An alkali-halophilic laccase facilitates highly efficient conversion of lignin into polyhydroxybutyrate

Lignin valorization is crucial for sustainable biorefineries, yet its complex structure challenges efficient conversion. Here, we report an alkali-halophilic laccase (Lacc) from Halomonas sp. Y3 that enables highly efficient lignin-to-polyhydroxybutyrate (PHB) conversion. Lacc exhibits exceptional properties: optimal activity at pH 9.0 and 200 mM NaCl, >75 % activity retention at 70 °C, and 230 % activity enhancement under high salinity. It cleaves β-O-4, β-5, and β-β lignin linkages, achieving 47.52 % degradation when coupled with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS, laccase-mediator system, LMS), outperforming fungal/bacterial laccases in alkaline conditions. Integrated depolymerization-fermentation processes were developed. Separate depolymerization and fermentation (SDF) with LMS pretreatment yielded 1.85 g/L PHB (18.52 % conversion). An optimized open nonisothermal simultaneous process (ONSDF) balanced Lacc (40 °C) and Halomonas sp. Y3 fermentation (30 °C), achieving record PHB production (1.97 g/L, 19.65 % conversion) from lignin-surpassing most microbial systems. Multi-omics analyses reveal the degrading mechanism: demethoxylation and side-chain modification generate aromatic monomers (e.g., 4-hydroxybenzoic acid), funneled into PHB via gentisate/benzoate pathways. This alkali-halophilic synergy enables non-sterile operation, reducing costs. This work provides: 1) a novel alkali-halophilic laccase for harsh industrial conditions; 2) a one-pot ONSDF strategy for scalable lignin valorization; and 3) insights into lignin depolymerization pathways. The findings advance lignin bioconversion and sustainable bioplastic production.