Fig. 8

Release of reducing sugar from beechwood xylan, CMC, PASC and wheat straw by 10-fold concentrated supernatants from recombinant strains of C. acetobutylicum. Supernatants were collected from recombinant strains of C. acetobutylicum and concentrated 10-fold; concentrated supernatants were incubated with 1 % substrate and the released sugars analysed by DNS assay. The following strains were analysed: CEL07, overexpressing the native srtA gene; CEL16, producing Xyn10A, Cel9G and Cel48F and overexpressing the native srtA gene; CEL19, producing the three hydrolases and the unanchored CipC2F3 scaffoldin and overexpressing the native srtA gene; and CEL21, producing the three hydrolases and the wall-anchored scaffoldin CipC2F3-CA_C0205ss and overexpressing the native srtA gene. Differences between levels of released sugars were measured by 1-way ANOVA. Results represent the average of three technical replicates, with the DNS assay also carried out in triplicate; error bars represent standard error of the mean. Hydrolysis reactions were carried out for 2 h for xylan and CMC and 72 h for PASC and wheat straw. Significantly more reducing sugar was released from xylan by strains CEL16 and CEL19 (P ≤ 0.0001, ****) and by CEL21 (P ≤ 0.001, ***) when compared to CEL07. For CMC, there were no statistical differences between any of the strains. For PASC, there was a significant difference in released reducing sugar between CEL07 and the strains CEL15 and CEL19 (P ≤ 0.001, ***) and between CEL07 and CEL21 (P ≤ 0.01, **); there was also a significant difference (P ≤ 0.05) between CEL21 and strains CEL16 and CEL19. For wheat straw, there was a significant difference (P ≤ 0.05, *) between CEL07 and CEL16, between CEL07 and CEL19 (P ≤ 0.0001, ****) and between CEL07 and CEL21 (P ≤ 0.001, ***); there were also significant differences between CEL16 and CEL19 (P ≤ 0.001), CEL16 and CEL21 (P ≤ 0.05), and CEL19 and CEL21 (P ≤ 0.05). The data obtained from the sugar release assay have been provided in Additional file 3