Over-expression of Highly Active Triphenylmethane Dyes Decolorization Enzyme(TpmD)Induced by Lactose Instead of IPTG in Escherichia coli BL21(DE3)

The feasibility of expression of TpmD in recombinant E.coli BL21(DE3)induced by lactose instead of IPTG was investigated.The factors affecting the induction of target gene expression such as the optimal time point for induction,the concentration and addition mode of the inducer(lactose)and the induction time were determined.It is established that the optimal induction method is to add 0.4 mmol/L(final concentration)lactose at the mid-log-phase of cell growth,(OD600≈0.8)and incubate at 37°C for 6 h.It would be better to add the lactose in 4 batches(0.1 mmol/L per batch),because lactose can be used as a carbon source by E.coli BL21(DE3).The production of TpmD enzyme induced by lactose was about 35.62% of the bacterial total protein which was no significantly different from that induced by IPTG(≈35.03%),and the expression of TpmD was a little slower than that induced by IPTG.However,the final biomass induced by lactose was higher than that induced by IPTG.These results suggested that the lactose is as effective as IPTG for T7 promoter induction and should be easily scaled up for industrial production of recombinant protein with lower cost.