Unraveling the Antibacterial and Iron Chelating Activity of N-Oxide Hydroxy-Phenazine natural Products and Synthetic Analogs against Staphylococcus aureus

Phenazines are redox-active secondary metabolites produced by many microorganisms, especially by bacteria. These compounds are often produced at high cell densities in various niches. Pseudomonas strains are the most common phenazine producers, and phenazine production in these bacteria is controlled by quorum sensing, a mechanism that enables bacteria to collectively respond to changes in cell density. As phenazines exhibit a wide range of activities against many different species, this has led to increased interest and studies related to their mechanisms of action. In this work, we have investigated and evaluated the activity of an array of phenazine-based natural products and their analogs on Gram-positive bacteria that share the same natural niches with Pseudomonas, such as the human pathogen Staphylococcus aureus. This human pathogen plays a major role in lung infections and is often found in such infections together with P. aeruginosa. Among the screened compounds, hydroxyl-containing phenazines with a 5,10-dioxide scaffold were found to exhibit potent inhibitory effects on the growth of S. aureus. The natural product iodinin (1,6-dihydroxyphenazine 5,10-dioxide, 6), which was chosen as a model for this class of compounds has been found to strongly chelate iron (II), thus we examined the potential role of iron starvation in suppressing the growth of this pathogen by these phenazines that are generally linked to reactive oxygen species formation mechanisms. Our results suggest that chelation of essential metals, leading to a lack of important nutrients could have a significant contribution to the antibacterial activity of these phenazines, alongside with ROS production, DNA damage and oxidative stress.