Nanoplastic Size Governs the Decoupling of Microbial Survival from Antibiotic Degradation

Abstract

Abstract Nanoplastics (NPs) and antibiotics co-occur in wastewater systems, but how NP size influences antibiotic biodegradation by specialized degraders remains unclear. Here, we investigated the effects of europium-doped polystyrene nanoplastics (PS-NPs; PS20 and PS100) on sulfadiazine biodegradation by Arthrobacter sp. strain D2. Modified Gompertz modeling revealed two contrasting inhibition regimes. For PS100, inhibition was dominated by lag-phase prolongation, with no detectable sulfadiazine removal over 48 h at a PS100 concentration of 100 mg L–1. In contrast, PS20 reduced the maximum sulfadiazine degradation rate by ∼40% while causing only minor changes in lag time, indicating rate-dominated inhibition. Quartz crystal microbalance with dissipation monitoring at a model sulfadiazine-enriched interface showed that PS100 markedly reduced the deposition of NP-pre-exposed cells, whereas PS20 only partially impaired adhesion. Transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy further revealed intracellular accumulation of PS20, whereas PS100 remained predominantly extracellular. Phase-specific physiological measurements and transcriptomics suggested that PS20 induced oxidative-stress responses associated with reduced sulfadiazine biodegradation rates, whereas PS100 elicited dose-dependent transcriptional changes during lag-phase extension. Collectively, these findings demonstrate that nanoplastics impair antibiotic attenuation through distinct size-dependent mechanisms involving interface-associated constraints and intracellular interference, highlighting particle size as a key determinant of antibiotic fate in plastic-contaminated wastewater environments.