Pyocyanin Alters Redox Homeostasis and Carbon Flux through Central Metabolic Pathways in Pseudomonas aeruginosa PA14

Abstract

The opportunistic pathogen Pseudomonas aeruginosa produces colorful, redox-active antibiotics called phenazines. Excretion of pyocyanin, the best-studied natural phenazine, is responsible for the bluish tint of sputum and pus associated with P. aeruginosa infections in humans. Although the toxicity of pyocyanin for other bacteria, as well as its role in eukaryotic infection, has been studied extensively, the physiological relevance of pyocyanin metabolism for the producing organism is not well understood. Pyocyanin reduction by P. aeruginosa PA14 is readily observed in standing liquid cultures that have consumed all of the oxygen in the medium. We investigated the physiological consequences of pyocyanin reduction by assaying intracellular concentrations of NADH and NAD ؉ in the wild-type strain and a mutant defective in phenazine production. We found that the mutant accumulated more NADH in stationary phase than the wild type. This increased accumulation correlated with a decrease in oxygen availability and was relieved by the addition of nitrate. Pyocyanin addition to a phenazine-null mutant also decreased intracellular NADH levels, suggesting that pyocyanin reduction facilitates redox balancing in the absence of other electron acceptors. Analysis of extracellular organic acids revealed that pyocyanin stimulated stationary-phase pyruvate excretion in P. aeruginosa PA14, indicating that pyocyanin may also influence the intracellular redox state by decreasing carbon flux through central metabolic pathways.

Discovery of a biofilm electrocline using real-time 3D metabolite analysis

“…Indeed, reduced PYO displays significant antimicrobial activity (27) and the ability to reduce insoluble Fe 3+ to soluble Fe 2+ (32), whereas the oxidized form can potentially function as an alternative electron acceptor (33,34). Thus, to understand the biological function of PYO, it would be valuable not only to measure PYO concentration, but also the PYO redox state.…”

“…To examine this question, biofilms of P. aeruginosa Δphz1/2, a strain unable to produce phenazines because of deletion of both phz biosynthetic operons (26), were grown in the presence of a biologically relevant amount of exogenous PYO (33). Z-direction spatial mapping of the PYO redox ratio above the P. aeruginosa Δphz1/2 biofilm revealed a PYO electrocline, indicating that biosynthesis of PYO is not required for electrocline formation (Fig.…”

The Pseudomonas aeruginosa oxidative stress regulator OxyR influences production of pyocyanin and rhamnolipids: protective role of pyocyanin

“…Recently, pyocyanin was shown to have a function in signalling, responsible for the upregulation of specific genes, such as the genes involved in ferric iron acquisition and of the operon encoding the efflux pump MexGHI-OpmD PriceWhelan et al, 2006). Recently, it was shown that phenazine-defective mutants produce wrinkled colonies and accumulate NADH in the cells (Dietrich et al, 2008;Price-Whelan et al, 2007;Wangt & Newman, 2008). Pyocyanin is the phenazine that interacts most strongly with oxygen (Wangt & Newman, 2008) and it was proposed by Price-Whelan et al (2007) that externally added pyocyanin could give electrons to molecular oxygen to reduce it to water by oxidizing internal NADH to NAD.…”

“…Recently, it was shown that phenazine-defective mutants produce wrinkled colonies and accumulate NADH in the cells (Dietrich et al, 2008;Price-Whelan et al, 2007;Wangt & Newman, 2008). Pyocyanin is the phenazine that interacts most strongly with oxygen (Wangt & Newman, 2008) and it was proposed by Price-Whelan et al (2007) that externally added pyocyanin could give electrons to molecular oxygen to reduce it to water by oxidizing internal NADH to NAD. We indeed found that growth of the oxyR mutant in LB medium is restored in the presence of pyocyanin or phenazine 1-carboxylic acid.…”

Interspecies competition triggers virulence and mutability in Candida albicans–Pseudomonas aeruginosa mixed biofilms

“…of glucose consumption and affected the growth of C. albicans (Supplementary Figure S9). Price-whelan et al, (2007) demonstrated that pyocyanin alters the redox balance and the flow of carbon through the central metabolic routes in P. aeruginosa. These authors proposed that the superoxide radicals generated by pyocyanin can reduce the sulfhydro groups of the lipoamine cofactor from the E2 subunit of pyruvate dehydrogenase, resulting in inhibition of enzyme activity.…”