ReviewTools for the determination of population heterogeneity caused by inhomogeneous cultivation conditions

- Different components of biological noise lead to cell population heterogeneity.
- Physiological heterogeneity is affected under heterogeneous cultivation conditions.
- Novel on line and in situ methods allow the fast detection of population heterogeneity.

Population heterogeneity among a microbial culture can occur in various stages of a bioprocess. When a nutrient-limited fed-batch process is applied in the large scale, gradient formation (e.g. at the substrate concentration or the pH-value) can have a tremendous impact on the process performance. It might also have an impact on population heterogeneity, as the cells are opposed to stressful conditions that is an oscillating environment, when they pass the different zones evolved in the liquid phase. Nevertheless, the question whether these conditions support heterogeneity of a culture has not been clearly answered so far. Furthermore, if such a heterogeneity affects product formation, the usual analysis tools, which do not rely on a single-cell basis, certainly do not gain sufficiently suitable information for process optimization. This overview on the one hand provides information about the contribution of an oscillating environment to the formation of heterogeneities within a population and on the other hand a summary of tools, which can be used to investigate physiologic and morphologic heterogeneity during process development, scale up and production. If these techniques are considered, the identification of targets for accelerated process optimization on a single-cell basis becomes easier and faster.