Fig. 1

Construction of the glucose oxidase expressing strains of A. niger. A Schematic diagram of the gox expression cassette containing the promoter of the fopA gene (PfopA), the gox gene, the trpC terminator (TtrpC) and the selection marker ptrA. The expression cassette was constructed as described in “Materials and methods” section. B Assay of glucose oxidase on the GOD-POD bienzymatic detection plate. The same concentrations of spores of the glucose oxidase-expressing transformants GOD-1, GOD-3 and GOD-39 were spotted on the CD plate. Then the amount of glucose released was detected by the GOD-POD bienzymatic system. Glucose oxidase activity was tested by a dark brown halo surrounding the colonies. A. niger ATCC 20611 was used as the control. C Relative expression levels of gox in the glucose oxidase 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 glucose oxidase activities in different cell fractions of transformants. 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. 20611, A. niger ATCC20611