Improving an Escherichia coli-based biocatalyst for terpenol glycosylation by variation of the expression system.

Glycosides are becoming increasingly more relevant for various industries as low-cost whole-cell-biocatalysts are now available for the manufacture of glycosides. However, there is still a need to optimize the biocatalysts. The aim of this work was to increase the titre of terpenyl glucosides in biotransformation assays with E. coli expressing VvGT14ao, a glycosyltransferase gene from grape (Vitis vinifera). Seven expression plasmids differing in the resistance gene, origin of replication, promoter sequence, and fusion protein tag were generated and transformed into four different E. coli expression strains, resulting in 18 strains that were tested for glycosylation efficiency with terpenols and a phenol. E. coli BL21(DE3)/pET-SUMO_VvGT14ao yielded the highest titres. The product concentration was improved 8.6-fold compared with E. coli BL21(DE3)pLysS/pET29a_VvGT14ao. The selection of a small solubility-enhancing protein tag and exploitation of the T7 polymerase-induction system allowed the formation of increased levels of functional recombinant protein, thereby improving the performance of the whole-cell biocatalyst.