Heterologous production of a temperature and pH-stable laccase from Bacillus vallismortis fmb-103 in Escherichia coli and its application

[Display omitted] •The recombinant laccase (fmb-rL103) production reached to 3420U/L through the auto-induction strategy.•An effective and low-cost purification method was established to purify fmb-rL103.•Fmb-rL103 was temperature and pH-stable.•Fmb-rL103 can efficiently degrade malachite green (MG) in combination with mediators. To enhance laccase yield, the laccase gene from Bacillus vallismortis fmb-103 was cloned and heterologously expressed in Escherichia coli BL21 (DE3) cells. The auto-induction strategy was applied during fermentation, and the process was controlled, as follows: Cu2+ was added when the optical density at 600nm (OD600) was 0.3, the fermentation temperature was adjusted to 16°C when the OD600 was 0.9, and fermentation was stopped after 50h. The yield of recombinant laccase was up to 3420U/L, as assayed by 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid). Recombinant laccase was purified 4.47-fold by heating for 10min at 70°C and dialyzing against 50–60% ammonium sulfate, retained more than 50% activity after 10h at 70°C, and demonstrated broad pH stability. Malachite green was efficiently degraded by recombinant laccase, especially in combination with mediators. These results provided a basis for the future application of recombinant laccase to malachite green degradation.