L-cysteine is a sulphur-containing amino acid used in the manufacture of many products such as food supplements, cosmetics, and medicines. The industrial production of this amino acid can be done with microorganisms such as Escherichia coli, which is an environmentally friendly alternative.

However, on an industrial scale, gradients occur in the bioreactor, which in turn can lead to the formation of population heterogeneities in the production process. This complicates scale-up, as production output can change unpredictably.

In-vivo-measurements of population heterogeneities are possible with fluorescent marker proteins that can indicate important individual cell properties such as growth rate, stress response and oxygen limitation, as well as product formation. The different fluorescence signals of the individual microorganisms can be measured at-line using a flow cytometer with automatic sample preparation. Population heterogeneities can thus be identified in real-time, and it can be investigated, for example, by which interventions during the process population heterogeneities can be controlled.

The aim of this research project is to carry out the feed process for L-cysteine production with Escherichia coli in a multi-compartment bioreactor on a laboratory scale to be able to analyse the effects of gradients caused by long mixing times on an industrial scale. For this purpose, the properties of the microorganisms are measured automatically in real time as a function of the process time with an at-line flow cytometer to be able to directly detect the emergence of population heterogeneities. Interesting subpopulations can be separated with a cell sorter and characterised in more detail.