Online monitoring of cell concentration in high cell density Escherichia coli cultivations using in situ Microscopy.

In situ Microscopy (ISM) is an optical non-invasive technique to monitor cells in bioprocesses in real-time. Escherichia coli is the most studied and used organism in biotechnology. In this article the cell density in Escherichia coli cultivations was monitored by applying ISM in these cultivations. The acquired images were analyzed with an image processing algorithm to determine the turbidity of the cultivation medium. In three cultivations the cell density was monitored with the algorithm and offline samples were taken to determine the dry cell mass (DCM). Both results were correlated and concentrations up to 70g/L DCM could be measured via ISM. For higher cell densities a saturation was recognized. The deviation of the calibration lines within three cultivations was 8%.

In situ microscopy for online monitoring of cell concentration in Pichia pastoris cultivations.

In situ Microscopy (ISM) is an optical non-invasive technique to monitor cells in bioprocesses in real-time. Pichia pastoris is one of the most promising protein expression systems. This yeast combines fast growth on simple media and important eukaryotic features such as glycosylation. In this work, the ISM technology was applied to Pichia pastoris cultivations for online monitoring of the cell concentration during cultivation. Different ISM settings were tested. The acquired images were analyzed with two image processing algorithms. In seven cultivations the cell concentration was monitored by the applied algorithms and offline samples were taken to determine optical density (OD) and dry cell mass (DCM). Cell concentrations up to 74g/L dry cell mass could be analyzed via the ISM. Depending on the algorithm and the ISM settings, an accuracy between 0.3 % and 12 % was achieved. The overall results show that for a robust measurement a combination of the two described algorithms is required.