Elucidating principles of bacterial nitric oxide metabolism to pave the way for novel antibiotics

Abstract

Antibiotics have revolutionized medicine since the 20th century and transformed the way we treat and prevent bacterial infections. However, the current arsenal of antibiotics has lost efficacy, as antimicrobial resistance has developed and become prevalent across diverse bacterial species. With the growing list of resistant microbes and a weak pipeline of antibiotics, the need for development of alternative therapies to combat bacterial infections has never been higher. One promising strategy is to assist the innate immune response by disrupting bacterial defense systems used against it. Nitric oxide (NO) is one of the main weapons used by immune cells to neutralize pathogens within phagosomes. NO has broad-spectrum activity and the importance of NO to pathogen virulence has been demonstrated by the large number of bacteria that require NO detoxification systems to establish or propagate infections. Targeting of these defense networks could illuminate novel therapeutic avenues for the treatment of bacterial infections. In my doctoral thesis, we explored several aspects of NO metabolism in bacteria. First, we investigated how delivery dynamics influence the antimicrobial potency of NO on Escherichia coli. Using a hybrid approach that involved both computational and experimental methodologies, we found that the important design parameter, when delivering NO, was to maximize the duration of respiratory inhibition to achieve the longest period of bacteriostasis. Next, we found that transcript cleavage factors (GreA and GreB) play an important regulatory role in E. coli NO detoxification. Interestingly, we discovered that cells lacking GreA and GreB undergo a phenotypic diversification in response to NO challenge, in which two subpopulations exhibit distinct levels of transcriptional activity. Lastly, we found that Pseudomonas aeruginosa prioritizes H2O2 detoxification over NO when faced with both stresses simultaneously, which mirrors the detoxification pattern exhibited by E. coli. The work in this thesis contributes to the growing knowledgebase surrounding how pathogens sense and respond to phagosome antimicrobials, and provides novel information to consider when developing next generation antimicrobial therapies.