(623e) Escherichia coli Nitric Oxide Detoxification Is Robust to Nitrogen Starvation

Within phagosomal environments, numerous factors that include acidification, reactive oxygen species, reactive nitrogen species, and nutrient deprivation contribute to pathogen demise. Concomitantly, pathogenic bacteria have evolved defense systems to cope with phagosomal stressors, which include enzymes that detoxify nitric oxide (NO). A deeper understanding of how those defense systems are deployed under adverse conditions that mimic key elements of phagosomes will facilitate targeting of those systems for therapeutic purposes. Here we investigate how E. coli detoxifies NO in the absence of useable nitrogen. Nitrogen availability is limited in phagosomes due to the removal of nitrogenous compounds (e.g., amino acids) from phagosomes. We hypothesized that nitrogen starvation would impair the capacity of E. coli to detoxify NO because it depresses translation rates and the main defense enzyme used by E. coli, Hmp, is synthesized de novo in response to NO stress. However, we found that E. coli detoxifies NO at the same rate regardless of whether useable nitrogen was present. We confirmed that the nitrogen in NO could not be used by E. coli under our experimental conditions, and we discovered that the metabolic effects of NO supersede those of nitrogen starvation. Interestingly, E. coli does not consume measurable nitrogen during NO stress despite the need to translate defense enzymes. Further, we identified RelA as a transcriptional regulator that was critical to the robustness of NO detoxification under nitrogen starvation. These data demonstrate that E. coli is well poised to detoxify NO in the absence of useable nitrogen and suggest that the stringent response could be a useful target for the development of anti-virulence therapies against pathogens that need to defend themselves against NO to propagate infections.