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

•First time application of in situ Microscopy to high density Escherichia coli cultivations.•An efficient image processing algorithm is presented to determine cell density in Escherichia coli cultivations.•Online access to cell concentration up 70g/L dry cell mass. 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%.