A salt-tolerant tetracycline degrading fungal strain of Candida palmioleophila: Characterization and degradation pathway.

Tetracycline (TC), a widely used persistent antibiotic, is frequently detected in aquatic environments and soil, posing serious ecological and health risks. Identifying functional strains capable of TC removal is viewed as a promising solution to controlling TC contamination. In contrast to bacteria, very few fungal strains that degrade TC have been isolated. In this study, a novel salt-tolerant TC-degrading fungus, Candida palmioleophila TDLZ1, was isolated, and its TC degradation capacity, pathways, and genomics were investigated. The strain effectively biodegraded TC under aerobic conditions, utilizing extra carbon sources as co-metabolic substrates, with sodium acetate being the optimum. The strain achieved a maximum TC removal efficiency of 70.7 % under optimal conditions (pH 6-8, 35 °C, 5 % initial dosage of the strain, and 20 g/L salinity). Metabolite analysis identified 14 potential biodegradation intermediates and revealed four new degradation pathways involving demethylation, deamination, ring-opening, and oxidation. TC degradation products became less toxic after treatment with TDLZ1. The strain possessed various oxidoreductases and antibiotic resistance genes including tetA, tetB, tetZ, and tetO, which were essential for TC degradation. Overall, Candida palmioleophila TDLZ1 exhibits substantial potential for efficient antibiotic degradation and environmental remediation, while also offering a vital foundation for expanding the understanding of TC degradation mechanisms in fungi.