¹Binzhou Key Laboratory of Synthetic Biotechnology, Shandong Binzhou Animal Science and Veterinary Research Academy, Binzhou 256600, CHINA
²School of Life Science, NingXia University, Yinchuan, NingXia 750021, CHINA DOI : 10.9775/kvfd.2026.36550 Infectious bursal disease (IBD), caused by infectious bursal disease virus (IBDV), severely endangers the global poultry industry. The VP2 subunit vaccine represents a primary strategy for the prevention and control of IBD. Escherichia coli is widely used for recombinant VP2 production; however, acetate overflow during fermentation severely inhibits cell growth and target protein synthesis. Additionally, conventional constant-pH strategies and empirical pH regulation approaches fail to achieve a balance between high cell density, low by-product accumulation, and efficient expression of active VP2 protein. This study aimed to investigate the effects of various ions from pH regulators on the growth of the engineered strain E. coli 0125. Aqueous ammonia (NH₃·H₂O) was identified as the optimal regulator. Based on real-time monitoring of dissolved oxygen (DO) dynamics, the optimal pH for strain growth was determined to be 7.2. Subsequently, nine staged pH control strategies were established to optimize the fermentation process. The optimal protocol was to maintain the pH at 7.2 during the initial 0-6 h of fermentation, followed by adjustment to pH 6.8 during 6-12 h using NH₃·H₂O. Under these conditions, the wet cell concentration reached 28.37 g/L, the specific VP2 titer increased to 96 U/g, and acetate content was maintained at a low level of 2.19 g/L (P<0.05). Compared with the group maintained at pH 7.0 using sodium hydroxide, the total VP2 titer of the optimized group increased by 2.95 times. This refined staged pH control strategy effectively resolves the contradictions in E. coli fermentation and provides a practical technical approach for the large-scale industrial production of IBDV VP2 subunit vaccines. Keywords : Acetate, Escherichia coli, IBDV, pH regulation, VP2 protein