Optimization of fermentation conditions for the production of recombinant feruloyl esterase BpFae^T132C-D143C

Feruloyl esterases (FAEs) are a crucial component of the hemicellulose-degrading enzyme family that facilitates the degradation of lignocellulose while releasing hydroxycinnamic acids such as ferulic acid with high added value. Currently, the low enzyme yield of FAEs is one of the primary factors limiting its application. Therefore, in this paper, we optimized the fermentation conditions for the expression of FAE BpFae^T132C-D143C with excellent thermal stability in Escherichia coli by experimental design. Firstly, we explored the effects of 11 factors such as medium type, isopropyl-β-D-thiogalactopyranoside (IPTG) concentration, and inoculum size on BpFae^T132C-D143C activity separately by the single factor design. Then, the significance of the effects of seven factors, such as post-induction temperature, shaker rotational speed, and inoculum size on BpFae^T132C-D143C activity, was analyzed by Plackett-Burman design. We identified the main factors affecting the fermentation conditions of E. coli expressing BpFae^T132C-D143C as post-induction temperature, pre-induction period, and post-induction period. Finally, we used the steepest ascent path design and response surface method to optimize the levels of these three factors further. Under the optimal conditions, the activity of BpFae^T132C-D143C was 3.58 U/ml, which was a significant 6.6-fold increase compared to the pre-optimization (0.47 U/ml), demonstrating the effectiveness of this optimization process. Moreover, BpFae^T132C-D143C activity was 1.52 U/ml in a 3-l fermenter under the abovementioned optimal conditions. It was determined that the expression of BpFae^T132C-D143C in E. coli was predominantly intracellular in the cytoplasm. This study lays the foundation for further research on BpFae^T132C-D143C in degrading agricultural waste transformation applications.