Cellulose/polyester-blended microplastics amplify plastisphere pathogen and antibiotic resistome risks.

Microplastics (MPs) are important vectors for antibiotic resistance genes (ARGs) in anaerobic digestion systems, yet the risks posed by cellulose/polyester-blended materials remain poorly understood. In this study, commercial airlaid paper (AP; 45 % cellulose and 55 % polyester), polyethylene (PE), polypropylene (PP), and polystyrene (PS) were incubated in anaerobic reactors for 60  days. Biofilm characterization, extracellular polymeric substances (EPS) analysis, 16 S rRNA sequencing, and metagenomics were used to compare plastisphere formation, microbial assembly, ARG/mobile genetic element (MGE) profiles, and potential pathogen composition. Owing to its fibrous structure and bioavailable cellulose fraction, AP exhibited the highest biofilm biomass and EPS content. In contrast, PE, PP, and PS induced stronger interfacial stress, especially PS, as indicated by increased reactive oxygen species, lactate dehydrogenase release, and enrichment of oxidative stress, SOS response, and multidrug efflux pump related genes. Metagenomic analysis showed that fully synthetic MPs mainly enriched multidrug resistance genes, whereas AP selectively enriched polymyxin resistance genes, particularly Mcr-5.1 and Mcr-5.2. AP also exhibited the highest ARG-MGE co-localization rate (12.7 %) and antibiotic resistance risk. Overall, these findings identify polymer composition as a key factor shaping plastisphere resistome assembly and indicate that cellulose/polyester-blended materials require specific consideration in sludge-associated antimicrobial resistance risk assessments.