Cyanobacterial blooms restructure suspended particulate matters and associated microbial community networks to regulate estrogen biodegradation in eutrophic freshwater lakes

Abstract

Suspended particulate matter (SPM), a major carrier of emerging contaminants such as steroid estrogens in freshwater lakes, affects the attenuation of estrogens. However, the extent to which the natural variability and dynamics of SPM and its associated microbial community influence estrogen degradation, particularly during seasonal cyanobacterial harmful algal blooms (CyanoHABs), remains poorly understood. Combining field investigations and laboratory bioassays, we examined how CyanoHABs-driven shifts in SPM physicochemical properties and the associated microbial communities regulate estrone biodegradation in Lake Taihu, a eutrophic freshwater lake in China. Results demonstrated that CyanoHABs significantly increased SPM concentrations (18.6–93.8 mg L⁻¹), organic carbon content, and particle size compared to resuspended SPM in the pre-bloom season, while altering organic matter composition toward autochthonous protein-like substances. Concurrently, the attached microbial community assemblage shifted from deterministic selection to stochastic dominance, forming tightly interconnected microbial co-occurrence networks (average degree: 61.8) with diverse keystone taxa. The enriched labile organics (tyrosine-like substances) and the increased niche-specific degradation pathways associated with negative interspecies interactions enhanced the estrone biodegradation potential (EBP) of SPM from 153.98 to 466.70 ng mg^–1. However, in post-bloom samples, resource homogenization resulted in decreased microbial diversity, niche breadth, and network stability, leading to a 53 % decline in EBP, despite comparable SPM organic carbon content. A PLS-PM model further revealed that organic carbon, protein-like organic matter, and microbial network properties collectively explained 91 % of the variability in SPM-normalized EBP. Notably, pre-bloom samples having the most pronounced deterministic assembly processes demonstrated the highest organic carbon-normalized EBP, with its variability (32 %) explained solely by microbial network complexity. This study underscores the need to integrate SPM dynamics and microbial network stability into management strategies aimed at mitigating estrogen pollution in eutrophic lakes, particularly under escalating CyanoHABs regimes.