Bioreactor operation parameters as tools for metabolic regulations in fermentation processes: influence of pH conditions

The influence of controlled- and uncontrolled-pH conditions together with the initial pH on the product and by-product distributions and oxygen transfer characteristics, whereupon the process rate limitations in relation to the intracellular reaction rates were investigated in serine alkaline protease (SAP) fermentation process by recombinant Bacillus licheniformis carrying pHV1431::subC on a defined medium with the sole carbon source glucose in the pH range of 6.80–7.25 in batch bioreactors. Although the same amount of cell was produced at all the conditions in each type of operation, with the increase of initial pH the cell formation rates increased; moreover, uncontrolled-pH operation was favourable for the cell formation. The SAP synthesis rates and concentrations were higher at uncontrolled-pH operations. Among the fermentations, pH0=7.10 uncontrolled-pH operation produced maximum SAP activity that was ca. 900 Ucm^-3 at t=21 h. According to the biomass and SAP production profiles, bioprocess was divided into two periods; Period I (0