To evaluate brazzein production in Lactococcus lactis using the nisin-controlled expression (NICE) system. The approach is through analysis of different plasmid/strain combinations.Methods and Results:
Two plasmid/strain combinations of the NICE system were used in brazzein expression: L. lactis NZ9000 harbouring plasmid pNZ8148, and L. lactis IL1403 harbouring plasmid pMSP3545. The former combination proved superior, with a >800-fold increase in His-tagged brazzein expression (to 1·65 mg l−1 of fermentation broth), comparable to expression levels in Escherichia coli. Improved expression resulted in a minor increase in secretion to the medium with the use of the Usp45 signal peptide. The yield of wild-type brazzein corresponded to that of His-tagged brazzein. Wild-type brazzein was partially soluble and low-intensity sweetness was detected.Conclusions:
The plasmid/strain combination of the NICE system has a significant impact on the expression of brazzein where a >800-fold increase was achieved. The greatly increased expression of brazzein resulted in minor improvement in secretion and low-intensity sweetness.Significance and Impact of the Study:
The choice of the plasmid/strain combination of the NICE system was shown to be of extreme importance in brazzein expression.