All aerobically growing microbes must deal with oxidative stress from intrinsically-generated reactive oxygen species (ROS), or from external ROS in the context of infection. To study the systems biology of microbial ROS response, we developed a genome-scale model of proteome damage and maintenance in response to ROS, by extending a genome-scale metabolism and macromolecular expression (ME) model of E. coli. This OxidizeME model recapitulated measured microbial oxidative stress response including metalloenzyme inactivation by ROS and amino acid auxotrophies. OxidizeME also correctly predicted differential expression under ROS stress. We used OxidizeME to investigate how environmental context affects the flexibility of ROS stress response. The context-dependency of microbial stress response has important implications for infectious disease. OxidizeME provides a computational resource for model-driven experiment design in this direction.The human immune system includes phagocytes that use reactive oxygen species (ROS) to combat pathogens. Most microbes are considerably weakened by this oxidative stress, whereas certain pathogens can grow inside the phagosome [1]. How microbes, including pathogens, evolve to tolerate such intense oxidative stress remains a long-standing question. To answer it requires a systemslevel understanding of the many interlinked biochemical and physiological adaptations for responding to ROS damage. Here, we approach this question through in silico experiments subjecting E. coli to varying degrees of oxidative stress in a multitude of environments. To this end, we extended a genome-scale model of E. coli metabolism and protein expression by incorporating ROS damage and response mechanisms.By their chemical nature, ROS can react with a broad array of macromolecules, often with deleterious consequences. In particular, a number of protein targets of ROS have been experimentally verified in detail; however, most of the potential targets of ROS have not been characterized individually. Thus, to better understand ROS stress, we must answer two questions: which biomolecules are damaged to what extent, and what is the cellular response to this damage? Here, we address these questions, focusing on ROS damage to metalloproteins. To predict cellular response to damage, we developed a novel model called OxidizeME. OxidizeME accounts for ROS damage to iron and iron-sulfur cluster cofactors of over 40 enzymes. We also modeled enzyme-catalyzed repair of oxidized iron-sulfur clusters. OxidizeME is able to predict cellular response at the metabolic and gene expression levels.
RESULTSA multiscale model of reactive oxygen species damage and response.We developed the OxidizeME model by extending the iLE1678-ME model of E. coli Metabolism and macromolecular Expression (ME model) [2] to account for damage to proteins by ROS, and cellular response mechanisms (Fig. 1) For each protein, OxidizeME computes the the fraction of inactivated enzyme due to cofactor oxidation as a function of intracellular ROS concentrati...