Online Dissolved Oxygen Monitoring Uncovers Unique Metabolic Events in E.coli Fermentations

Metabolic oscillations refer to the periodic or cyclic fluctuations in the levels of metabolites or response in certain parameters, such as dissolved oxygen, within a biological system. Metabolic oscillations have been previously reported in a number of bioprocesses, including E. coli fermentations. In this study, dissolved oxygen levels were closely monitored using DO Sensor Pills in shake flask fermentations of E. coli, grown in three distinct complex media compositions: Plain lysogeny broth (LB) medium, LB medium with 0.2% additional glucose, and terrific broth (TB) medium with 0.2% glycerol.

Notably, oscillations in dissolved oxygen levels were observed, distinct for each complex medium fermentation and consistent within duplicates of the same medium. This suggests that metabolic pathway fluctuations are influenced by media compositions. 

Theories exist as to why these oscillations occur, with one prominent theory suggesting that occasional mismatches in amino acid profiles lead to rapid fluctuations in protein synthesis. When sugar is used for protein synthesis, oxygen is incorporated into cell protein rather than being respired to CO₂, resulting in less oxygen usage and explaining the oscillations in oxygen levels.

While the exact metabolic reasons for the observed oscillations are not fully understood and require further study, the close, real-time monitoring of oxygen levels provides valuable insights into when these oscillations occur, significantly contributing to our understanding of this phenomenon.

Notably, the dissolved oxygen profile throughout E.coli fermentations grown in different media compositions differ significantly, whereas duplicates grown in the same medium and under the same conditions show precisely the same dissolved oxygen profile. The addition of 0.2 % glucose led to longer oxygen limitation, compared to the LB medium without additional glucose. The TB glycerol medium culture on the other hand went into oxygen limitation later, but didn't recover until the end of the fermentation. This shows that the different media compositions have a pronounced effect on oxygen consumption throughout the E.coli fermentation. Due to the high data density derived from dissolved oxygen measurements with DOTS DO Sensor Pills, more detailed effects of the media on oxygen levels could be observed in addition. These metabolic oscillations were detected as reocurring peaks in cultures grown in LB medium at distinct timepoints. Although the precise metabolic causes of the observed oscillations remain unclear and warrant additional research, the close, real-time monitoring of oxygen levels offers valuable insights into the timing of these oscillations, greatly supporting research in this field.