3.3 Screening of the mutant library of MPH variants
As shown in Figure 3a, the mutants were grown on LB plate containing 50 mg/L chlorpyrifos. A transparent halo could form around the colony when chlorpyrifos is hydrolyzed by MPH (Xie et al. 2014). Enlarged halo indicated enhanced MPH activity, which may be caused by improved catalytic efficiency or increased MPH number. Two mutants, named MT1 and MT2, which formed significantly bigger transparent halos were screened from about 12000 colonies. When grown in liquid medium, the growth curves of both mutants were similar with that of strain BPC1. (data not shown), but the maximum extracellular MPH activity of mutants MT1 and MT2 were 2.47 and 2.77 fold that of strain BPC1 (Figure 3b), respectively.