AUTOMATED FED-BATCH FERMENTATION WITH FEEDBACK CONTROLS BASED ON DISSOLVED-OXYGEN (DO) AND PH FOR PRODUCTION OF DNA VACCINES

A fermentation process in Escherichia coli for production of supercoil ed plasmid DNA for use as a DNA vaccine was developed using an automat ed feed-back control nutrient feeding strategy based on dissolved oxyg en (DO) and pH. The process was further automated through a computer-a ided data processing system to regulate the cell growth rate by contro lling interactively both the nutrient feed rate and agitation speed ba sed on DO, The process increased the total yield of the plasmid DNA by approximately 10-fold as compared to a manual fed-batch culture, The final cell yield from the automated process reached 60 g L(-1) of dry cell weight (OD600 = 120) within 24 h, A plasmid DNA yield of 100 mg L (-1) (1,7 mg g(-1) cell weight) was achieved by using an alkaline cell lysis method, Plasmid yield was confirmed using High Performance Liqu id Chromatography (HPLC) analysis, Because cells had been grown under carbon-limiting conditions in the automated process, acetic acid produ ction was minimal (below 0.01 g L(-1)) throughout the fed-batch stage, In contrast, in the manual process, an acid accumulation rate as high as 0.36 g L(-1) was observed, presumably due to the high nutrient fee d rates used to maintain a maximum growth rate, The manual fed-batch p rocess produced a low cell density averaging 10-12 g L(-1) (OD600 = 25 -30) and plasmid yields of 5-8 mg L(-1) (approximately 0.7 mg g(-1) ce lls), The improved plasmid DNA yields in the DO- and pH-based feed-bac k controlled process were assumed to be a result of a combination of i ncreased cell density, reduced growth rate (CL) from 0.69 h(-1) to 0.1 3 h(-1) and the carbon/nitrogen limitation in the fed-batch stage. The DO- and pH-based feed-back control, fed-batch process has proven itse lf to be advantageous in regulating cell growth rate to achieve both h igh cell density and plasmid yield without having to use pure oxygen, The process was reproducible in triplicate fermentations at both 7-L a nd 80-L scales.