Enhanced production of dimethyl phthalate-degrading strain Bacillus   sp. QD14 by optimizing fermentation medium

Background: Integrated statistical experimental designs were applied to optimize the medium constituents for the production of a dimethyl phthalate (DMP)-degrading strain Bacillus sp. QD₁₄ in shake-flask cultures. A Plackett–Burman design (PBD) was applied to screen for significant factors, followed by the Steepest Ascent Method (SAM) to find the nearest region of maximum response. A Box–Behnken design (BBD) of the Response Surface Methodology (RSM) was conducted to optimize the final levels of the medium components.
Results: After the regression equation and response surface contour plots were analyzed, the concentrations of glucose, corn meal and NaCl were found to significantly influence the biomass of DMP-degrading bacteria. A combination of 22.88 g/L of glucose, 11.74 g/L of corn meal, and 10.34 g/L of NaCl was optimum for maximum biomass production of Bacillus sp. QD₁₄. A 57.11% enhancement of the biomass production was gained after optimization in shake-flask cultivation. The biomass production of Bacillus sp. QD₁₄ reached 9.13 ± 0.29 × 10⁸ CFU/mL, which was an excellent match for the predicted value, and the mean value of the match degree was as high as 99.30%.
Conclusion: In this work, the key factors affected by the fermentation of DMP-degrading strain Bacillus sp. QD₁₄ were optimized by PBD, SAM and BBD (RSM); the yield was increased by 57,11% in the conditions in our study. We propose that the conditions optimized in the study can be applied to the fermentation for commercialization production.

Keywords
Bacillus; Box–Behnken design; Dimethyl phthalate; Medium optimization; Plackett–Burman design