Nitric oxide tunes secreted metabolite bioactivity

The radical nitric oxide ({middle dot}NO) is short-lived but has imprinted itself on many aspects of physiology and disease. {middle dot}NOs rapid production and consumption, coupled with its intrinsic reactivity, drive its biological importance; thus, defining mechanisms and targets of {middle dot}NO reactivity is necessary to assess its fate and impact. Cellular small molecules are a major class of {middle dot}NO-reactive targets, possessing a variety of molecular functionalities that can react with {middle dot}NO. Yet the capacity for secreted small molecules to react with {middle dot}NO, as well as the biological consequences of such reactivity, have received little attention. Here, we explore the reactivity of {middle dot}NO with phenazine metabolites, microbially-derived secreted small molecules that possess antibiotic properties and can modulate their microenvironment. Using Pseudomonas aeruginosa as a model phenazine producer, we find that {middle dot}NO reacts with specific phenazines to yield stable, chemically-distinct products. These chemical transformations significantly attenuate phenazine antibiotic properties, including against the phenazine nonproducer Staphylococcus aureus, a competitor with P. aeruginosa for niches in the context of infection. By contrast, P. aeruginosa experiences rapid loss in viability when phenazines and {middle dot}NO react. This toxicity occurs even in the presence of S. aureus, which displays resistance to nitrosylated phenazines, implicating a specific toxicity dependent on the formation of the phenazine-NO adduct. These findings highlight the capacity of {middle dot}NO to transform metabolite activity and suggest that {middle dot}NO can tune microbial interactions in complex environments by a mechanism of action hitherto unappreciated.