title: Evolution of Escherichia coli for maximum HOCl resistance through constitutive expression of the OxyR regulon.
abstract: Exposure of cells to stress impairs cellular functions and may cause killing or adaptation. Adaptation can be facilitated by stress-induced mutagenesis or epigenetic changes, i.e. phenotypic variation without mutations. Upon exposure to HOCl, which is produced by the innate immune system upon bacterial infection, bacteria trigger stress responses that enable increased survival against the stress. Here, we addressed the question whether bacteria can adapt to high HOCl doses and if so, how the acquired resistance is facilitated. We evolved Escherichia coli cells for maximum HOCl resistance by successively increasing the HOCl concentration in the cultivation medium. HOCl-resistant cells showed broad stress resistance but did not carry any chromosomal mutations as revealed by whole-genome sequencing. According to proteome analysis and analysis of transcript levels of stress-related genes, HOCl resistance was accompanied by altered levels of outer-membrane proteins A, C, F and W, and, most prominently, a constitutively expressed OxyR regulon. Induction of the OxyR regulon is facilitated by a partially oxidized OxyR leading to increased levels of antioxidant proteins such as Dps, AhpC/AhpF and KatG. These changes were maintained in evolved strains even when they were cultivated without stress for a prolonged time, indicating epigenetic changes contributed to stress resistance. This indicated that maximum HOCl resistance was conferred by the accumulated action of the OxyR stress response and other factors such as altered levels of outer-membrane proteins.
authors.affiliation: Center for Integrated Protein Science Munich, Department Chemie, Technische Universität München, 85747 Garching, Germany.
authors.forename: Jasmin
authors.initials: J
authors.lastname: Gundlach
authors.affiliation: Center for Integrated Protein Science Munich, Department Chemie, Technische Universität München, 85747 Garching, Germany.
authors.forename: Jeannette
authors.initials: J
authors.lastname: Winter
mesh_terms: D005075:Biological Evolution; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D006861:Hydrogen Peroxide / Q000378:metabolism*; D018384:Oxidative Stress; D018085:Regulon; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D012097:Repressor Proteins; C499299:oxyR protein, E coli; D006861:Hydrogen Peroxide