Intensification of Biosynthesizing Tyramine with Engineering Bacteria Expressing L-Tyrosine Decarboxylase By Permeabilization of Cell Membranes

It’s important to develop whole cell biocatalysts with high cell-bound tyrosine decarboxylase (TDC) activity for the biosynthesis of tyramine with higher efficient and lower cost. A recombinant Escherichia coli (Origami(DE3)-pET21a-tdc) strain was constructed by expressing the TDC from Lactobacillus brevis CGMCC 1306 in this study. To increase the membrane permeability and cell-bound TDC activity of Origami(DE3)-pET21a-tdc, we treated the recombinant cells with nine different organic solvents. The results showed permeabilization with organic solvents increased cell-bound TDC activity as a function of their hydrophobicity, and solvents with high hydrophobicity (log P> 2.28) are effective in increasing cell-bound TDC activity of cells. Hexane was the most effective among the tested solvents, which could increase cell-bound TDC activity to 1.48 U•mg^-1 under optimum condition (1% hexane, 10 min). In addition, treatment of the Origami(DE3)-pET21b-tdc under optimum permeabilized condition resulted in structural changes of the cell envelope, but did not substantially affect overall morphology of recombinant cells. By using 0.47 g•L^-1 hexane-treated Origami(DE3)-pET21b-tdc as biocatalyst, 18 g•L^-1 L-tyrosine was almost totally (>99%) converted to tyramine at pH 5.5 and 40 °C within 4.5 h. These results allow systematic selection of suitable organic solvents for improving cell-bound TDC activity of the recombinant E. coli cells and the whole-cell biocatalyst developed here showed great promising for industrial production of tyramine.