Chiang Mai Journal of Science

 The production of high level b-xylosidase with b-xylanase by mixed culture was investigated by using low cost rice straw as a substrate. Among 180 Gram’s positive spore forming bacteria, Bacillus amyloliquefaciens DMKUB24 was selected for its highest production of b-xylosidase, 7.9 U/mL, with 2.3 U/mL of b-xylanase activity, whereas B. pumilus DMKUB39 was selected for its highest production of b-xylanase, 10.7 U/mL, with 0.6 U/mL of b-xylosidase activity. However, b-xylosidase and b-xylanase produced by the mixed cultures of strains DMKUB24 and DMKUB39 were 9.8 U/mL and 11.3 U/mL, respectively, which were higher than that of produced by monoculture of each strain. To enhance the production of high level of b-xylosidase with b-xylanase, the mixed culture strains were therefore employed, using the Plackett-Burman (PB) experimental design to screen important parameters influencing the co production of b-xylosidase and b-xylanase. NaOH-treated rice straw, peptone, MgSO4×7H2O and initial pH medium were the main factors influencing the production of mixed enzymes. Central composite design (CCD) and response surface methodology (RSM) were applied to determine the optimal concentration of each significant variable. The maximal b-xylosidase activity of 46.1 U/mL with 24.0 U/mL of b-xylanase activity in a 1L stirrer fermentor at 48 h cultivation was obtained from the optimized medium of b-xylosidase production, while the maximal b-xylanase activity of 49.3 U/mL with  36.0 U/mL of b-xylosidase activities was also achieved from the optimized medium of  b-xylanase production.