Tolerance evolution in cyanobacteria under chronic copper and moxifloxacin stress: Phenotypic plasticity and genomic fixation

Whether antibiotic resistance driven by environmental pollutant represents a transient ecological response or a permanent evolutionary shift remains a critical knowledge gap in global health. Here, we tracked the antibiotic tolerance evolution of the primary producer Synechocystis sp. PCC 6803 under chronic exposure (140 d) to environmentally relevant concentrations of copper [Cu(II): 250 μg/L] and the fluoroquinolone antibiotic moxifloxacin [MOX: 20 μg/L], respectively. The evolved cyanobacterial populations acquired high-level tolerance without obvious fitness costs. Notably, this tolerance exhibited dual characteristics: multidrug cross-tolerance was transient and fully reversible upon stressor removal, whereas tolerance to the selective agent itself [Cu(II) or MOX] was stable and heritable. Multi-omics analyses revealed the mechanistic basis for this divergence. Transient tolerance was driven by a highly dynamic form of phenotypic plasticity—manifested as transcriptional reprogramming and large-scale genomic variations that conferred a temporary fitness advantage but were rapidly lost without selective pressures. In contrast, the persistent resistance was cemented by the point mutation in rpoB gene. Our findings demonstrate that pollutants in the environment may drive the antibiotic resistance evolution in cyanobacteria and foster persistent stress tolerance. This highlights the potential risks of primary producers in the aquatic environment as an antibiotic resistance reservoir and vectors for antibiotic resistance dissemination, underscoring the necessity of integrated risk assessment and source control strategies under the “One Health” framework.