Beyond protection: How alginate immobilization enhances microalgal capacity for oxytetracycline removal

Microalgae-based bioremediation is a promising sustainable approach for controlling antibiotic pollution, but conventional suspended cultivation systems remain limited in practical applications. In this study, the application of alginate immobilization as a strategy to enhance Chlamydomonas reinhardtii capacity for oxytetracycline (OTC) removal was investigated. Biomass production of immobilized microalgae was 1.41 times higher (6.14 × 10⁶ cells/mL) than that of the conventional method. Additionally, it enhanced OTC removal efficiency (> 97 %) and OTC stress tolerance. Comprehensive transcriptomic analysis revealed that immobilization-induced extensive molecular adaptations, including reorganization of the photosynthetic apparatus, reprogramming of metabolism toward mixed nutritional modes, and activation of protein quality control systems. Under OTC stress, differentially expressed genes of immobilized cells were 1.36 times more than those of the suspended cells, indicating enhanced antioxidant defense, comprehensive detoxification mechanisms, and coordinated membrane transport systems. The protective alginate matrix shielded cells from direct pollutant contact and facilitated sophisticated cellular adaptations that enhanced both survival and metabolic capacity, providing an efficient and sustainable approach for antibiotic removal from aquatic environments.