Production of cyclic adenosine monophosphate by Arthrobacter sp. A302 using fed-batch fermentation with pH-shift control

The production of cyclic adenosine monophosphate (cAMP) by Arthrobacter sp. A302 was studied in a 5 L stirred tank fermentor under a range of pH values (6. 5-8. 0) and glucose feeding rates. In batch fermentation under a controlled pH, the optimum pH for cell growth was 7. 5 with dry cell density (X) of 11. 43 g L, and the optimum pH for cAMP accumulation was 7. 0 with cAMP concentration of 7. 41 g L. In order to achieve the high X and cAMP yield simultaneously, a pH-shift control strategy was proposed based on kinetic analysis of specific cell growth rate (μ) and specific cAMP formation rate (q_s). In this method, pH was controlled to 7. 0 for the first 30 h of fermentation, and then subsequently shifted to 7. 5 and maintained until the end of the process. Application of this approach significantly enhanced the cAMP concentration. Thereafter, cAMP production was further improved by combining the above-mentioned pH-control system and fed-batch process with glucose at a constant feeding rate of 1. 0 g L^-1h^-1. Under optimum conditions, the final cAMP production was 10. 87 g L, which is 110. 0, 46. 7, and 27. 7% higher than that of the pH-uncontrolled, pH-controlled, and pH-shift controlled methods, respectively.