Fig. 2

Construction of the glucose oxidase-FopAC expressing strains of A. niger. A Schematic diagram of the gox-fopAC expression cassette containing the promoter of the fopA gene (PfopA), the gox gene, the encoding sequence for the C-terminal domain of the fopA (fopAC), 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 activity on the GOD-POD bienzymatic detection plate. The same concentrations of spores of the glucose oxidase-expressing transformants GOF-1, GOF-2 and GOF-3 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-FopAC expressing transformants. Actin was used as a reference gene and the 2-^ΔΔCt method was used for calculating relative expression levels. D Determination of fructofructofuranosidase activities of the glucose oxidase-FopAC transformants in different cell fractions. E 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