Improved catalytic activities of a dye-decolorizing peroxidase (DyP) by overexpression of ALA and heme biosynthesis genes in Escherichia coli

Hemoproteins are biotechnologically important heme-containing enzymes, and their production often requires optimal supply of precursors, such as 5-aminolevulinic acid (ALA) and hemin. In this work, endogenous ALA biosynthesis in Escherichia coli was increased as a strategy to improve catalytic activities of a recombinant dye-decolorizing peroxidase (DyP) from Bacillus subtilis. The positive effects of this expression system (pHemAL-DyP) are compared with individually expressed DyP strains grown with (pDyP + Hemin) and without (pDyP) the addition of hemin. The pHemAL-DyP plasmid increased intracellular ALA up to 117.5 mg/L, a 4.0-fold increased from control strain (pET22b, 29.7 mg/L of ALA). Soret peak in the UV-vis spectra was the highest for pHemAL-DyP strain with Reinheitszahl (A₄₀₈/A₂₈₀) value of 0.65 indicating higher heme content in the DyP produced compared to pDyP (0.39) and pDyP + Hemin (0.46). Peroxidase activity was increased up to 66.7 U/mg in the pHemAL-DyP strain compared to 39.0 and 43.4 U/mg for pDyP and pDyP + Hemin, respectively. Decolorization percentage of Reactive Blue 19 dye was the highest in the pHemAL-DyP strain with 84.7% as compared to the pDyP (69.9%) and pDyP + Hemin (72.8%) systems. In brief, enzymatic properties of recombinant DyP were successfully enhanced using this genetic engineering strategy thus eliminating the need for costly exogenous precursors.