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Cooperation and competition : studies on heterogeneous microbial cultures


Schmidt,  J. K.
Bioprocess Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Max Planck Society;

Reichl,  U.
Otto-von-Guericke-Universität Magdeburg;
Bioprocess Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Max Planck Society;

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Schmidt, J. K., König, B., & Reichl, U. (2003). Cooperation and competition: studies on heterogeneous microbial cultures. Poster presented at Jahrestagung der Vereinigung für allgemeine und angewandte Mikrobiologie (VAAM), Berlin, Germany.

Bacteria growing in a natural environment often do not occur as pure but as mixed cultures presumably forming complex networks. Knowledge of interactions within heterogeneous microbial systems is of increasing interest and necessary for comprehension of impact mechanisms in technical, medical or ecological fields. Microbial communities in vivo are difficult to approach for experimental characterisation due to complex and incompletely identifiable influencing factors. On the other hand results from pure culture studies in laboratory cannot be transferred to community mode of growth. We chose a model-system of several bacterial species, e.g. Pseudomonas aeruginosa, Burkholderia cepacia and Stenotrophomonas maltophilia to study their interactions and general behaviour under competitive conditions. One of our aims is to investigate growth dynamics of heterogeneous microbial communities, e.g. to search for possible equilibrium points (coexistence) as these can commonly be found in nature, but are difficult to be achieved and investigated in vitro. Mathematical modelling is an approach we use, e.g. to better understand differences between observations of laboratory and in vivo cultures. Applying an improved T-RFLP method based on the adaptation of T-RFLP analysis of 16S rRNA gene fragments to an automated multi-capillary sequence analyser (Abi Prism 3100, Applied Biosystems) [1] allows rapid qualitative as well as quantitative analysis of biomass in mixed-culture samples. Didderent bioreactors, e.g. stirred-tanks (2L and 500mL) and shaking flasks, will be compared concerning their suitability to establish a culture-method for generation of reproducible community cultures. Process control system of stirred-tank bioreactors will by used to realize defined culture conditions and analyse dependency on process parameters. Here we report the comparison between growth characteristics of each bacteria species resulting from pure and mixed culture analysis. Focus will be on shaking flask and small scale stirred-tank reactor cultures. Influence of parameters such as oxygen-supply, nutrient-limitation and pH-value on physiological performance and competitive bacterial behaviour in our model-system will be outlined. [1] Trotha R. et al. (2002); Electrophoresis 23(7-8):1070-79