Optimization of a mini-scale chemostat system for the analysis of metabolic flux distributions in stressed Bacillus Subtilis

This thesis focuses on the metabolic aspects of cellular adaptation processes to oxidative and iron limiting stresses. These stress conditions are generally encountered by pathogenic species upon the invasion of host organisms. It has attracted the attention of researchers and resulted in the initiation of a European project on Bacillus subtilis systems biology. This project aims at elucidating the regulatory pathways of B. subtilis under oxidative and iron stress for the subsequent application to pathogens. The present study attempts to identify and quantify the adaptations in central carbon metabolism in response to imposed stresses. Therefore a recently developed system of mini-chemostats is used as a culturing system. This setup allows a quick and economic way of culturing under many different conditions. The main finding in oxidative stress adaptations is the re-routing of carbon through the pentose phosphate pathway in order to generate NADPH. NADPH is used by processes that relief the cells of oxidative stress. Next to the production of reduction equivalents, there was an increased amount of extracellular TCA cycle intermediates as fumarate and succinate. The fluxes through this pathway did not change. The iron limitation experiments yielded less clear results on the impact on metabolism. This might be due to the chosen method to deferrate the medium. Deferoxamine caused only minor iron stress and was not life threatening for the cells. That the cells were only slightly affected was shown by the increased production of siderophores, bacterial iron harvesting compounds. The cells were able to survive the situation by the production of siderophores. The results of this study aid the BaSysBio project in obtaining a better understanding of B subtilis adaptation to a shift in environmental conditions. The generated data gives further insight into the adaptation processes and help model development by providing quantitative information on the stress responses. The results can be processed by BaSysBio and can eventually result in new strategies to combat pathogenic bacteria.BioprocesstechnologyBiotechnologyApplied Science