Effect of different aeration and polyethylene glycol concentration on growth of Escherichia coli DH5α in a 1L bioreactor

Large culture volume in bioreactor necessitates aeration for providing sufficient oxygen for cell growth. Thus, extend of aeration and amount of anti-foam needed for suppressing foam formation are key parameters determining the success of bioreactor fermentation. Specifically, while aeration provides more oxygen for powering cellular metabolism and could lead to faster growth rate and more efficient metabolism, it also introduces greater shear stress, mixing and foam formation. On the other hand, anti-foaming agents such as polyethylene glycol (PEG) could exert a toxicity effect on cells as well as introducing increased osmolarity and viscosity that could hamper cell growth. In this preliminary study, effect of different PEG concentrations and extent of aeration on growth of Escherichia coli DH5α (ATCC 53868) in a 1L bioreactor at 37 oC with LB Lennox growth medium was investigated. Experiment results revealed that E. coli DH5α growth in bioreactor at 1 VVM aeration with 1 g/L PEG was faster than that in a 250 mL glass shake flask, and with greater secretion of alkaline metabolites. Similar optical density obtained between bioreactor and shake flask cultivation pointed to the maximized utilization of growth medium nutrients for biomass formation. Increase in bioreactor aeration to 3 VVM at 1 g/L PEG, however, resulted in increased secretion of acidic metabolites into the culture broth while allowing similar maximal optical density to be obtained compared to aeration of 1 VVM at 1 g/L PEG. This indicated that E. coli DH5α was able to adapt to physiological impacts from increased aeration and highlighted that no significant metabolic energy was diverted from biomass formation. Finally, increase in PEG concentration to 10 g/L from 1 g/L did not introduce additional toxicity effect given that growth profile of E. coli DH5α under the two PEG concentrations overlapped each other. However, observations of reduced secretion of acidic metabolites at the outset of growth in 10 g/L PEG pointed to physiological impacts that did not affect growth rates and biomass formation. Collectively, E. coli DH5α was able to tolerate enhanced aeration of 3 VVM and 10 g/L PEG anti-foam without significant detrimental impacts on growth rates and biomass formation.