Elucidating the enzyme-driven degradation of macrolide antibiotics in a bacterial-algal symbiotic system.

With the widespread use of macrolide antibiotics, their presence in aquatic environments has emerged as a significant ecological concern. Clarithromycin (CLA), a representative macrolide antibiotic, was used to investigate the stress response and metabolic degradation dynamics within a bacterial-algal symbiotic system operated in a novel photobioreactor. Ten days before the addition of CLA, the bacterial-algal system was in the period of symbiotic acclimatization and secreted considerable EPS with polysaccharide content as high as 77.84 ± 2.05 mg/g SS, which provided a high density of adsorption sites for CLA. Up to 96.74% of CLA was degraded, 0.89% was adsorbed and 0.23% was accumulated. In this study, three degradation pathways of clarithromycin were hypothesized, with N-desmethyl-Clari, 2-Phospho-Clari and de-desotamine-Clari being the major degradation products. Expression of the specific degradation enzymes phosphotransferase and erythromycin esterase increased by 7.43-fold and 23.55-fold, respectively, compared to the control. Sphingopyxis was the dominant flora. The transcriptomics results showed that the bacterial-algal system resisted stress and degraded CLA through regulatory mechanisms that enhanced energy metabolism, substance exchange, signaling responses and attenuated competitive behavioral processes. In this study, a green and efficient CLA removal method was developed and theoretical support was provided for the treatment of CLA-containing wastewater. This study not only provides a viable and eco-friendly solution for the immediate remediation of clarithromycin-contaminated water but also offers a sustainable microbial-enhanced framework with promising potential for long-term application in the treatment of wastewater containing emerging refractory antibiotics.