| Summary: | Abstract Background The metagenome contains plenty of genetic resources and can be used to search for the novel gene or mutant. Results In this study, the bacterial laccase gene (cueO) with single or multiple mutations was directly cloned based on the metagenome of a chemical plant sludge. An interesting mutation (G276R) was identified from those cloned mutants. The other mutants (G276N, G276Y, and G276K) with improved catalytic efficiency were identified by the saturation mutagenesis on residue G276. The optimal temperature for wild-type CueO enzyme activity was about 70 °C, compared to 60 °C, 50 °C, 50 °C, and 30 °C for the G276R, G276N, G276Y, and G276K mutant enzymes, respectively. The catalytic efficiency (k cat/K m) with 8 mmol Cu2+ of the G276R, G276N, G276Y, and G276K mutants was 1.2-, 2.7-, 1.3-, and 2.7-fold, respectively, compared to the wild-type enzyme. In addition, the mutants G276R, G276N, G276Y, and G276K oxidized the carcinogen benzo[α]pyrene more efficiently compared to the wild-type enzyme. Conclusion All of the results indicate that G276 of CueO plays an important role in enzyme activity, and the useful mutants can be identified based on the metagenome.
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