C. elegans discriminates colors to guide foraging.

Color detection is used by animals of diverse phyla to navigate colorful natural environments and is thought to require evolutionarily conserved opsin photoreceptor genes. We report that Caenorhabditis elegans roundworms can discriminate between colors despite the fact that they lack eyes and opsins. Specifically, we found that white light guides C. elegans foraging decisions away from a blue-pigment toxin secreted by harmful bacteria. These foraging decisions are guided by specific blue-to-amber ratios of light. The color specificity of color-dependent foraging varies notably among wild C. elegans strains, which indicates that color discrimination is ecologically important. We identified two evolutionarily conserved cellular stress response genes required for opsin-independent, color-dependent foraging by C. elegans, and we speculate that cellular stress response pathways can mediate spectral discrimination by photosensitive cells and organisms-even by those lacking opsins.

Evaluation of Pyocyanin induced systemic pathogenicity of Pseudomonas aeruginosa.

Pseudomonas aeruginosa (PA) is one of the most clinically significant nosocomial infectious agents. Clinical significance of this bacterium is intensified due to the phenomenon of its natural tendency for acquiring drug resistance mechanisms. PA produces pyocyanin (PCN), an important redox-active virulence factor. PCN has been detected in higher quantities in sputum samples of PA infected Cystic Fibrosis patients. PCN producing PA strains were isolated and characterized. Genomic 16s rRNA gene segment was amplified and sequenced (GenBank accession # jx280426). PCN was extracted and purified. In silico analysis yielded permeability and cytotoxic potential of PCN in modeled cell lines. PCN has high intestinal absorption, plasma protein binding potential, and permeability across biological membranes. Oral toxicity study in in silico rodent model classified PCN in class IV 'harmful if swallowed' (ld50 0.3-2g/kg). Cytotoxicity was assessed by oxidative stress levels in different organs in balb/c mice induced by intra peritoneal PCN injection. Significant alterations in oxidative stress levels in different organs of balb/c mice were observed. Increased levels of oxidative stress were observed in lungs, and heart, lower in liver and spleen while muscle tissues showed no significant difference in comparison to control.

Biofilm-forming ability and infection potential of Pseudomonas aeruginosa strains isolated from animals and humans.

Pseudomonas aeruginosa has been amongst the top 10 'superbugs' worldwide and is causing infections with poor outcomes in both humans and animals. From 202 P. aeruginosa isolates (n = 121 animal and n = 81 human), 40 were selected on the basis of biofilm-forming ability and were comparatively characterized in terms of virulence determinants to the type strain P. aeruginosa PAO1. Biofilm formation, pyocyanin and hemolysin production, and bacterial motility patterns were compared with the ability to kill human cell line A549 in vitro. On average, there was no significant difference between levels of animal and human cytotoxicity, while human isolates produced higher amounts of pyocyanin, hemolysins and showed increased swimming ability. Non-parametric statistical analysis identified the highest positive correlation between hemolysis and the swarming ability. For the first time an ensemble machine learning approach used on the in vitro virulence data determined the highest relative predictive importance of the submerged biofilm formation for the cytotoxicity, as an indicator of the infection ability. The findings from the in vitro study were validated in vivo using zebrafish (Danio rerio) embryos. This study highlighted no major differences between P. aeruginosa species isolated from animal and human infections and the importance of pyocyanin production in cytotoxicity and infection ability.

Pyocyanin induces systemic oxidative stress, inflammation and behavioral changes in vivo.

Pyocyanin (PCN) is a virulence factor secreted by Pseudomonas aeruginosa (P. aeruginosa) that has been shown to have numerous toxic effects in both in vitro and in vivo studies. Such toxicities include pro-inflammatory and pro-oxidant mediated responses. It is hypothesized that PCN can cross biological membranes and reach the systemic circulation, but no previous studies have investigated this. The aim of this study was, therefore, to quantify PCN in plasma and assess if systemic responses were occurring after localized intranasal administration in C57BL/6 J mice. This was achieved through the plasma quantification of PCN and assessment of changes to behavior using two commonly used tests, the forced swimming test and the open field test. Furthermore, evidence of systemic oxidative stress and inflammation was measured using malondialdehyde (MDA) and TNF-α post PCN exposure. PCN was found to cross into systemic circulation but in a variable manner. Furthermore, significant increases in plasma TNF-α and MDA (both p < 0.001) were observed along with changes in behavior indicative of systemic inflammatory responses.

Conjugate products of pyocyanin-glutathione reactions.

This "Letter to the Editor" is a "gentle but purposeful rejoinder" to specific comments made in pages 36-37 of your Muller and Merrett (2015) publication regarding the data presented in our Cheluvappa et al. (2008) paper. Our rebuttal topics include the effect of oxygen on the pyocyanin-glutathione reaction, relevance of reaction-duration to pathophysiology, rationale of experiments, veracity of statements germane to molecular-structure construction, and correction of hyperbole.

Mechanism for glutathione-mediated protection against the Pseudomonas aeruginosa redox toxin, pyocyanin.

Pseudomonas aeruginosa is an important human pathogen associated with several acute and chronic conditions, including diseases of the airways and wounds. The organism produces pyocyanin, an extracellular redox toxin that induces oxidative stress, depletes intracellular glutathione (GSH) and induces proliferative arrest and apoptosis, thus compromising the ability of tissue to repair itself. GSH is an important intra- and extracellular antioxidant, redox buffer and detoxifies xenobiotics by increasing their polarity, which facilitates their elimination. As previous studies have reported exogenous GSH to be protective against pyocyanin toxicity, this study was undertaken to explore the mechanism by which GSH protects host cells from the deleterious effects of the toxin. Co-incubation of pyocyanin with GSH resulted in a time-dependent diminished recovery of the toxin from the incubation medium. Concurrently, a highly polar green-colored metabolite was recovered that exhibited a UV-visible spectrum similar to pyocyanin and which was determined by mass spectrometry to have a major ion (m/z = 516) consistent with a glutathione conjugate. The ability of the conjugate to oxidize NADPH and to reduce molecular oxygen with the production of reactive oxygen species was comparable to pyocyanin yet it no longer demonstrated cytotoxicity towards host cells. These data suggest that GSH forms a cell-impermeant conjugate with pyocyanin and that availability of the thiol may be critical to minimizing the toxicity of this important bacterial virulence factor at infection sites. Our data indicate that for GSH to have a clinically effective role in neutralizing pyocyanin, the thiol needs to be available at millimolar concentrations.

Phenazine derivatives cause proteotoxicity and stress in C. elegans.

It is widely recognized that bacterial metabolites have toxic effects in animal systems. Phenazines are a common bacterial metabolite within the redox-active exotoxin class. These compounds have been shown to be toxic to the soil invertebrate Caenorhabditis elegans with the capability of causing oxidative stress and lethality. Here we report that chronic, low-level exposure to three separate phenazine molecules (phenazine-1-carboxylic acid, pyocyanin and 1-hydroxyphenazine) upregulated ER stress response and enhanced expression of a superoxide dismutase reporter in vivo. Exposure to these molecules also increased protein misfolding of polyglutamine and α-synuclein in the bodywall muscle cells of C. elegans. Exposure of worms to these phenazines caused additional sensitivity in dopamine neurons expressing wild-type α-synuclein, indicating a possible defect in protein homeostasis. The addition of an anti-oxidant failed to rescue the neurotoxic and protein aggregation phenotypes caused by these compounds. Thus, increased production of superoxide radicals that occurs in whole animals in response to these phenazines appears independent from the toxicity phenotype observed. Collectively, these data provide cause for further consideration of the neurodegenerative impact of phenazines.

Toxicity of imine-iminium dyes and pigments: electron transfer, radicals, oxidative stress and other physiological effects.

Although conjugation is well known as an important contributor to color, there is scant recognition concerning involvement of imine and iminium functions in the physiological effects of this class of dyes and pigments. The group includes the dyes methylene blue, rhodamine, malachite green, fuchsin, crystal violet, auramine and cyanins, in addition to the pigments consisting of pyocyanine, phthalocyanine and pheophytin. The physiological effects consist of both toxicity and beneficial aspects. The unifying theme of electron transfer-reactive oxygen species-oxidative stress is used as the rationale in both cases. Toxicity is frequently prevented or alleviated by antioxidants. The apparent dichotomy of methylene blue action as both oxidant and antioxidant is rationalized based on similar previous cases. This mechanistic approach may have practical benefit. This review is important in conveying, for the first time, a unifying mechanism for toxicity based on electron transfer-reactive oxygen species-oxidative stress arising from imine-iminium.

Unsuspected pyocyanin effect in yeast under anaerobiosis.

The blue-green phenazine, Pyocyanin (PYO), is a well-known virulence factor produced by Pseudomonas aeruginosa, notably during cystic fibrosis lung infections. It is toxic to both eukaryotic and bacterial cells and several mechanisms, including the induction of oxidative stress, have been postulated. However, the mechanism of PYO toxicity under the physiological conditions of oxygen limitation that are encountered by P. aeruginosa and by target organisms in vivo remains unclear. In this study, wild-type and mutant strains of the yeast Saccharomyces cerevisiae were used as an effective eukaryotic model to determine the toxicity of PYO (100-500 µmol/L) under key growth conditions. Under respiro-fermentative conditions (with glucose as substrate), WT strains and certain H2 O2 -hypersensitive strains showed a low-toxic response to PYO. Under respiratory conditions (with glycerol as substrate) all the strains tested were significantly more sensitive to PYO. Four antioxidants were tested but only N-acetylcysteine was capable of partially counteracting PYO toxicity. PYO did not appear to affect short-term respiratory O2 uptake, but it did seem to interfere with cyanide-poisoned mitochondria through a complex III-dependent mechanism. Therefore, a combination of oxidative stress and respiration disturbance could partly explain aerobic PYO toxicity. Surprisingly, the toxic effects of PYO were more significant under anaerobic conditions. More pronounced effects were observed in several strains including a 'petite' strain lacking mitochondrial DNA, strains with increased or decreased levels of ABC transporters, and strains deficient in DNA damage repair. Therefore, even though PYO is toxic for actively respiring cells, O2 may indirectly protect the cells from the higher anaerobic-linked toxicity of PYO. The increased sensitivity to PYO under anaerobic conditions is not unique to S. cerevisiae and was also observed in another yeast, Candida albicans.

Paradoxical role of 3-methyladenine in pyocyanin-induced toxicity in 1321N1 astrocytoma and SH-SY5Y neuroblastoma cells.

The role of autophagy in pyocyanin (PCN)-induced toxicity in the central nervous system (CNS) remains unclear, with only evidence from our group identifying it as a mechanism underlying toxicity in 1321N1 astrocytoma cells. Therefore, the aim of this study was to further examine the role of autophagy in PCN-induced toxicity in the CNS. To achieve this, we exposed 1321N1 astrocytoma and SH-SY5Y neuroblastoma cells to PCN (0-100 µmol/L) and tested the contribution of autophagy by measuring the impact of the autophagy inhibitor 3-methyladenine (3-MA) using a series of biochemical and molecular markers. Pretreatment of 1321N1 astrocytoma cells with 3-MA (5 mmol/L) decreased the PCN-induced acidic vesicular organelle and autophagosome formation as measured using acridine orange and green fluorescent protein-LC3 -LC3 fluorescence, respectively. Furthermore, 3-MA (5 mmol/L) significantly protected 1321N1 astrocytoma cells against PCN-induced toxicity. In contrast pretreatment with 3-MA (5 mmol/L) increased PCN-induced toxicity in SH-SY5Y neuroblastoma cells. Given the influence of autophagy in inflammatory responses, we investigated whether the observed effects in this study involved inflammatory mediators. The PCN (100 µmol/L) significantly increased the production of interleukin-8 (IL-8), prostaglandin E2 (PGE2), and leukotriene B4 (LTB4) in both cell lines. Consistent with its paradoxical role in modulating PCN-induced toxicity, 3-MA (5 mmol/L) significantly reduced the PCN-induced production of IL-8, PGE2, and LTB4 in 1321N1 astrocytoma cells but augmented their production in SH-SY5Y neuroblastoma cells. In conclusion, we show here for the first time the paradoxical role of autophagy in mediating PCN-induced toxicity in 1321N1 astrocytoma and SH-SY5Y neuroblastoma cells and provide novel evidence that these actions may be mediated by effects on IL-8, PGE2, and LTB4 production.

Identification of Pseudomonas aeruginosa phenazines that kill Caenorhabditis elegans.

Pathogenic microbes employ a variety of methods to overcome host defenses, including the production and dispersal of molecules that are toxic to their hosts. Pseudomonas aeruginosa, a Gram-negative bacterium, is a pathogen of a diverse variety of hosts including mammals and the nematode Caenorhabditis elegans. In this study, we identify three small molecules in the phenazine class that are produced by P. aeruginosa strain PA14 that are toxic to C. elegans. We demonstrate that 1-hydroxyphenazine, phenazine-1-carboxylic acid, and pyocyanin are capable of killing nematodes in a matter of hours. 1-hydroxyphenazine is toxic over a wide pH range, whereas the toxicities of phenazine-1-carboxylic acid and pyocyanin are pH-dependent at non-overlapping pH ranges. We found that acidification of the growth medium by PA14 activates the toxicity of phenazine-1-carboxylic acid, which is the primary toxic agent towards C. elegans in our assay. Pyocyanin is not toxic under acidic conditions and 1-hydroxyphenazine is produced at concentrations too low to kill C. elegans. These results suggest a role for phenazine-1-carboxylic acid in mammalian pathogenesis because PA14 mutants deficient in phenazine production have been shown to be defective in pathogenesis in mice. More generally, these data demonstrate how diversity within a class of metabolites could affect bacterial toxicity in different environmental niches.

Pseudomonas aeruginosa inhibits the growth of Cryptococcus species.

Pseudomonas aeruginosa is a ubiquitous and opportunistic bacterium that inhibits the growth of different microorganisms, including Gram-positive bacteria and fungi such as Candida spp. and Aspergillus fumigatus. In this study, we investigated the interaction between P. aeruginosa and Cryptococcus spp. We found that P. aeruginosa PA14 and, to a lesser extent, PAO1 significantly inhibited the growth of Cryptococcus spp. The inhibition of growth was observed on solid medium by the visualization of a zone of inhibition of yeast growth and in liquid culture by viable cell counting. Interestingly, such inhibition was only observed when P. aeruginosa and Cryptococcus were co-cultured. Minimal inhibition was observed when cell-cell contact was prevented using a separation membrane, suggesting that cell contact is required for inhibition. Using mutant strains of Pseudomonas quinoline signaling, we showed that P. aeruginosa inhibited the growth of Cryptococcus spp. by producing antifungal molecules pyocyanin, a redox-active phenazine, and 2-heptyl-3,4-dihydroxyquinoline (PQS), an extracellular quorum-sensing signal. Because both P. aeruginosa and Cryptococcus neoformans are commonly found in lung infections of immunocompromised patients, this study may have important implication for the interaction of these microbes in both an ecological and a clinical point of view.

Inhibition of autophagy by 3-methyladenine protects 1321N1 astrocytoma cells against pyocyanin- and 1-hydroxyphenazine-induced toxicity.

Central nervous system (CNS) infections due to Pseudomonas aeruginosa are difficult to treat and have a high mortality rate. Pyocyanin, a virulence factor produced by P. aeruginosa, has been shown to be responsible for the majority of P. aeruginosa's pathogenicity in mammalian cells. Several lines of evidence in respiratory cells suggest that this damage is primarily mediated by pyocyanin's ability to generate ROS and deplete host antioxidant defense mechanisms. However, it has yet to be established whether pyocyanin or 1-hydroxyphenazine have potential toxicity to the CNS. Therefore, the aim of this study was to compare the CNS toxicity of pyocyanin and 1-hydroxyphenazine in vitro and to provide insight into mechanisms that underlie this toxicity using 1321N1 astrocytoma cells. To achieve this, we investigated the contribution of oxidative stress and other mediators of cell death including autophagy, senescence and apoptosis. We show that oxidative stress is not a primary mediator of pyocyanin (0-100 µM) and 1-hydroxyphenazine (0-100 µM) induced toxicity in 1321N1 cells. Instead, our results suggest that autophagy may play a central role. The autophagy inhibitor 3-methyladenine (5 mM) protected 1321N1 astrocytoma cells against both pyocyanin and 1-hydroxyphenazine-induced cell injury and increased accumulation of acidic vesicular organelles, a hallmark of autophagy. Furthermore, apoptosis and senescence events may be secondary to autophagy in pyocyanin and 1-hydroxyphenazine-mediated cell injury. In conclusion, this study provides the first evidence on mechanisms underlying the toxicity of both pyocyanin and 1-hydroxyphenazine to astrocytoma cells and provides novel evidence suggesting that this toxicity may be mediated by the formation of acidic vesicular organelles, a hallmark of autophagic cell death.

Pyocyanin-induced toxicity in A549 respiratory cells is causally linked to oxidative stress.

Pyocyanin, a virulence factor produced by Pseudomonas aeruginosa, has many damaging effects on mammalian cells. Several lines of evidence suggest that this damage is primarily mediated by its ability to generate ROS and deplete host antioxidant defence mechanisms. However, a causal role for oxidative stress has not yet been demonstrated conclusively. Parallel measures of ROS production, antioxidant levels and cytotoxicity provide convincing evidence that pyocyanin-induced cytotoxicity in A549 respiratory cells is mediated by acute ROS production and subsequent oxidative stress. Pyocyanin increased ROS levels in A549 cells as measured by the fluorescent H(2)O(2) probes Amplex Red and DCFH-DA. These effects were attenuated by the antioxidant N-acetylcysteine. Furthermore, pyocyanin-induced depletion of intracellular GSH levels 24h after exposure was also prevented by pre-treatment of cells with NAC. Under these conditions, NAC protected cells against pyocyanin-induced cytotoxicity as measured by resazurin reduction to resorufin and viable cell counts, strongly supporting a causal role for oxidative stress. Finally, we also show that pyocyanin-induced activation of the immune and inflammatory transcription factor NF-κB in A549 cells is likely mediated by increased ROS. This increased understanding of mechanisms underlying pyocyanin-induced cytotoxicity may ultimately lead to better strategies for reducing the virulence associated with chronic P. aeruginosa infection.

Pseudomonas aeruginosa exotoxin pyocyanin causes cystic fibrosis airway pathogenesis.

The cystic fibrosis (CF) airway bacterial pathogen Pseudomonas aeruginosa secretes multiple virulence factors. Among these, the redox active exotoxin pyocyanin (PCN) is produced in concentrations up to 100 mumol/L during infection of CF and other bronchiectatic airways. However, the contributions of PCN during infection of bronchiectatic airways are not appreciated. In this study, we demonstrate that PCN is critical for chronic infection in mouse airways and orchestrates adaptive immune responses that mediate lung damage. Wild-type FVBN mice chronically exposed to PCN developed goblet cell hyperplasia and metaplasia, airway fibrosis, and alveolar airspace destruction. Furthermore, after 12 weeks of exposure to PCN, mouse lungs down-regulated the expression of T helper (Th) type 1 cytokines and polarized toward a Th2 response. Cellular analyses indicated that chronic exposure to PCN profoundly increased the lung population of recruited macrophages, CD4(+) T cells, and neutrophils responsible for the secretion of these cytokines. PCN-mediated goblet cell hyperplasia and metaplasia required Th2 cytokine signaling through the Stat6 pathway. In summary, this study establishes that PCN is an important P. aeruginosa virulence factor capable of directly inducing pulmonary pathophysiology in mice, consistent with changes observed in CF and other bronchiectasis lungs.

Small-colony variant selection as a survival strategy for Staphylococcus aureus in the presence of Pseudomonas aeruginosa.

Previously it has been demonstrated that Staphylococcus aureus is sensitive toward Pseudomonas-secreted exotoxins, which preferentially target the electron transport chain in staphylococci. Here it is shown that a subpopulation of S. aureus survives these respiratory toxins of Pseudomonas aeruginosa by selection of the small-colony variant (SCV) phenotype. Purified pyocyanin alone causes the same effect. A hemB mutant of S. aureus survives cocultivation with P. aeruginosa without a decrease in CFU.

Human targets of Pseudomonas aeruginosa pyocyanin.

Pseudomonas aeruginosa produces copious amounts of the redoxactive tricyclic compound pyocyanin that kills competing microbes and mammalian cells, especially during cystic fibrosis lung infection. Cross-phylum susceptibility to pyocyanin suggests the existence of evolutionarily conserved physiological targets. We screened a Saccharomyces cerevisiae deletion library to identify presumptive pyocyanin targets with the expectation that similar targets would be conserved in humans. Fifty S. cerevisiae targets were provisionally identified, of which 60% have orthologous human counterparts. These targets encompassed major cellular pathways involved in the cell cycle, electron transport and respiration, epidermal cell growth, protein sorting, vesicle transport, and the vacuolar ATPase. Using cultured human lung epithelial cells, we showed that pyocyanin-mediated reactive oxygen intermediates inactivate human vacuolar ATPase, supporting the validity of the yeast screen. We discuss how the inactivation of V-ATPase may negatively impact the lung function of cystic fibrosis patients.

The Pseudomonas aeruginosa secretory product pyocyanin inactivates alpha1 protease inhibitor: implications for the pathogenesis of cystic fibrosis lung disease.

Alpha1 Protease inhibitor (alpha1PI) modulates serine protease activity in the lung. Reactive oxygen species inactivate alpha1PI, and this process has been implicated in the pathogenesis of a variety of forms of lung injury. An imbalance of protease-antiprotease activity is also detected in the airways of patients with cystic fibrosis-associated lung disease who are infected with Pseudomonas aeruginosa. P. aeruginosa secretes pyocyanin, which, through its ability to redox cycle, induces cells to generate reactive oxygen species. We tested the hypothesis that redox cycling of pyocyanin could lead to inactivation of alpha1PI. When alpha1PI was exposed to NADH and pyocyanin, a combination that results in superoxide production, alpha1PI lost its ability to form an inhibitory complex with both porcine pancreatic elastase (PPE) and trypsin. Similarly, addition of pyocyanin to cultures of human airway epithelial cells to which alpha1PI was also added resulted in a loss of the ability of alpha1PI to form a complex with PPE or trypsin. Neither superoxide dismutase, catalase, nor dimethylthiourea nor depletion of the media of O2 to prevent formation of reactive oxygen species blocked pyocyanin-mediated inactivation of alpha1PI. These data raise the possibility that a direct interaction between reduced pyocyanin and alpha1PI is involved in the process. Consistent with this possibility, pretreatment of alpha1PI with the reducing agent beta-mercaptoethanol also inhibited binding of trypsin to alpha1PI. These data suggest that pyocyanin could contribute to lung injury in the P. aeruginosa-infected airway of cystic fibrosis patients by decreasing the ability of alpha1PI to control the local activity of serine proteases.