An exploration of cheater dynamics during nitric oxide induced competition

Abstract

The growing prevalence of multidrug-resistant antibiotics is driving an urgent need for the development of new antimicrobial therapies, particularly ones which are less destructive to the gut microbiome and against which pathogens may develop resistance more slowly. Nitric oxide (NO•) is a powerful antimicrobial utilized by phagocytes of the innate immune system, to which a number of bacterial pathogens have developed detoxification defenses that are essential for their virulence. The identification of new therapeutic targets in this detoxification system could lead to the development of antivirulence therapies against these pathogens. This thesis explores the phenomenon of cheating in an NO•-induced competition assay. Stress-associated competitions can be used with high-throughput methods, such as transposon insertion sequencing, to identify novel genetic mediators; however, cheating stymies the capacity of such assays to do so. Cheating was demonstrated in cocultures of wild-type, NO•-tolerant, and NO•-sensitive mutants, in which sensitive mutants took advantage of NO• clearance by the tolerant mutants without themselves contributing to detoxification, reducing the capacity of the assay to discriminate between these mutants. We further explored several potential strategies for reducing cheating in cocultures in search of improved conditions under which to perform the competition assays to enhance differentiation between strains with differing NO• sensitivities.