Abstract:

Objective: To provide reference for large-scale production of thermostable cellullase by engineered bacteria fermentation. Methods: The optimal fermentation medium of recombinant Escherichia coli obtained from Clostridium thermocellum for the production of thermostable cellullase were investigated using quadratic regression orthogonal composite design coupled with integrated correlation coefficient analysis, where four factors and their relative importance were analyzed. Results: The quadratic regression equation between four experimental factors and cellulose activity was presented as follows: Y2 = 45.858－1.653Z1－1.258Z2Z3－2.012Z12－1.499Z22－1.415Z32－1.719Z42. Variance analysis exhibited a significant difference. The optimal fermentation medium of the recombinant strain for the production of thermostable cellullase consisted of 15.9 g/L lactose, 10 g/L wheat bran, 15 g/L ammonium sulfate, 5 g/L corn syrup and 1.0 g/L calcium carbonate. The theoretical cellullase activity was 46.19 U/mL after 4 h of induction time. However, the actual cellullase activity was 70.78 U/mL. Integrated correlation coefficient analysis showed the importance of four factors according to the following order of inducer X1 (lactose)＞nitrogen source X3 (ammonium sulfate and corn syrup)＞calcium concentration X4 (calcium carbonate)＞carbon source X2 (wheat bran). The indirect effects from cross-interaction on cellulase activity were all larger than the direct effects. Conclusion: The combinatorial application of integrated correlation coefficient and quadratic regression orthogonal composite design exhibits a complementary effect, which benefits the optimization of fermentation medium of recombinant Escherichia coli obtained from Clostridium thermocellum for the production of thermostable cellullase.

Key words: Clostridium thermocellum cellullase, quadratic regression orthogonal composite design, integrated correlation coefficient, optimization