Population heterogeneity is eminently present in industrial scale bioprocesses and defined as the unequal behaviour of cells of an isogenic population. Due to insufficient mixing in technical bioreactors, gradients in for instance substrate concentration arise, so that cells encounter various microenvironments at different locations in the reactor. Since not all of the cells follow the same path and can react differently, a heterogeneous cell population emerges as function of process time. Consequently, lowered yields and increased by-product formation can be found in comparison to (ideally mixed) laboratory scale cultivations.

The aim of this Junior Research Group is the characterisation of population heterogeneity that arises in technical scale bioprocesses. Hereby, population heterogeneity is going to be on the one hand experimentally generated in laboratory scale reactors and on the other hand the development of subpopulations is analytically investigated. The overall goal is to achieve a better quantitative understanding of population heterogeneities, their causes and their control.

For that purpose, population heterogeneity manifested in distributions of single cell properties, will be studied under different industrially relevant cultivation conditions using Escherichia coli. Different cellular reporter systems will be employed to be able to follow the development and temporal course of population heterogeneity in vivo. In reporter systems, the expression of varying fluorescent reporter proteins is coupled to a cellular property in a way that for instance growth rates of single cells are visualized as fluorescence distribution. These distributions can then be detected using flow cytometry. Hence, temporal changes in e.g. the distribution of growth rates, product formation rates and/or other metabolic properties of cell populations in bioreactors with differences in mixing efficiency can be monitored throughout a bioprocess.