SF resin beads.