Fig. 5

Activity analysis of cellulases and cellulase fractions measured by quantitative 4-MUC assay. a Analysis of supernatants of cell lysates from four subclones (S1C, S3C, S5C, S8C and F1C), in units of fluorescent signal intensity. The supernatants from each of the four subclones were incubated at 37 °C (light grey), 60 °C (medium dark grey) or 80 °C (dark grey), as indicated in figure, for 6 h to test the thermal stability of each respective cellulase. Values for a subclone with different superscripts (a, b, ab) were significantly different (P < 0.05) by one way ANOVA followed by Turkey multiple comparison. b Activity assay using crude cell extracts, heated at 65 °C for 20 min, with activity/mg protein plotted for extracts originating from E. coli expressing the four cellulase S1C, S3C, S5C, and F1C, in comparison to the E. coli negative control. c Activity assay of the Ni–NTA isolated protein, with activity/mg protein plotted for untreated (medium grey) as well as heat treated (dark grey; 65 °C, 20 min) samples. d Cellulase activity measured in crude cell extract from cells producing native enzyme F1 (F1C), codon optimized enzymes F1 (F1C optim.), as well as from cells not producing enzyme F1 (E. coli background). All samples were analysed with and without heat treatment (65 °C, 20 min). Error bars represent standard deviations from three independent measurements