Fig. 9

Sugar release from ball-milled wheat straw by killed cells. Washed, azide-treated cells were incubated in a suspension with 1 % (w/v) ball-milled wheat straw. Samples were taken at 4, 20, 44, 68, and 92 h and the concentrations of reducing sugars were analysed by DNS assay. Black triangles, CEL21, overexpressing the native srtA gene and producing a cellulosome consisting of Xyn10A-FLAG, Cel9G-FLAG, Cel48F-FLAG and the anchored scaffoldin CipC2F3-CA_C0205ss; black squares, CEL19, overexpressing the native srtA gene and producing a cellulosome with all three enzymes and the unanchored scaffoldin CipC2F3; open circles, wheat straw only. Results represent the average of three technical replicates with error bars representing standard error of the mean. Positive control was carried out using 100 μl commercial cellulase from T. reesei (Sigma-Aldrich) and gave a final reducing sugar concentration of 1.71 mg/ml reducing sugar at 92 h (omitted for clarity). Difference between the two C. acetobutylicum strains is significant to P ≤ 0.01 at 44 h (**), P ≤ 0.001 at 68 h (***), and P ≤ 0.0001 at 92 h (***). Results were analysed using GraphPad Prism software. The data obtained from the sugar release assay have been provided in Additional file 3