Metatranscriptomic and Metabolomic Insights Reveal Enhanced Colonial Microcystis aeruginosa Tolerance to Erythromycin in P-Limited Environment

As the primary component of harmful algal blooms, cyanobacteria exhibit unique adaptation strategies under environmental stress. The impact of erythromycin (ETM), a common macrolide antibiotic in aquatic environments, on colonial cyanobacteria remains unclear. This study examined the chronic toxic effects of different ETM concentrations (0.01, 0.1, 1, 10, 20 and 100 μg/L) on colonial Microcystis aeruginosa (M. aeruginosa) under varying nutrient conditions. Results showed that at 0.01–1 μg/L, ETM could promote the growth of M. aeruginosa, while high concentrations of ETM (≥10 μg/L) significantly inhibited growth (p < 0.05). Low-level ETM exposure accelerates M. aeruginosa growth by boosting PSII efficiency, extracellular polymeric substance (EPS) production, and the activities of superoxide dismutase (SOD) and catalase (CAT). Metatranscriptomic and metabolomic analyses further reveal that this stimulation is underpinned by enhanced trace-element uptake, reinforced carbon cycling, and increased biosynthesis of proteins, polysaccharides, and chlorophyll precursors. High-level ETM exposure inhibited the growth of M. aeruginosa, as evidenced by decreased photosynthesis, damaged membranes and suppressed metabolic activity. Metatranscriptomic and metabolomic analyses showed the upregulation of photosynthesis andpathways, metabolic pathways, and the accumulation of potent allelochemicals in P-limited cells exposed to 10 µg/L ETM relative to 10 µg/L ETM in nutrient-replete BG11 medium. Furthermore, phosphorus deficiency may enhance the potential of net methane formation. These findings underscore the complex interactions between antibiotic exposure and nutrient stress in cyanobacteria, with significant implications for environmental management of antibiotic contamination.