Deciphering the plastisphere nexus in biological wastewater treatment: distinct microbial colonization on biodegradable and conventional microplastics

Abstract

Microplastics (MPs) are ubiquitous in wastewater treatment plants (WWTPs), where their persistent presence has been shown to alter treatment performance and microbial community structure. However, existing studies largely emphasize bulk system responses, while the underlying mechanisms, including biofilm formation on MP surfaces, remain insufficiently characterized. In particular, the extent to which microbial colonization on MP surfaces is selective, polymer-dependent and evolves over time under WWTP conditions remains poorly resolved. To address this gap, this study systematically compares plastisphere development on four conventional polymers, polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET), and a biodegradable polymer, polylactic acid (PLA) under sequencing batch reactor (SBR) conditions. Biofilm biomass increased up to 5-fold, with PLA exhibiting the highest accumulation (OD595nm = 1.067; p < 0.05), substantially exceeding conventional MPs. Intrinsic polymer properties shaped microbial colonization through selective enrichment on MP surfaces. While PLA supported a transient peak in community diversity and selectively enriched plastic-degrading taxa such as Comamonas (~16–25%), continuous hydrolytic oxidation and surface pitting prevented stable long-term community retention. In contrast, conventional MPs converged toward low-diversity biofilms dominated by pioneer genera including Raoultella (~80–90%). Among conventional MPs, PS exhibited the strongest divergence at biofilm maturity, functioning as a persistent reservoir for ESKAPE pathogens. PS specifically enriched Acinetobacter (8.17 log2-fold-change), demonstrating that while biodegradable surfaces promote robust general microbial growth, the structural permanence of conventional microplastics provides a more selective and reliable substrate for long-term pathogen persistence. Together, these findings highlight polymer-specific plastisphere development as a key biological pathway governing MP transformation and microbial partitioning in WWTPs, with implications for MP fate and sludge-associated microbial risks.