Impact of Elevated Levels of Dissolved CO 2 on Performance and Proteome Response of an Industrial 2'-Fucosyllactose Producing Escherichia coli Strain.

Large-scale microbial industrial fermentations have significantly higher absolute pressure and dissolved CO 2 concentrations than otherwise comparable laboratory-scale processes. Yet the effect of increased dissolved CO 2 (dCO 2 ) levels is rarely addressed in the literature. In the current work, we have investigated the impact of industrial levels of dCO 2 (measured as the partial pressure of CO 2 , pCO 2 ) in an Escherichia coli -based fed-batch process producing the human milk oligosaccharide 2'-fucosyllactose (2'-FL). The study evaluated the effect of high pCO 2 levels in both carbon-limited (C-limited) and carbon/nitrogen-limited (C/N-limited) fed-batch processes. High-cell density cultures were sparged with 10%, 15%, 20%, or 30% CO 2 in the inlet air to cover and exceed the levels observed in the industrial scale process. While the 10% enrichment was estimated to achieve similar or higher pCO 2 levels as the large-scale fermentation it did not impact the performance of the process. The product and biomass yields started being affected above 15% CO 2 enrichment, while 30% impaired the cultures completely. Quantitative proteomics analysis of the C-limited process showed that 15% CO 2 enrichment affected the culture on the protein level, but to a much smaller degree than expected. A more significant impact was seen in the dual C/N limited process, which likely stemmed from the effect pCO 2 had on nitrogen availability. The results demonstrated that microbial cultures can be seriously affected by elevated CO 2 levels, albeit at higher levels than expected.