Biofilm-Mediated Bacterial Sorption onto Microplastics in Water: Mechanistic Pathways, Plastisphere Formation, and Implications for Disinfection Performance

Abstract

Microplastic-associated biofilms represent emerging interfaces for microbial attachment, persistence, and transport in aquatic environments, yet the mechanisms governing bacterial sorption onto microplastics and their implications for water treatment remain insufficiently resolved. This study investigated bacterial colonization, sorption behavior, plastisphere assembly, and disinfection interference associated with microplastics in water using high-throughput 16S rRNA sequencing, scanning electron microscopy, Fourier-transform infrared spectroscopy, Brunauer–Emmett–Teller surface analysis, confocal laser scanning microscopy, flow cytometry, and chlorine disinfection assays. Microplastics recovered from raw surface water showed pronounced surface modification and altered functional groups. Biofilm formation and extracellular polymeric substances were clearly observed on microplastic surfaces after exposure to water. The maximum thickness of the bottom biofilm layer in contact with the microplastics reached 43.4 μm, whereas the upper biofilm layer reached 19.53 μm. Sequencing analysis indicated that microplastics altered bacterial community structure and supported distinct plastisphere assemblages compared with the surrounding water phase. Adsorption and desorption assays demonstrated that bacteria could attach and detach from microplastics. The maximum numbers of Escherichia-Shigella attached to and detached from microplastics were approximately 4 × 10⁵ CFU/mL and 2 × 10⁶ CFU/mL, respectively. Notably, the presence of microplastics reduced the effectiveness of chlorine disinfection against Escherichia-Shigella, suggesting that microplastic-associated bacteria may be partially protected from oxidative inactivation. These findings demonstrate that microplastics are not merely passive particles in water but dynamic microbial carriers that can influence bacterial persistence, community assembly, and treatment efficiency. The results highlight the need to incorporate microplastic-biofilm interactions into water-quality assessment and disinfection-risk frameworks.