PE microplastics and sulfadiazine drive cross-domain microbial restructuring and antibiotic resistance gene dynamics in biofilms

Microplastic-associated biofilms are increasingly recognized as hotspots for microbial colonization and the accumulation of antibiotic resistance genes (ARGs) in environmental systems. However, most studies have focused primarily on bacterial communities, while how fungal and archaeal communities respond to combined microplastic and antibiotic exposure, and how these responses influence ARG dynamics, remain poorly understood. In this study, biofilms were exposed to polyethylene (PE) microplastics (MPs) of varying sizes and concentrations, with or without the sulfonamide sulfadiazine (SD). Bacterial, fungal, and archaeal communities were jointly characterized, along with sulfonamide resistance genes (SRGs; sul1-sul4) and the class 1 integron integrase gene (intI1). Both PE MPs and SD significantly altered microbial community composition, with domain-specific responses observed based on α- and β-diversity analyses. Distinct shifts were observed across bacterial, fungal, and archaeal communities. Partial redundancy analysis identified SD exposure and microbial community structure as major contributors to ARG variation. Co-occurrence network analysis further revealed domain-specific associations between microbial taxa and ARGs, with sul1-sul3 mainly linked to bacterial taxa, while sul4 showed associations with fungal communities, likely reflecting co-occurrence patterns rather than direct gene carriage. Overall, these results demonstrate that PE MPs reshape multi-domain microbial restructuring and indirectly influence ARG distribution through changes in community structure. Our findings underscore the importance of considering bacteria, fungi, and archaea when evaluating antibiotic resistance risks in microplastic-contaminated environments.