Characterization of acetaminophen biodegradation performance and genomic features of Labrys sp. XQ-1

Acetaminophen (N-acetyl-p-aminophenol, APAP) is a widely used pharmaceutical and an emerging micropollutant of ecological concern in aquatic environments. However, the taxonomic diversity of APAP-degrading bacteria remains poorly understood. An APAP-degrading strain, Labrys sp. XQ-1, was obtained from municipal wastewater and was capable of utilizing APAP as the sole added carbon and energy source for growth. Removal of 99% of 100 mg/L APAP was achieved within 36 h under optimal conditions (30 °C, pH 7.0, 1% NaCl). Kinetic analysis indicated that APAP degradation by strain XQ-1 was best described by a first-order model (R² = 0.988). Genome sequencing further identified a hydrolase-encoding gene, apbH, classified within the Amidase Signature (AS) superfamily. Functional assays confirmed that ApbH could catalyze the initial deacetylation of APAP to 4-aminophenol. Enzyme kinetics, molecular docking analysis, and site-directed mutagenesis supported the functional importance of Lys135, Ser210, and Ser234 in ApbH-mediated APAP transformation. Batch reactor experiments further confirmed efficient APAP removal in both mineral salt medium and simulated wastewater, with transient accumulation and subsequent disappearance of 4-AP. These findings expand the known diversity of APAP-degrading bacteria and provide new insights into its biodegradation.