Population heterogeneity describes the diverse behaviour of cells of an isogenic culture in bioprocesses. This phenomenon especially arises in bioreactors of industrial scale due to the occurrence of inhomogeneity. A better understanding of the mechanisms behind the formation of population heterogeneity could support future scale-up procedures from homogeneous laboratory bioreactors to large-scale production processes.

The aim of this research project is the investigation of process conditions leading to the formation of subpopulations in a fed-batch process with E. coli converting glycerol to L-phenylalanine at laboratory scale. Gradients can be generated in laboratory scale by the application of a two-compartment reactor consisting of a stirred-tank reactor coupled to a plug flow reactor in by-pass. Thus, microorganisms can be exposed to different gradients like substrate deficiency or excess inside the plug flow reactor. 

To monitor the formation of subpopulations in bioprocesses in vivo, an L-phenylalanine producing E. coli reporter strain shall be used. For that, the expression of fluorescent proteins are coupled to specific cellular properties allowing the screening of growth rate, general stress response, oxygen availability and the product formation of single cells. The expressed fluorescence of the producing cells at different process conditions can be analyzed by flow cytometry and occurring subpopulations can be isolated and further characterized with a cell sorter.