Thermo and halo tolerant laccase from Bacillus sp. SS4: Evaluation for its industrial usefulness

Laccases are unable to oxidize the non-phenolic components of complex lignin polymer due to their less redox potential (E0). Catalytic efficiency of laccases relies on the mediators that potentiates their oxidative strength; for breaking the recalcitrant lignin. Laccase from Bacillus sp. SS4 was evaluated for its compatibility with natural and synthetic mediators. (2 mM). It was found that acetosyringone, vanillin, orcinol and veratraldehyde have no adverse effect on the laccase activity up to 3 h. Syringaldehyde, p-coumaric acid, ferulic acid and hydroquinone reduced the enzyme activity ≥50% after 1.0 h, but laccase activity remained 100 to ~120% in the presence of synthetic mediators HBT (1-Hydroxylbenzotrizole) and ABTS. (2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) after 3 h. MgSO₄ and MnSO₄ (40 mM) increased the enzyme activity 3.5 fold and the enzyme possessed ≥70% activity at a very high concentration. (2 M) of NaCl. The enzyme retained 40-110% activity in the presence of 10% DMSO (dimethylsulfoxide), acetone, methanol and ethyl acetate. On the other hand, CuSO₄ (100 μM) induced the laccase production 8.5 fold without increasing the growth of bacterial cells. Laccase from SS4 appropriately decolorized the indigo carmine (50 μM) completely in the presence of acetosyringone (100 μM) within 10 min and 25% decolorization was observed after 4 h without any mediator.