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.