Development of a recombinant Bacillus ligniniphilus L1 laccase-rice straw biochar composite for efficient...

This study reports the development of a recombinant Bacillus ligniniphilus L1 laccase-rice straw biochar composite and its application in deltamethrin bioremediation. The L1-laccase was heterologously expressed in E. coli BL21 (DE3), purified to a specific activity of 186 U/mg, and covalently immobilized on NaOH- and glutaraldehyde-modified rice straw biochar. Molecular docking against the AlphaFold2-predicted structure (UniProt E9PZ36) yielded a binding affinity of - 6.9 kcal/mol, with one hydrogen bond to MET216 (2.77 Å) and hydrophobic contacts with MET197, MET202, and MET210. However, 100 ns molecular dynamics simulations confirmed a conformationally stable complex (RMSD ~0.42 nm, radius of gyration ~2.21 nm, SASA ~215 nm²). Immobilization shifted the activity optima from pH 7.5 and 45 °C (free) to pH 8.0 and 50 °C (immobilized) and markedly improved stability: the immobilized enzyme retained 74% of its initial activity after 6 days at 4 °C and 18% after 8 catalytic cycles. The apparent Kₘ increased from 0.38 mM (free) to 0.54 mM (immobilized), with kcat values of 178 s⁻¹ and 130.7 s⁻¹, respectively. Under an aggressive deltamethrin load (1000 mg/L), the immobilized laccase achieved 92.3% degradation within 18 h at 50 °C, compared with 68.7% for the free enzyme, producing two major phenolic metabolites (tR = 1.854 and 2.436 min) and one minor unidentified product. These results establish a cost-effective, reusable, and scalable biocatalyst for the bioremediation of pyrethroid-contaminated environments.