Microplastic-derived dissolved organic matter components determine Microcystis aeruginosa-bacteria interaction...

Freshwater ecosystems face mounting threats from microplastic pollution, and the dissolved organic matter (DOM) released by these particles represents an emerging ecological risk factor. In this study, a 28-day co-culture experiment was conducted to investigate the comparative effects of photo-aged (UVA-340) MPs-DOM derived from biodegradable poly(butylene adipate-co-terephthalate) (PBAT) versus conventional polyethylene (PE) and polyethylene terephthalate (PET) microplastics on the bacterial community associated with the harmful cyanobacterium Microcystis aeruginosa PCC 7806. Excitation-emission matrix with parallel factor analysis revealed that PBAT-DOM was rich in recalcitrant humic-like components and depleted in labile, protein-like components, whereas PE-DOM and PET-DOM were dominated by protein-like fluorescence. These chemical signatures had strong biological consequences: PBAT-DOM dramatically reduced bacterial diversity and promoted late-stage dominance by Burkholderia-Caballeronia-Paraburkholderia, coupled with a higher inferred contribution of stochastic processes based on null-model and βNTI analyses. In contrast, PE-DOM and PET-DOM maintained higher community evenness and supported temporally variable succession among multiple co-dominant genera (e.g., transient enrichment of Bdellovibrio, Sphingomonas, and Bacteroidota-related genera such as Chryseobacterium/Flavobacterium). Sparse InversE Covariance Estimation for Ecological Association Inference (SPIEC-EASI)-inferred association networks indicated that PBAT-DOM yielded the most modular network with a comparatively lower fraction of positive conditional associations, whereas PE-DOM and PET-DOM maintained well-connected networks with distinct organization patterns. These findings demonstrate that the chemical signature of microplastic-derived DOM critically influences microbial assembly mechanisms. In particular, persistent humic substances from biodegradable plastics may modulate ecological processes by restructuring bacterial communities and carbon cycling, potentially elevating environmental risks in nutrient-sensitive freshwater ecosystems. In summary, microplastic risk assessments should incorporate DOM-mediated effects to better predict long-term impacts on aquatic ecosystems.