Weiterentwicklung einer Methode zur Bestimmung von Atmungsraten in geschüttelten Bioreaktoren
- Improvement of a method for determination of respiration activities in shaken bioreactors
Hansen, Sven; Büchs, Jochen (Thesis advisor)
Aachen : Publikationsserver der RWTH Aachen University (2013)
Dissertation / PhD Thesis
Aachen, Techn. Hochsch., Diss., 2012
The Respiration Activity MOnitoring System (RAMOS) is an established device to measure on-line the oxygen transfer rate (OTR), thereby, yielding relevant information about metabolic activities of microorganisms and cells during shake flask fermentations. For very fast-growing microbes, however, the RAMOS technique provides too few data points for the OTR. Thus, this current study presents a new model based evaluation method for generating much more data points to enhance the precision of OTR measurements. The conventional method of calculating OTR in RAMOS is inadequate and, hence, not suitable for raising the data density of the OTR. Instead of assuming a steady state the new calibration strategy also considers the dynamic behavior of the gas headspace volume. By applying a complete oxygen headspace balance and data approximation methods a higher data density can be generated. Cultivations with E. coli BL21 pRSET eYFP-IL6 have shown that short diauxic and even triauxic metabolic activities can be detected with much more detail compared to the conventional evaluation. During oxygen limitations, a decline of the OTR during the stop phases, which occur when the inlet and outlet valves of the RAMOS flask are closed for calibrating the oxygen sensor, were also detected. These declines reflect a reduced oxygen transfer due to the stop phases. In contrast to the conventional calculation method the new method is almost independent from the number of stop phases chosen in the experiments. This new calculation method unveils new peaks of metabolic activity which otherwise would not have been resolved by the conventional RAMOS evaluation method. The new method yields substantially more OTR and CTR data points, thereby, enhancing the information content and the precision of the measurements. Furthermore, short oxygen limitations can be detected by a decrease of the OTR during the stop phases.