Non-invasive monitoring of bacterial growth and auto-induced protein production in a bioreactor with a closed-loop GC-IMS

In numerous applications biomass or biochemically active substances, like pharmaceuticals, flavors or bio-ethanol, are produced in industrial-scale bioreactors. In order to ensure a constant and high quality and quantity of the particular product the biochemical environment within the reactor needs to be continuously controlled within narrow limits. Thus, sensitive sensor systems that allow continuous and preferably non-invasive monitoring of relevant parameters during the cultivation are required. In this work we present results of an analysis of exhaust gas of a bioprocess composed of growing phase and auto-inductive protein production phases of a recombinant Escherichia coli BL21 strain as model organism using a compact closed-loop ion mobility spectrometer (IMS) with gas chromatographic (GC) pre-separation. The used GC-IMS (in-house development) has a mobility resolution of about R=90 (IMS drift time / peak width) and enables automatic sampling and analysis of the exhaust gas every 20 min. We compare the intensity of different IMS peaks with additional online and offline data like oxygen consumption, optical density or the fluorescence of a GFP-labeled protein which is produced by the organism after auto-induction. A great challenge in this context is to detect trace concentrations of possible precursors for a metabolic change or indicators for the efficiency of such a change in the presence of very high concentrations of water and compounds like acetone, ethanol and ammonia. Besides multiple peaks that show a significant and reproducible change during the cultivation we observe at least one peak that is assumed to be a precursor for the induction process.