Quantitative experimental characterization and mathematical modeling of mixed culture dynamics

Traditional laboratory methodology uses pure cultures for strain characterization. A transfer of findings from such experiments to describe growth in the presence of other species is hardly possible. The limitation is the lack of characterization and knowledge of interaction mechanisms both inside the community and also outside with its environment, which still have to be understood. For example competition might take place, which can be direct (interference competition) or indirect (resource competition). The first could be formation of an inhibitor by one species the latter could be competition for the same substrate. An important prerequisite for studies on mixed cultures is the monitoring of the population dynamics to obtain quantitative data. Cell numbers and relevant metabolites should be monitored. Up to now, in contrast to numerous theoretical considerations on the dynamics of mixed cultures based on mathematical models, complex microbial communities have hardly been studied in laboratories, as cell quantification methods and protocols for defined mixed cultivations are not available. Therefore, quantitative experimental data for validation of such models are hardly reported for more than two species. In particular, studies of bacterial population dynamics with absolute cell numbers of more than two species are rare. The aim of the presented work was the establishment of a methodology for quantitative analysis of a bacterial mixed culture consisting of at least three species. The focus was on identification of interactions of species with arbitrary and rather unknown growth characteristics. A new approach using the comparison of experiment and model simulation was applied on selected strains from the CF context as a model mixed culture.