IST Austria Thesis
Antibiotics have diverse effects on bacteria, including massive changes in bacterial gene expression. Whereas the gene expression changes under many antibiotics have been measured, the temporal organization of these responses and their dependence on the bacterial growth rate are unclear. As described in Chapter 1, we quantified the temporal gene expression changes in the bacterium Escherichia coli in response to the sudden exposure to antibiotics using a fluorescent reporter library and a robotic system. Our data show temporally structured gene expression responses, with response times for individual genes ranging from tens of minutes to several hours. We observed that many stress response genes were activated in response to antibiotics. As certain stress responses cross-protect bacteria from other stressors, we then asked whether cellular responses to antibiotics have a similar protective role in Chapter 2. Indeed, we found that the trimethoprim-induced acid stress response protects bacteria from subsequent acid stress. We combined microfluidics with time-lapse imaging to monitor survival, intracellular pH, and acid stress response in single cells. This approach revealed that the variable expression of the acid resistance operon gadBC strongly correlates with single-cell survival time. Cells with higher gadBC expression following trimethoprim maintain higher intracellular pH and survive the acid stress longer. Overall, we provide a way to identify single-cell cross-protection between antibiotics and environmental stressors from temporal gene expression data, and show how antibiotics can increase bacterial fitness in changing environments. While gene expression changes to antibiotics show a clear temporal structure at the population-level, it is unclear whether this clear temporal order is followed by every single cell. Using dual-reporter strains described in Chapter 3, we measured gene expression dynamics of promoter pairs in the same cells using microfluidics and microscopy. Chapter 4 shows that the oxidative stress response and the DNA stress response showed little timing variability and a clear temporal order under the antibiotic nitrofurantoin. In contrast, the acid stress response under trimethoprim ran independently from all other activated response programs including the DNA stress response, which showed particularly high timing variability in this stress condition. In summary, this approach provides insight into the temporal organization of gene expression programs at the single-cell level and suggests dependencies between response programs and the underlying variability-introducing mechanisms. Altogether, this work advances our understanding of the diverse effects that antibiotics have on bacteria. These results were obtained by taking into account gene expression dynamics, which allowed us to identify general principles, molecular mechanisms, and dependencies between genes. Our findings may have implications for infectious disease treatments, and microbial communities in the human body and in nature.
First of all, I would like to express great gratitude to my PhD supervisor Tobias Bollenbach. Through his open and trusting attitude I had the freedom to explore different scientific directions during this project, and follow the research lines of my interest. I am thankful for constructive and often extensive discussions and his support and commitment during the different stages of my PhD. I want to thank my committee members, Călin Guet, Terry Hwa and Nassos Typas for their interest and their valuable input to this project. Special thanks to Nassos for career guidance, and for accepting me in his lab. A big thank you goes to the past, present and affiliated members of the Bollenbach group: Guillaume Chevereau, Marjon de Vos, Marta Lukačišinová, Veronika Bierbaum, Qi Qin, Marcin Zagórski, Martin Lukačišin, Andreas Angermayr, Bor Kavčič, Julia Tischler, Dilay Ayhan, Jaroslav Ferenc, and Georg Rieckh. I enjoyed working and discussing with you very much and I will miss our lengthy group meetings, our inspiring journal clubs, and our common lunches. Special thanks to Bor for great mental and professional support during the hard months of thesis writing, and to Marta for very creative times during the beginning of our PhDs. May the ‘Bacterial Survival Guide’ decorate the walls of IST forever! A great thanks to my friend and collaborator Georg Rieckh for his enthusiasm and for getting so involved in these projects, for his endurance and for his company throughout the years. Thanks to the FriSBi crowd at IST Austria for interesting meetings and discussions. In particular I want to thank Magdalena Steinrück, and Anna Andersson for inspiring exchange, and enjoyable time together. Thanks to everybody who contributed to the cover for Cell Systems: The constructive input from Tobias Bollenbach, Bor Kavčič, Georg Rieckh, Marta Lukačišinová, and Sebastian Nozzi, and the professional implementation by the graphic designer Martina Markus from the University of Cologne. Thanks to all my office mates in the first floor Bertalanffy building throughout the years: for ensuring a pleasant working atmosphere, and for your company! In general, I want to thank all the people that make IST such a great environment, with the many possibilities to shape our own social and research environment. I want to thank my family for all kind of practical support during the years, and my second family in Argentina for their enthusiasm. Thanks to my brother Bernhard and my sister Martina for being great siblings, and to Helena and Valentin for the joy you brought to my life. My deep gratitude goes to Sebastian Nozzi, for constant support, patience, love and for believing in me.
Mitosch K. Timing, Variability and Cross-Protection in Bacteria – Insights from Dynamic Gene Expression Responses to Antibiotics. IST Austria; 2017. doi:10.15479/AT:ISTA:th_862
Mitosch, K. (2017). Timing, variability and cross-protection in bacteria – insights from dynamic gene expression responses to antibiotics. IST Austria. https://doi.org/10.15479/AT:ISTA:th_862
Mitosch, Karin. Timing, Variability and Cross-Protection in Bacteria – Insights from Dynamic Gene Expression Responses to Antibiotics. IST Austria, 2017. https://doi.org/10.15479/AT:ISTA:th_862.
K. Mitosch, Timing, variability and cross-protection in bacteria – insights from dynamic gene expression responses to antibiotics. IST Austria, 2017.
Mitosch K. 2017. Timing, variability and cross-protection in bacteria – insights from dynamic gene expression responses to antibiotics, IST Austria, 113p.
Mitosch, Karin. Timing, Variability and Cross-Protection in Bacteria – Insights from Dynamic Gene Expression Responses to Antibiotics. IST Austria, 2017, doi:10.15479/AT:ISTA:th_862.
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Part of this Dissertation