Fig. 3

Construction of the peroxidase-FopA expressing strains of A. niger. A Schematic diagram of the pod-fopA expression cassette containing the promoter of the fopA gene (PfopA), the horseradish roots pod gene, the fopA sequence and the trpC terminator (TtrpC). The expression cassette was constructed as described in “Materials and methods” section. B Assay of peroxidase and FopA on the GOD-POD bienzymatic detection plate. The same concentrations of spores of the peroxidase-expressing transformants DPOF-1, DPOF-3 and DPOF-14 were spotted on the CD plate. Then the amount of glucose released was detected by the GOD-POD bienzymatic system. Peroxidase activity was tested by a dark brown halo surrounding the colonies. A.niger ATCC 20611 and A. niger ∆fopA were used as the control. C Relative expression of pod in the peroxidase-FopA expressing transformants. Actin was used as a reference gene and the 2-^ΔΔCt method was used for calculating relative expression levels. D Determination of the peroxidase activities in different cell fractions of transformants using glucose as the substrate. E Determination of fructofructofuranosidase activities of the peroxidase-FopA transformants in different cell fractions by ABTS method. Error bars represent the standard deviation of three independent experiments. “a/b/c” above the bars indicate significant differences at P < 0.01. n.d., not detected