Dynamic Metabolic Flux Analysis Demonstrated on Cultures Where the Limiting Substrate Is Changed from Carbon to Nitrogen and Vice Versa

摘要

The main requirement for metabolic flux analysis (MFA) is that thecells are in a pseudo-steady state, that there is no accumulation or depletion of intracellular metabolites. In thepast, the applications of MFA were limited to the analysis of continuous cultures. This contribution introduces the concept ofdynamic MFA and extends MFA so that it is applicable to transient cultures. Time series of concentration measurements aretransformed into flux values. This transformation involves differentiation, which typically increases the noisiness of thedata. Therefore, a noise-reducing step is needed. In this work, polynomial smoothing was used. As a test case, dynamic MFA is applied on Escherichia coli cultivations shifting from carbon limitation to nitrogen limitation and vice versa. After switching the limiting substrate from N to C, a lag phase was observed accompanied with an increase in maintenanceenergy requirement. This lag phase did not occur in the C- to N-limitation case.