Enhanced biodegradation of bisphenol S by laccase encapsulated in copper-nucleotide metal-organic frameworks

Bisphenol S (BPS) is widely used as a substitute for bisphenol A (BPA) but has also been identified as an endocrine-disrupting compound with considerable biotoxicity. Compared with BPA, BPS exhibits higher chemical stability, and studies on its biodegradation remain limited. In this work, an efficient strategy for BPS biodegradation was developed using a bacterial laccase immobilized in copper-nucleotide metal-organic frameworks (MOFs). The laccase gene from Bacillus licheniformis was heterologously expressed in Escherichia coli, achieving an extracellular activity of 373.8 U/L. The recombinant laccase was purified and subsequently encapsulated in MOFs constructed through the self-assembly of copper ions and nucleotides, including cytidine monophosphate (CMP) and guanosine monophosphate (GMP). After optimization of the immobilization process, the resulting immobilized laccase (Lac@Cu/CGMP) showed enhanced catalytic performance, exhibiting a relative activity of 106.5% compared with the free enzyme. Moreover, Lac@Cu/CGMP displayed improved thermostability, with a longer half-life at 70 °C (3.4 h) than that of the free laccase (2.9 h). Lac@Cu/CGMP achieved 94% degradation of BPS within 1 h and maintained high degradation efficiency after five consecutive reuse cycles. Transformation products were identified by LC-MS, and a plausible degradation pathway was proposed. The biodegradation of BPS involved hydroxylation, deoxygenation, and cleavage of the S-C bond. These results demonstrate that nucleotide-coordinated copper MOFs provide a facile and effective platform for laccase immobilization, highlighting their potential application in the removal of BPS from contaminated environments.