Sustainable Biodegradation of Triclosan and Sulfamethoxazole with Cyanobacteria: Resistance Mechanism and Metabolic Transformation

Pharmaceuticals and personal care products (PPCPs) are emerging pollutants in aquatic environments, posing significant ecological risks. Cyanobacteria, as primary producers in aquatic ecosystems, are crucial for ecosystem health. Understanding the toxicological effects and metabolic mechanisms of PPCPs in cyanobacteria is essential for evaluating environmental risks and bioremediation feasibility. This study reveals that while both sulfamethoxazole (SMX) and triclosan (TCS) inhibit algal growth by reducing photosynthetic pigment synthesis and activity, Synechocystis sp. PCC 6803 shows markedly different sensitivities to these compounds. The 72-h EC50 values for TCS and SMX were 14.55 μg/L and 19.74 mg/L, respectively. Despite these differences, Synechocystis sp. PCC 6803 achieved removal rates of 89.58% for TCS and 87.60% for SMX. Biodegradation was the primary mechanism for both, but TCS removal also involved biological adsorption and bioaccumulation, mechanisms absent for the hydrophilic SMX. Metabolic pathway analysis identified glycosyltransferase-mediated reactions as key in TCS metabolism, while N4-hydroxylation-SMX (m/z 270) was a critical intermediate in SMX degradation. Notably, the sll1732 gene was found to play a pivotal role in SMX degradation. This research offers insights into the interactions between Synechocystis sp. PCC 6803 and these PPCPs, highlighting its potential for environmentally sustainable bioremediation.