Community-Driven Sensitivity of <i>Microcystis aeruginosa</i> to Acetylacetone: How Associated Bacteria Influence Cyanocidal Efficacy

Harmful cyanobacterial blooms threaten freshwater ecosystems globally. While the dominant Microcystis aeruginosa is sensitive to cyanocides such as acetylacetone (AA), the efficacy is strongly modulated by the associated bacteria. Here, we observed a 56.7% reduction in cyanobacterial inhibition efficacy of AA to one Microcystis aeruginosa strain after 6 months of prolonged culturing. The altered response was driven by three bacterial-mediated mechanisms: (1) Community restructuring: The temporal evolution reduced species richness but increased evenness; (2) Functional taxa enrichment: Pseudomonas (biofilm formation), Porphyrobacter (phototrophic energy supply), and Limnobacter (organic matter degradation) became dominant in AA-tolerant strains; (3) Metabolic adaptation: Quorum sensing (two-component systems) and lipid metabolism pathways were upregulated. Our findings show that the associated bacteria act as dynamic mediators of cyanocidal resilience, advocating for bacterial-targeted strategies in bloom control.