Antimicrobial resistomes in plastisphere-associated microbes over aged low-density polyethylene microplastics in the Haora River of Tripura, India.

Microplastics (MPs) provide favorable ecological niches for antimicrobial resistance (AMR) development in aquatic ecosystems. Environmental weathering transforms the inert surfaces of MPs into oxygen-functionalized, reactive interfaces that promote plastisphere formation and selective enrichment of antibiotic-resistant microorganisms. However, studies integrating natural polymer weathering, plastisphere development, and resistome profiling under ecologically relevant conditions remain scarce, particularly in South Asian freshwater ecosystems. To address this knowledge gap, low-density polyethylene (LDPE) pellets were incubated in situ in the anthropogenically impacted Haora River of Northeastern India to investigate how environmental aging-induced surface transformations shape plastisphere formation and association of AMR characteristics. Pristine, aged with biofilm, and aged without biofilm LDPE MPs were comparatively analyzed. Weathering significantly increased surface roughness, crystallinity, and carbonyl index, facilitating dense biofilm formation (OD595 = 1.47 ± 0.02) and elevated intracellular reactive oxygen species (171 net RFU per OD600 unit). Shotgun metagenomic sequencing of plastisphere biofilms was performed on the Illumina NovaSeq 6000 platform. Resistome, mobilome, and metal resistance determinants were annotated using ARG-OAP v3.0, DeepARG Galaxy v1.0.4, MobileOG-db v2.0.1, and BacMet v2.0, respectively. The plastisphere was dominated by the class Gammaproteobacteria, including opportunistic pathogens (Aeromonas, Pseudomonas aeruginosa, and Acinetobacter baumannii), together with clinically relevant antibiotic resistance genes, mobile genetic elements, and metal resistance determinants. These findings demonstrate that naturally aged microplastics act as dynamic reservoirs and vectors for AMR dissemination in riverine environments.