Iron-microbe synergy in laccase deactivation and PAH bioremediation：Insights from four contrasting soils

The rapid deactivation of enzymes in soils—a major barrier to practical enzymatic remediation—remains mechanistically unresolved under realistic mineral-organic-microbial conditions. Here, we uncover the governing principles behind this bottleneck by investigating laccase inactivation during polycyclic aromatic hydrocarbon (PAH) biodegradation in four distinct soils (clay, red, black, loess). A critical paradox was observed: red soil achieved the highest benzo[ a ]pyrene removal rate (52.72% within 24 h) yet suffered the most rapid laccase activity loss (83% within 24 h). Multi-technique analysis (XPS, EPR, FTIR) linked this to a distinct conformational signature in red soil laccase—maximal α-helix content (21.4%), intensified T1 Cu signal (gII=2.3), and elevated -C O/-C-N bonds. A partial least squares structural equation model (PLS-SEM) revealed the core mechanism: iron-mediated enhancement of microbial fermentation activated T1 Cu sites, which subsequently governed overall laccase activity (path coefficient = 0.64, p  < 0.05). We propose a unified mechanism whereby soil iron drives a conformational shift in the T1 copper center (increased α-helix), optimizing it for initial substrate oxidation but simultaneously rendering it prone to catalytic deactivation. This establish a “mineral–microbe–enzyme” coupling framework, revealing that native soil iron catalytically tunes and subsequently inactivates the enzyme. This mechanistic understanding is critical for transitioning from empirical applications to the rational design of stabilized enzymatic remediation strategies.