The Endogenous Stress Hormone CRH Modulates Excitatory Transmission and Network Physiology in Hippocampus

Memory is strongly influenced by stress but underlying mechanisms are unknown. Here, we used electrophysiology, neuroanatomy, and network simulations to probe the role of the endogenous, stress-related neuropeptide corticotropin-releasing hormone (CRH) in modulating hippocampal function. We focused on neuronal excitability and the incidence of sharp waves (SPWs), a form of intrinsic network activity associated with memory consolidation. Specifically, we blocked endogenous CRH using 2 chemically distinct antagonists of the principal hippocampal CRH receptor, CRHR1. The antagonists caused a modest reduction of spontaneous excitatory transmission onto CA3 pyramidal cells, mediated, in part by effects on I_AHP. This was accompanied by a decrease in the incidence but not amplitude of SPWs, indicating that the synaptic actions of CRH are sufficient to alter the output of a complex hippocampal network. A biophysical model of CA3 described how local actions of CRH produce macroscopic consequences including the observed changes in SPWs. Collectively, the results provide a first demonstration of the manner in which subtle synaptic effects of an endogenously released neuropeptide influence hippocampal network level operations and, in the case of CRH, may contribute to the effects of acute stress on memory.

Origin of the Force: The Force-From-Lipids Principle Applied to Piezo Channels

Piezo channels are a ubiquitously expressed, principal type of molecular force sensor in eukaryotes. They enable cells to decode a myriad of physical stimuli and are essential components of numerous mechanosensory processes. Central to their physiological role is the ability to change conformation in response to mechanical force. Here we discuss the evolutionary origin of Piezo in relation to other MS channels in addition to the force that gates Piezo channels. In particular, we discuss whether Piezo channels are inherently mechanosensitive in accordance with the force-from-lipid paradigm which has been firmly established for bacterial MS channels and two-pore domain K⁺ (K_2P) channels. We also discuss the evidence supporting a reliance on or direct interaction with structural scaffold proteins of the cytoskeleton and extracellular matrix according to the force-from-filament principle. In doing so, we explain the false dichotomy that these distinctions represent. We also discuss the possible unifying models that shed light on channel mechanosensitivity at the molecular level.

Enzymatic activity of albumin shown by coelenterazine chemiluminescence

Bioluminescence, the emission of light from live organisms, occurs in 18 phyla and is the major communication system in the deep sea. It has appeared independently many times during evolution but its origins remain unknown. Coelenterazine bioluminescence discovered in luminous jellyfish is the most common chemistry causing bioluminescence in the sea, occurring in seven phyla. Sequence similarities between coelenterazine luciferases and photoproteins from different phyla are poor (often < 5%). The aim of this study was to examine albumin that binds organic substances as a coelenterazine luciferase to test the hypothesis that the evolutionary origin of a bioluminescent protein was the result of the formation of a solvent cage containing just a few key amino acids. The results show for the first time that bovine and human albumin catalysed coelenterazine chemiluminescence consistent with a mono-oxygenase, whereas gelatin and haemoglobin, an oxygen carrier, had very weak activity. Insulin also catalysed coelenterazine chemiluminescence and was increased by Zn(2+). Albumin chemiluminescence was heat denaturable, exhibited saturable substrate characteristics and was inhibited by cations that bound these proteins and by drugs that bind to human albumin drug site I. Molecular modelling confirmed the coelenterazine binding site and identified four basic amino acids: lys195, arg222, his242 and arg257, potentially important in binding and catalysis similar to naturally occurring coelenterazine bioluminescent proteins. These results support the 'solvent cage' hypothesis for the evolutionary origin of enzymatic coelenterazine bioluminescent proteins. They also have important consequences in diseases such as diabetes, gut disorders and food intolerance where a mono-oxygenase could affect cell surface proteins.

Bacterial metabolic 'toxins': a new mechanism for lactose and food intolerance, and irritable bowel syndrome

Lactose and food intolerance cause a wide range of gut and systemic symptoms, including gas, gut pain, diarrhoea or constipation, severe headaches, severe fatigue, loss of cognitive functions such as concentration, memory and reasoning, muscle and joint pain, heart palpitations, and a variety of allergies (Matthews and Campbell, 2000; Matthews et al., 2005; Waud et al., 2008). These can be explained by the production of toxic metabolites from gut bacteria, as a result of anaerobic digestion of carbohydrates and other foods, not absorbed in the small intestine. These metabolites include alcohols, diols such as butan 2,3 diol, ketones, acids, and aldehydes such as methylglyoxal (Campbell et al., 2005, 2009). These 'toxins' induce calcium signals in bacteria and affect their growth, thereby acting to modify the balance of microflora in the gut (Campbell et al., 2004, 2007a,b). These bacterial 'toxins' also affect signalling mechanisms in cells around the body, thereby explaining the wide range of symptoms in people with food intolerance. This new mechanism also explains the most common referral to gastroenterologists, irritable bowel syndrome (IBS), and the illness that afflicted Charles Darwin for 50 years (Campbell and Matthews, 2005a,b). We propose it will lead to a new understanding of the molecular mechanism of type 2 diabetes and some cancers.

Distribution and regulation of stochasticity and plasticity in Saccharomyces cerevisiae

Stochasticity is an inherent feature of complex systems with nanoscale structure. In such systems information is represented by small collections of elements (e.g., a few electrons on a quantum dot), and small variations in the populations of these elements may lead to big uncertainties in the information. Unfortunately, little is known about how to work within this inherently noisy environment to design robust functionality into complex nanoscale systems. Here, we look to the biological cell as an intriguing model system where evolution has mediated the trade-offs between fluctuations and function, and in particular we look at the relationships and trade-offs between stochastic and deterministic responses in the gene expression of budding yeast (Saccharomyces cerevisiae). We find gene regulatory arrangements that control the stochastic and deterministic components of expression, and show that genes that have evolved to respond to stimuli (stress) in the most strongly deterministic way exhibit the most noise in the absence of the stimuli. We show that this relationship is consistent with a bursty two-state model of gene expression, and demonstrate that this regulatory motif generates the most uncertainty in gene expression when there is the greatest uncertainty in the optimal level of gene expression.

Gene network shaping of inherent noise spectra

Recent work demonstrates that stochastic fluctuations in molecular populations have consequences for gene regulation. Previous experiments focused on noise sources or noise propagation through gene networks by measuring noise magnitudes. However, in theoretical analysis, we showed that noise frequency content is determined by the underlying gene circuits, leading to a mapping between gene circuit structure and the noise frequency range. An intriguing prediction from our previous studies was that negative autoregulation shifts noise to higher frequencies where it is more easily filtered out by gene networks--a property that may contribute to the prevalence of autoregulation motifs (for example, found in the regulation of approximately 40% of Escherichia coli genes). Here we measure noise frequency content in growing cultures of E. coli, and verify the link between gene circuit structure and noise spectra by demonstrating the negative autoregulation-mediated spectral shift. We further demonstrate that noise spectral measurements provide mechanistic insights into gene regulation, as perturbations of gene circuit parameters are discernible in the measured noise frequency ranges. These results suggest that noise spectral measurements could facilitate the discovery of novel regulatory relationships.

Thrombolytic fibrin specificity influences activated partial thromboplastin time prolongation in vitro

Despite limited comparative data, guidelines suggest the same concomitant unfractionated heparin (UFH) dose for all fibrin-specific thrombolytic agents in acute myocardial infarction. Since a supratherapeutic activated partial thromboplastin time (aPTT) correlates with adverse outcomes, clarifying effects of various agents on aPTT are needed. The present in vitro study evaluated the influence of alteplase (rt-PA), reteplase (r-PA), and tenecteplase (TNK) on aPTT prolongation. Blood samples from healthy volunteers (n = 12) were treated with equipotent concentrations of rt-PA, r-PA, and TNK, with and without UFH. Samples of each treatment group were incubated at 37 degrees C; aPTT and fibrinogen activity were measured after 4 h. Mean aPTT values for rt-PA alone and r-PA alone were prolonged versus those of TNK alone (P = 0.001 for both). Combined with UFH, rt-PA and r-PA increased the aPTT versus UFH alone (P < 0.05 for both). Interestingly, TNK + UFH reduced the aPTT versus UFH alone (P < 0.001). A negative correlation existed between fibrinogen activity and aPTT for all treatments, except TNK alone. The present investigation illustrates that an agent with maximal fibrin specificity (TNK) has minimal effect on the aPTT, while agents with less fibrin specificity are more likely to prolong the aPTT, with and without UFH present.

A review of class III antiarrhythmic agents for atrial fibrillation: maintenance of normal sinus rhythm

A noteworthy shift from class I to class III antiarrhythmic agents for suppression of atrial fibrillation has occurred. Sotalol, amiodarone, and dofetilide have been evaluated for their ability to maintain sinus rhythm in patients with chronic atrial fibrillation. All of these agents are moderately effective; however, amiodarone appears to be most efficacious. Aside from their common class III actions, these agents have profoundly different pharmacologic, pharmacokinetic, safety, and drug interaction profiles that help guide drug selection. Amiodarone and dofetilide are safe in patients who have had a myocardial infarction and those with heart failure. The safety of commercially available d,l-sotalol in these patients is poorly understood. Torsades de pointes is the most serious adverse effect of sotalol and dofetilide, and risk increases with renal dysfunction. Amiodarone has minimal proarrhythmic risk but has numerous noncardiac toxicities that require frequent monitoring. Overall, an ideal antiarrhythmic agent does not exist, and drug selection should be highly individualized.

Assessment of structural features of the pseudomonas siderophore pyochelin required for its ability to promote oxidant-mediated endothelial cell injury

We previously showed that iron chelated to the Pseudomonas aeruginosa siderophore pyochelin enhances oxidant-mediated injury to pulmonary artery endothelial cells by catalyzing hydroxyl radical (HO(*)) formation. Therefore, we examined pyochelin structural/chemical features that may be important in this process. Five pyochelin analogues were examined for (i) capacity to accentuate oxidant-mediated endothelial cell injury, (ii) HO(*) catalytic ability, (iii) iron transfer to endothelial cells, and (iv) hydrophobicity. All compounds catalyzed similar HO(*) production, but only the hydrophobic ones containing a thiazolidine ring enhanced cell injury. Transfer of iron to endothelial cells did not correlate with cytotoxicity. Finally, binding of Fe(3+) by pyochelin led to Fe(2+) formation, perhaps explaining how Fe(3+)-pyochelin augments H(2)O(2)-mediated cell injury via HO(*) formation. The ability to bind iron in a catalytic form and the molecule's thiazolidine ring, which increases its hydrophobicity, are key to pyochelin's cytotoxicity. Reduction of Fe(3+) to Fe(2+) may also be important.

Porphyromonas endodontalis binds, reduces and grows on human hemoglobin

Porphyromonas endodontalis is a black-pigmented, obligate anaerobic rod-shaped bacterium implicated as playing a major role in endodontic infections. We have previously shown that P. endodontalis requires the porphyrin nucleus, preferably supplied as hemoglobin, as a growth supplement. The bacteria also actively transport free iron, although this activity does not support growth in the absence of a porphyrin source. The purpose of this study was to further investigate the binding and subsequent utilization of human hemoglobin by P. endodontalis. P. endodontalis binds hemoglobin and reduces the Fe(III) porphyrin, resulting in a steady accumulation of ferrous hemoglobin. Reduction of methemoglobin was similar to the extracellular reduction of nitrobluetetrazolium in the presence of oxidizable substrate. Turbidimetric and viable cell determinations showed that P. endodontalis grew when supplied only hemoglobin. Therefore, we conclude that hemoglobin appears to serve as a sole carbon and nitrogen source, and that these bacteria reduce extracellular compounds at the expense of oxidized substrates.

Growth stimulation of Porphyromonas endodontalis by hemoglobin and protoporphyrin IX

Porphyromonas endodontalis, like other Porphyromonas species, has a complex set of nutritional requirements. In addition to being an obligate anaerobe, the bacterium must be grown in a complex medium consisting of amino acids, reducing agents and heme compounds. P. endodontalis accumulates high concentrations of heme pigments to the extent that colonies appear black on blood agar. This accumulation of heme and the need for these compounds has been characterized as iron requirements by these species. However, in our studies, P. endodontalis demonstrated growth dependence on hemoglobin or protoporphyrin IX but not on free iron. Iron added to other heme compounds actually decreased growth stimulation by porphyrin-containing compounds. P. endodontalis actively transported free iron, but this process did not appear to be critical for growth. The maximum stimulation of growth by protoporphyrin IX, under conditions of iron deprivation, suggests that P. endodontalis requires the porphyrin moiety as a growth factor.

The measurement of toluene dioxygenase activity in biofilm culture of Pseudomonas putida F1

Toluene dioxygenase (Tod) enzyme activity can be measured by the conversion of indole to indigo. Indigo is measured spectrophotometrically at 600 nm. However, this method is inadequate to measure the whole-cell enzyme activity when interference by suspended biomass is present. Indoxyl is a highly fluorescent intermediate in the conversion of indole to indigo by Tod. A fluorescence-based assay was developed and applied to monitor Tod activity in whole cells of Pseudomonas putida F1 biofilm from a continuously operated biofilter. Suspended growth studies with pure cultures indicated that indoxyl, as measured by fluorescence, correlated with indigo production (r(2)=0.89) as measured by spectrophotometry. Whole-cell enzyme activity was followed during growth on a minimal medium containing toluene. The maximum normalized whole cell enzyme activity of 19+/-1.5x10(-4) mg indigo (mg protein)(-1) min(-1) was reached during early stationary phase. P. putida F1 cells from a biofilm grown on vapor phase toluene had a normalized whole-cell enzyme activity of 5.0+/-0.2x10(-4) mg indigo (mg protein)(-1) min(-1). The half-life of whole-cell enzyme activity was estimated to be between 5.5 and 8 h in both suspended and biofilm growth conditions.

Iron acquisition from Pseudomonas aeruginosa siderophores by human phagocytes: an additional mechanism of host defense through iron sequestration?

Chelation of iron to iron-binding proteins is a strategy of host defense. Some pathogens counter this via the secretion of low-molecular-weight iron-chelating agents (siderophores). Human phagocytes possess a high-capacity mechanism for iron acquisition from low-molecular-weight iron chelates. Efficient acquisition and sequestration of iron bound to bacterial siderophores by host phagocytes could provide a secondary mechanism to limit microbial access to iron. In the present work we report that human neutrophils, macrophages, and myeloid cell lines can acquire iron from the two Pseudomonas aeruginosa siderophores. Analogous to iron acquisition from other low-molecular-weight chelates, iron acquisition from the siderophores is ATP independent, induced by multivalent cationic metals, and unaffected by inhibitors of endocytosis and pinocytosis. In vivo, this process could serve as an additional mechanism of host defense to limit iron availability to invading siderophore-producing microbes.

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.

Pseudomonas pyocyanin increases interleukin-8 expression by human airway epithelial cells

Pseudomonas aeruginosa, an opportunistic human pathogen, causes acute pneumonia in patients with hospital-acquired infections and is commonly associated with chronic lung disease in individuals with cystic fibrosis (CF). Evidence suggests that the pathophysiological effects of P. aeruginosa are mediated in part by virulence factors secreted by the bacterium. Among these factors is pyocyanin, a redox active compound that increases intracellular oxidant stress. We find that pyocyanin increases release of interleukin-8 (IL-8) by both normal and CF airway epithelial cell lines and by primary airway epithelial cells. Moreover, pyocyanin synergizes with the inflammatory cytokines tumor necrosis factor alpha and IL-1alpha. RNase protection assays indicate that increased IL-8 release is accompanied by increased levels of IL-8 mRNA. The antioxidant n-acetyl cysteine, general inhibitors of protein tyrosine kinases, and specific inhibitors of mitogen-activated protein kinases diminish pyocyanin-dependent increases in IL-8 release. Conversely, inhibitors of protein kinases C (PKC) and PKA have no effect. In contrast to its effects on IL-8 expression, pyocyanin inhibits cytokine-dependent expression of the monocyte/macrophage/T-cell chemokine RANTES. Increased release of IL-8, a potent neutrophil chemoattractant, in response to pyocyanin could contribute to the marked infiltration of neutrophils and subsequent neutrophil-mediated tissue damage that are observed in Pseudomonas-associated lung disease.

Copper-binding compounds from Methylosinus trichosporium OB3b

Two copper-binding compounds/cofactors (CBCs) were isolated from the spent media of both the wild type and a constitutive soluble methane monooxygenase (sMMOC) mutant, PP319 (P. A. Phelps et al., Appl. Environ. Microbiol. 58:3701-3708, 1992), of Methylosinus trichosporium OB3b. Both CBCs are small polypeptides with molecular masses of 1,218 and 779 Da for CBC-L1 and CBC-L2, respectively. The amino acid sequence of CBC-L1 is S?MYPGS?M, and that of CBC-L2 is SPMP?S. Copper-free CBCs showed absorption maxima at 204, 275, 333, and 356 with shoulders at 222 and 400 nm. Copper-containing CBCs showed a broad absorption maximum at 245 nm. The low-temperature electron paramagnetic resonance (EPR) spectra of copper-containing CBC-L1 showed the presence of a copper center with an EPR splitting constant between those of type 1 and type 2 copper centers (g = 2.087, g = 2.42 G, A = 128 G). The EPR spectrum of CBC-L2 was more complex and showed two spectrally distinct copper centers. One signal can be attributed to a type 2 Cu2+ center (g = 2.073, g = 2.324 G, A = 144 G) which could be saturated at higher powers, while the second shows a broad, nearly isotropic signal near g = 2.063. In wild-type strains, the concentrations of CBCs in the spent media were highest in cells expressing the pMMO and stressed for copper. In contrast to wild-type strains, high concentrations of CBCs were observed in the extracellular fraction of the sMMOC mutants PP319 and PP359 regardless of the copper concentration in the culture medium.

Pseudomonas pyocyanine alters calcium signaling in human airway epithelial cells

Pseudomonas aeruginosa, an opportunistic human pathogen, causes both acute and chronic lung disease. P. aeruginosa exerts many of its pathophysiological effects by secreting virulence factors, including pyocyanine, a redox-active compound that increases intracellular oxidant stress. Because oxidant stress has been shown to affect cytosolic Ca2+ concentration ([Ca2+]c) in other cell types, we studied the effect of pyocyanine on [Ca2+]c in human airway epithelial cells (A549 and HBE). At lower concentrations, pyocyanine inhibits inositol 1,4,5-trisphosphate formation and [Ca2+]c increases in response to G protein-coupled receptor agonists. Conversely, at higher concentrations, pyocyanine itself increases [Ca2+]c. The pyocyanine-dependent [Ca2+]c increase appears to be oxidant dependent and to result from increased inositol trisphosphate and release of Ca2+ from intracellular stores. Ca2+ plays a central role in epithelial cell function, including regulation of ion transport, mucus secretion, and ciliary beat frequency. By disrupting Ca2+ homeostasis, pyocyanine could interfere with these critical functions and contribute to the pathophysiological effects observed in Pseudomonas-associated lung disease.

Effect of red blood cells on the growth of Porphyromonas endodontalis and microbial community development

Establishment of a microbial community in the root canal system depends on numerous factors, of which nutrient availability may be one of the most important. We hypothesized that the presence of red blood cells or hemoglobin in this environment could cause shifts in microbial composition of communities, resulting in organisms such as Porphyromonas endodontalis becoming more dominant. An in vitro model system using mixed, batch cultures was performed with the bacteria P. endodontalis, Fusobacterium nucleatum, Peptostreptococcus micros and Campylobacter rectus. Bacteria were cultured in media with or without the addition of washed red blood cells, hemoglobin, or serum. Cyclic growth studies revealed that P. endodontalis was lost from the community of organisms after three cycles. However, inclusion of red blood cells resulted in establishment of this organism. Moreover, red blood cells added to pure cultures of P. endodontalis substantially enhanced growth and protected the organisms from oxygen. We conclude that the presence of red blood cells could result in shifts of microbial communities of organisms within the root canal system.

Binding of iron and inhibition of iron-dependent oxidative cell injury by the "calcium chelator" 1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid (BAPTA)

A role for increases in intracellular calcium (Ca2+) has been suggested in the pathophysiology of various forms of oxidant-mediated cell injury. In recent studies, we found that iron bound to the Pseudomonas aeruginosa siderophore, pyochelin, augments oxidant-mediated endothelial cell injury by catalyzing the formation of hydroxyl radical (HO.). To investigate the role of Ca2+ in this process, the effects of two Ca2+ chelating agents, Fura-2 and 1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid (BAPTA), were assessed. BAPTA, but not Fura-2, was protective against H2O2/ferripyochelin-mediated injury. Subsequent data suggested that chelation of iron rather than Ca2+ by BAPTA was most likely responsible. Spectrophotometry demonstrated that both ferrous (Fe2+) and ferric (Fe3+) iron formed a complex with BAPTA. The affinity of BAPTA for the metals was Fe3+ > Ca2+ > Fe2+. BAPTA was found to decrease markedly iron-catalyzed production of HO. and/or ferryl species when analyzed by spin trapping. Although our results do not definitively prove that BAPTA protects endothelial cells from ferripyochelin-associated damage by chelating iron, these data indicate that caution must be exercised in utilizing protective effects of intracellular "Ca2+ chelating agents" as evidence for a role of alterations in cellular Ca2+ levels in experimental conditions in which iron-mediated oxidant production is also occurring.

Augmentation of oxidant injury to human pulmonary epithelial cells by the Pseudomonas aeruginosa siderophore pyochelin

Pseudomonas aeruginosa causes acute and chronic infections of the human lung, with resultant tissue injury. We have previously shown that iron bound to pyochelin, a siderophore secreted by the organism to acquire iron, is an efficient catalyst for hydroxyl radical (HO.) formation and augments injury to pulmonary artery endothelial cells resulting from their exposure to superoxide (O2.) and/or H2O2. Sources for O2-. and H2O2 included phorbol myristate acetate (PMA)-stimulated neutrophils and pyocyanin. Pyocyanin, another P. aeruginosa secretory product, undergoes cell-mediated redox, thereby forming O2-. and H2O2. In P. aeruginosa lung infections, damage to airway epithelial cells is probably more extensive than that to endothelial cells. Therefore, we examined whether ferripyochelin also augments oxidant-mediated damage to airway epithelial cells. A549 cells, a human type II alveolar epithelial cell line, was exposed to H2O2, PMA-stimulated neutrophils, or pyocyanin, and injury was determined by release of 51Cr from prelabeled cells. Ferripyochelin significantly increased (> 10-fold) oxidant-mediated cell injury regardless of whether H2O2, neutrophils, or pyocyanin was employed. Apo-pyochelin was not effective, and ferripyochelin was not toxic by itself at the concentrations employed. Spin trapping with alpha-(4-pyrridyl-1-oxide)-N-t-butyl-nitrone-ethanol confirmed the generation of HO., and injury was decreased by a variety of antioxidants, including superoxide dismutase, catalase, and dimethylthiourea. These data are consistent with the hypothesis that the presence of ferripyochelin at sites of P. aeruginosa lung infection could contribute to tissue injury through its ability to promote HO.-mediated damage to airway epithelial cells.

Ferric uptake regulator mutants of Pseudomonas aeruginosa with distinct alterations in the iron-dependent repression of exotoxin A and siderophores in aerobic and microaerobic environments

Because the ferric uptake regulator (fur) appears to be an essential gene in Pseudomonas aeruginosa, resistance to manganese was used as an enrichment to isolate strains carrying point mutations in the fur gene in order to assess its role in the co-ordinate expression of siderophores and exotoxin A (ETA). This report describes a detailed molecular and phenotypic characterization of four mutants and one revertant, which carry point mutations in the fur gene. Two parental strains were used in this study. Three mutants were isolated from the widely used strain, PAO1. One of these, CS (cold sensitive), has a mutation in the 5' non-coding region of the fur gene while the two other mutants derived from this parent have mutations resulting in the following deduced changes in Fur: mutant A2, H86-->R; mutant A4, H86-->Y. The other mutant (C6) and its revertant (C6Rv) were derived from PAO6261, a mutant of PAO1 with a deletion in the anr gene (anaerobic regulation of arginine deiminase and nitrate reduction) that controls anaerobic respiration in P. aeruginosa. Fur from the C6 mutant has an A10-->G mutation while in the C6Rv spontaneous revertant the mutant Gly residue has been changed to Ser at this position. All mutants were examined for alterations in the iron-regulated expression of siderophores and ETA. The A2 and A4 mutants expressed higher levels of siderophores in iron-deficient media and in iron-replete media. The CS mutant constitutively expressed siderophores at 25 degrees C. At 42 degrees C siderophore biosynthesis was iron repressed as in the parental strain PAO1. The deletion of anr in PAO6261 had no apparent effect on the iron-mediated regulation of siderophore synthesis, but the C6 mutant derived from this strain produces siderophores constitutively. The iron-regulated production of siderophores by C6Rv was similar to the parental strain PAO6261 and PAO1. Because one of the parental strains used in this study is an Anr mutant, regulation of ETA production was assessed under aerobic and microaerobic conditions. Iron-dependent repression of ETA synthesis in both parental strains and A2 and A4 mutants was found to be 50-100-fold under aerobic and microaerobic conditions, as assayed by quantitative Western dot-blot assays. By contrast in the CS and C6 mutants, while iron-dependent repression os ETA synthesis was similar to both parental strains under aerobic conditions, ETA production in these mutants was constitutive in a microaerobic environment. RNase protection analysis of toxA and regAB transcription in PAO1, PAO6261 and the C6 mutant corroborated the results of quantitative dot-blot assays of ETA. The mutant Fur proteins were purified and examined for their ability to bind to the promoter of a gene (pvdS) that positively regulates the expression of siderophores and ETA. Fur from the A2 and A4 mutants and from the C6Rv revertant was able to bind to the target DNA, but with reduced affinity by comparison to wild-type Fur. Fur from the C6 mutant in DNase I footprint experiments failed to protect the promoter region of the pvdS gene, but it retained some weak binding activity in gel mobility shift assays. The data presented in this study not only furnish some additional insights into the structure-function relationships of Fur, but also afford novel perspectives of virulence factors in P. aeruginosa under environmental conditions that have not previously been considered.

Protease cleavage of iron-transferrin augments pyocyanin-mediated endothelial cell injury via promotion of hydroxyl radical formation

Although a number of bacterium- and host-derived factors have been suggested to contribute to the pathogenesis of Pseudomonas aeruginosa-associated tissue injury, the mechanism remains unclear. We have previously shown that protease modification of iron (Fe)-transferrin generates new iron chelates capable of catalyzing hydroxyl radical (.OH) formation from superoxide and hydrogen peroxide. The latter two oxidants are generated during redox cycling of another P. aeruginosa secretory product, pyocyanin. The lung is a major site of P. aeruginosa infection, with damage to local endothelial cells contributing to the pathogenesis of such infections. Endothelial cells are highly susceptible to oxidant-mediated injury. Therefore, we examined whether pseudomonas elastase-cleaved Fe-transferrin and pyocyanin synergistically enhance pulmonary artery endothelial cell injury via .OH formation. By measuring 51Cr release from cultured endothelial cell monolayers, pseudomonas elastase-cleaved Fe-transferrin significantly augmented cell injury resulting from cellular exposure to sublethal concentrations of pyocyanin. This enhancement in injury was not protease specific, as similar results were obtained with pyocyanin in combination with trypsin- or porcine pancreatic elastase-cleaved Fe-transferrin. The association of iron with the transferrin appeared to be necessary in this process. Supporting the involvement of .OH generation via the Haber-Weiss reaction in augmenting cell injury, catalase, dimethyl thiourea, superoxide dismutase, deferoxamine, and dimethyl sulfoxide significantly inhibited cell injury resulting from exposure to pyocyanin and protease-cleaved Fe-transferrin. Furthermore, spin trapping demonstrated the production of .OH in this cellular system. We conclude that .OH formation resulting from the interaction of protease-cleaved Fe-transferrin and endothelial cell redox cycling of pyocyanin may contribute to P. aeruginosa-associated tissue injury via endothelial cell injury.

Pyocyanin from Pseudomonas aeruginosa inhibits prostacyclin release from endothelial cells

Pseudomonas aeruginosa pneumonia causes a vasculitis of small pulmonary arteries. While the fully developed lesion demonstrates vessel wall necrosis, the early lesion is remarkable for preservation of viable endothelium despite vessel wall invasion by bacteria. Pyocyanin, an exoproduct of P. aeruginosa, markedly inhibited prostacyclin production by pulmonary artery endothelial cells without causing cell lysis. Pyocyanin might after vascular homeostasis in the absence of cytolysis.

Pseudomonas siderophore pyochelin enhances neutrophil-mediated endothelial cell injury

Pyochelin, a siderophore secreted by Pseudomonas aeruginosa, binds iron in a form which can catalyze the formation of hydroxyl radical (.OH) from neutrophil-derived superoxide (O2-.) and hydrogen peroxide (H2O2). Ferripyochelin induced a concentration-dependent increase in endothelial cell injury (51Cr release) resulting from exposure to H2O2, a xanthine/xanthine oxidase O2-./H2O2 generating system, or stimulated neutrophils. This process was dependent on the presence of iron. Formation of .OH was confirmed using spin trapping. Although a slight (13%) increase in neutrophil O2-. production in the presence of ferripyochelin was observed, this did not appear to account for the extent of endothelial cell injury observed. The antioxidants dimethylthiourea and catalase decreased endothelial cell injury, whereas dimethyl sulfoxide and superoxide dismutase were without effect. Fe-nitrilotriacetic acid and Fe-EDTA, which are also .OH catalysts, did not augment endothelial cell injury resulting from exposure to the above oxidant systems. In contrast to results with the endothelial cells, killing of P. aeruginosa by O2-./H2O2 derived from the reaction of xanthine and xanthine oxidase was not increased by ferripyochelin. These data are consistent with the possibility that the interaction of Pseudomonas- and phagocyte-derived secretory products could contribute to local tissue injury at sites of P. aeruginosa infection by causing the generation of .OH.

Coordinate regulation of siderophore and exotoxin A production: molecular cloning and sequencing of the Pseudomonas aeruginosa fur gene

A 5.9-kb DNA fragment was cloned from Pseudomonas aeruginosa PA103 by its ability to functionally complement a fur mutation in Escherichia coli. A fur null mutant E. coli strain that contains multiple copies of the 5.9-kb DNA fragment produces a 15-kDa protein which cross-reacts with a polyclonal anti-E. coli Fur serum. Sequencing of a subclone of the 5.9-kb DNA fragment identified an open reading frame predicted to encode a protein 53% identical to E. coli Fur and 49% identical to Vibrio cholerae Fur and Yersinia pestis Fur. While there is extensive homology among these Fur proteins, Fur from P. aeruginosa differs markedly at its carboxy terminus from all of the other Fur proteins. It has been proposed that this region is a metal-binding domain in E. coli Fur. A positive selection procedure involving the isolation of manganese-resistant mutants was used to isolate mutants of strain PA103 that produce altered Fur proteins. These manganese-resistant Fur mutants constitutively produce siderophores and exotoxin A when grown in concentrations of iron that normally repress their production. A multicopy plasmid carrying the P. aeruginosa fur gene restores manganese susceptibility and wild-type regulation of exotoxin A and siderophore production in these Fur mutants.

Interaction of the Pseudomonas aeruginosa secretory products pyocyanin and pyochelin generates hydroxyl radical and causes synergistic damage to endothelial cells. Implications for Pseudomonas-associated tissue injury

Pyocyanin, a secretory product of Pseudomonas aeruginosa, has the capacity to undergo redox cycling under aerobic conditions with resulting generation of superoxide and hydrogen peroxide. By using spin trapping techniques in conjunction with electron paramagnetic resonance spectrometry (EPR), superoxide was detected during the aerobic reduction of pyocyanin by NADH or porcine endothelial cells. No evidence of hydroxyl radical formation was detected. Chromium oxalate eliminated the EPR spectrum of the superoxide-derived spin adduct resulting from endothelial cell exposure to pyocyanin, suggesting superoxide formation close to the endothelial cell plasma membrane. We have previously reported that iron bound to the P. aeruginosa siderophore pyochelin (ferripyochelin) catalyzes the formation of hydroxyl free radical from superoxide and hydrogen peroxide via the Haber-Weiss reaction. In the present study, spin trap evidence of hydroxyl radical formation was detected when NADH and pyocyanin were allowed to react in the presence of ferripyochelin. Similarly, endothelial cell exposure to pyocyanin and ferripyochelin also resulted in hydroxyl radical production which appeared to occur in close proximity to the cell surface. As assessed by 51Cr release, endothelial cells which were treated with pyocyanin or ferripyochelin alone demonstrated minimal injury. However, endothelial cell exposure to the combination of pyochelin and pyocyanin resulted in 55% specific 51Cr release. Injury was not observed with the substitution of iron-free pyochelin and was diminished by the presence of catalase or dimethyl thiourea. These data suggest the possibility that the P. aeruginosa secretory products pyocyanin and pyochelin may act synergistically via the generation of hydroxyl radical to damage local tissues at sites of pseudomonas infection.

Mutasynthesis of siderophore analogues by Pseudomonas aeruginosa

The Gram-negative bacterium Pseudomonas aeruginosa produces the phenolic siderophore pyochelin. Salicylic acid is an intermediate in the pyochelin biosynthetic pathway, and mutants blocked in salicylic acid biosynthesis (Sal-) are able to incorporate exogenously supplied salicylic acid into pyochelin. A P. aeruginosa Sal- mutant was incubated with 13 salicylic acid analogues and was found to incorporate three (5-fluorosalicylic acid, 4-methylsalicylic acid, and 3-hydroxypicolinic acid) into pyochelin analogues, trivially designated as 5-fluoropyochelin, 4-methylpyochelin, and 6-azapyochelin. The structures of the mutasynthetic products were confirmed by 1H and 13C NMR and high-resolution fast atom bombardment mass spectrometry as being identical to pyochelin except for the expected changes in the aromatic ring. The biological activity of the three pyochelin analogues was determined in iron transport assays. In comparison to pyochelin, 4-methylpyochelin was more active in the assays whereas the activities of 5-fluoropyochelin and 6-azapyochelin were markedly decreased. In coincubation assays, 5-fluoropyochelin substantially inhibited iron transport by pyochelin; 4-methylpyochelin and 6-azapyochelin did not demonstrate this inhibitory effect.

Possible role of bacterial siderophores in inflammation. Iron bound to the Pseudomonas siderophore pyochelin can function as a hydroxyl radical catalyst

Tissue injury has been linked to neutrophil associated hydroxyl radical (.OH) generation, a process that requires an exogenous transition metal catalyst such as iron. In vivo most iron is bound in a noncatalytic form. To obtain iron required for growth, many bacteria secrete iron chelators (siderophores). Since Pseudomonas aeruginosa infections are associated with considerable tissue destruction, we examined whether iron bound to the Pseudomonas siderophores pyochelin (PCH) and pyoverdin (PVD) could act as .OH catalysts. Purified PCH and PVD were iron loaded (Fe-PCH, Fe-PVD) and added to a hypoxanthine/xanthine oxidase superoxide- (.O2-) and hydrogen peroxide (H2O2)-generating system. Evidence for .OH generation was then sought using two different spin-trapping agents (5.5 dimethyl-pyrroline-1-oxide or N-t-butyl-alpha-phenylnitrone), as well as the deoxyribose oxidation assay. Regardless of methodology, .OH generation was detected in the presence of Fe-PCH but not Fe-PVD. Inhibition of the process by catalase and/or SOD suggested .OH formation with Fe-PCH occurred via the Haber-Weiss reaction. Similar results were obtained when stimulated neutrophils were used as the source of .O2- and H2O2. Addition of Fe-PCH but not Fe-PVD to stimulated neutrophils yielded .OH as detected by the above assay systems. Since PCH and PVD bind ferric (Fe3+) but not ferrous (Fe2+) iron, .OH catalysis with Fe-PCH would likely involve .O2(-)-mediated reduction of Fe3+ to Fe2+ with subsequent release of "free" Fe2+. This was confirmed by measuring formation of the Fe2(+)-ferrozine complex after exposure of Fe-PCH, but not Fe-PVD, to enzymatically generated .O2-. These data show that Fe-PCH, but not Fe-PVD, is capable of catalyzing generation of .OH. Such a process could represent as yet another mechanism of tissue injury at sites of infection with P. aeruginosa.

Isolation and characterization of Pseudomonas aeruginosa mutants requiring salicylic acid for pyochelin biosynthesis

Pseudomonas aeruginosa mutants requiring salicylic acid for pyochelin biosynthesis were isolated after chemical mutagenesis by plating on a siderophore detection medium. Like the wild type, these mutants incorporated 7-[14C]salicylic acid into pyochelin, demonstrating that salicylic acid is an intermediate in the biosynthesis pathway of pyochelin.

Synthesis and biological activity of pyochelin, a siderophore of Pseudomonas aeruginosa

Pyochelin, a phenolic siderophore of Pseudomonas aeruginosa, was synthesized in three steps from salicylonitrile, L-cysteine, and L-N-methylcysteine. The synthetic product was determined to be identical to natural pyochelin by 1H nuclear magnetic resonance spectroscopy, fast atom bombardment mass spectrometry, chromatographic analysis, and chemical reactivity with FeCl3 and ammoniacal silver nitrate reagent. Synthetic and natural pyochelin promoted bacterial growth in iron-depleted medium and were also found to mediate iron transport by P. aeruginosa to the same levels. Neopyochelin, a stereoisomeric by-product of the synthesis, showed less biological activity than did pyochelin in iron transport assays.

Mapping of mutations in Pseudomonas aeruginosa defective in pyoverdin production

Twelve mutants of Pseudomonas aeruginosa PAO defective in pyoverdin production were isolated (after chemical and transposon mutagenesis) that were nonfluorescent and unable to grow on medium containing 400 microM ethylenediaminedi(o-hydroxyphenylacetic acid). Four mutants were unable to produce hydroxamate, six were hydroxamate positive, one was temperature sensitive for pyoverdin production, and another was unable to synthesize pyoverdin on succinate minimal medium but was capable of synthesizing pyoverdin when grown on Casamino Acids medium (Difco Laboratories, Detroit, Mich.). The mutations were mapped on the PAO chromosome. All the mutations affecting pyoverdin production were located at 65 to 70 min, between catA1 and mtu-9002.

Siderophore-mediated iron acquisition from transferrin by Pseudomonas aeruginosa

Pseudomonas aeruginosa placed across a dialysis membrane from [55Fe]transferrin caused the mobilization of the iron from the transferrin side to the bacterial or dialysate side of the membrane. Although the bacteria were capable of obtaining iron from transferrin for growth, the siderophores of P. aeruginosa failed to convert iron bound to transferrin into dialyzable, low-molecular-weight chelates. The crucial factor produced by the bacteria which was not present when the siderophores were added alone was the acid produced from the glucose minimal medium. The siderophores mobilized considerable iron from transferrin when used in the dialysis assay at pH values between 5.0 and 6.0, values which were commonly found during incubation of bacteria in the assays. When the siderophores were tested individually, pyoverdin was more effective than pyochelin in mobilizing iron across dialysis membranes at pH values of 5.0 and 6.0, but neither had appreciable activity at pH 7.4. The amounts of iron mobilized from conalbumin were comparable to the amounts from transferrin, but there was negligible release from lactoferrin at the three pH values. When the two siderophores were combined, the level of iron mobilization was identical to that demonstrated by pyoverdin alone. When the dialysis membrane was removed and the bacteria were mixed with the siderophores and transferrin, pyoverdin was again more active than pyochelin in mediating iron transport. Although no pyochelin-mediated iron mobilization could be detected at pH 7.4, there was transport. Therefore, the bacteria appeared to be aiding the siderophores in iron mobilization from transferrin.

Role of pyocyanin in the acquisition of iron from transferrin

Pseudomonas aeruginosa produces a blue pigment called pyocyanin. In the presence of oxidizable substrates, bacteria reduce this pigment to a colorless product, leukopyocyanin. Pyocyanin can also be nonenzymatically reduced by NADH. Leukopyocyanin formed by cell- or NADH-mediated reduction nonenzymatically reduces oxygen or Fe(III). Pyocyanin-dependent iron reduction by whole bacterial cells was measured by the formation of the ferrous-ferrozine complex. In addition, leukopyocyanin reduced chelated Fe(III) including ferric iron in complex with transferrin, the serum iron-binding protein. High-pressure liquid chromatography was used to display the reductive removal of iron from transferrin and the accumulation of iron in the ferrous-ferrozine complex. Pyocyanin stimulated the accumulation of 55Fe from [55Fe]transferrin when it was added to bacteria incubated under low-oxygen conditions. Although bacteria grown in the presence of 100 microM FeCl3 reduced pyocyanin just as rapidly as iron-limited bacteria, these cells did not accumulate iron in the presence or absence of pyocyanin. Therefore, P. aeruginosa participates indiscriminantly in the reduction of pyocyanin, but soluble or available iron generated by the pyocyanin is taken up specifically by iron-limited bacteria.

Effects of siderophores on the growth of Pseudomonas aeruginosa in human serum and transferrin

A combination of the siderophores produced by Pseudomonas aeruginosa, pyochelin and pyoverdin, dramatically stimulates the growth of this bacterium in medium containing human transferrin. The amount of growth stimulation observed when each siderophore was added alone was only slightly less than the amount observed with the combination. Siderophore-defective mutants of strain PAO1 were isolated to test the effects of siderophore production on growth in transferrin and human serum. The pyoverdin-proficient (Pvd+), pyochelin-deficient (Pch-) strain (IA5) grows just as well as the parent (PAO1), which produces both siderophores. On the other hand, the Pvd- Pch+ strain (211-5) has severely retarded growth, similar to that demonstrated by a mutant lacking production of both siderophores (IA1), but has an accelerated log phase compared with strain IA1 at the later stages of the growth curve. However, the Pvd- Pch+ strain (211-5) had no observable advantage over the Pvd- Pch- strain, IA1, during incubation in human serum. The inability of P. aeruginosa strains to produce pyochelin in glucose-minimal medium may explain the poor growth of 211-5 in this medium and in human serum. The 211-5 strain grows much better than the IA1 strain in the medium that allows pyochelin synthesis, but it still does not grow as well as the Pvd+ Pch- strain (IA5). Therefore, pyoverdin appears to be the most important siderophore for growth in human serum.

Genetic mapping and characterization of Pseudomonas aeruginosa mutants that hyperproduce exoproteins

We isolated two mutants of Pseudomonas aeruginosa PAO with defective iron uptake. In contrast to the wild-type strain, the mutants produced extracellular protease activity in media containing high concentrations of salts or iron and hyperproduced elastase, staphylolytic enzyme, and exotoxin A in ordinary media (Xch mutants). The mutations were located in the 55' region of the chromosome, between the markers met-9011 and pyrD.

Siderophore activity of pyoverdin for Pseudomonas aeruginosa

Pseudomonas aeruginosa produces an extracellular compound with yellowish green fluorescence, called pyoverdin, which functions as a siderophore. The production of pyoverdin, formerly called fluorescein, is concomitant with the production of another siderophore, pyochelin. Pyoverdin is produced by P. aeruginosa in several forms, some of which were separated on gel filtration columns and on reverse-phase, high-pressure liquid chromatography columns. An active form of iron-free pyoverdin was purified to homogeneity. The elution of pyoverdin from the columns was monitored for absorbance, fluorescence, and siderophore activities. These activities, iron binding, and the stimulation of bacterial iron transport indicated that pyoverdin can function as a siderophore for P. aeruginosa. The siderophore function of pyoverdin may be related to the pathogenicity of this bacterium because pyoverdin stimulated growth not only in iron-deficient culture medium, but also in defined medium containing transferrin and in human serum or plasma.

Pseudomonas aeruginosa clearance in mice: comparison of tissue, strain, and corticosteroid effects

We used a murine model to determine whether chronic corticosteroid therapy has uniform effects on bacterial clearance processes in different tissues. After a 2-week regimen of oral prednisolone, Swiss Webster mice were challenged with Pseudomonas aeruginosa strain PAO1 or virulent derivatives of PAO1 (IP-8 and IT-10). Chronic corticosteroid therapy delayed the clearance of strain PAO1 from the peritoneal cavity. However, steroid treatment did not reduce the neutrophil influx, did not reduce the in vivo phagocytic capacity of neutrophils, and did not alter bactericidal activity of peritoneal exudate cells in vitro. Virulent isolates (IP-8 and IT-10) replicated in the peritoneal cavity in steroid-treated mice even though the neutrophil influx was similar to control mice. In contrast to the abnormal peritoneal clearance, all strains were rapidly cleared from the lungs of control and steroid-treated mice after aerosol challenge. Neutrophil influx into bronchoalveolar spaces was greater in steroid-treated mice than in control mice. All mice (control and steroid treated) survived these challenges, except for some steroid-treated mice infected intraperitoneally with IP-8. These results demonstrate that chronic steroid therapy alters bacterial clearance processes on the peritoneal surfaces to a greater extent than in the lower respiratory tract. The explanation for this altered clearance in the peritoneum is unclear, but cannot be explained by reductions in neutrophil migration to inflammatory stimuli. Therefore, the infectious risk associated with chronic corticosteroid therapy appears to depend on both the tissue and the virulence of the bacterial strain and may reflect alterations in clearance processes other than neutrophil migration.

Pseudomonas aeruginosa mutants altered in their sensitivity to the effect of iron on toxin A or elastase yields

Iron affects yields of toxin A, alkaline protease, elastase, pyochelin, and pyoverdin in Pseudomonas aeruginosa. Mutants of P. aeruginosa PAO1 resistant to the effect of iron on toxin (toxC) or elastase (elaC) yields were isolated. Two types of mutants were isolated: iron transport and iron regulatory mutants. The toxC regulatory mutants produced toxin A in medium containing iron; however, yields of elastase and alkaline protease remained sensitive to regulation by iron. The elaC regulatory mutants were resistant to the effect of iron on elastase yields, but toxin A and alkaline protease yields were decreased by iron, analogous to the parent strain. These data suggest that toxin A, elastase, and alkaline protease yields can be independently regulated by iron.

Effect of pyochelin on the virulence of Pseudomonas aeruginosa

A virulent isolate of Pseudomonas aeruginosa PAO1, which had been obtained from eight sequential intraperitoneal infections in mice compromised with iron and methotrexate, expressed greater lethality than the avirulent parent strain when both strains were injected into mice treated with iron. The present study demonstrates that pyochelin, a siderophore produced by P. aeruginosa, also increases the lethality of the virulent bacteria but not of the avirulent bacteria. Analysis of the growth and clearance of both virulent and avirulent strains in mice revealed that pyochelin increased the growth and lethality of virulent bacteria but only increased the survival of the avirulent bacteria. A streptomycin-dependent mutant of strain PAO1 (strd1) was used to demonstrate that pyochelin did not affect the clearance activity of mice. This strongly suggests that the effects of pyochelin in stimulating the persistence of avirulent bacteria and in increasing the lethality of virulent bacteria are due solely to the promotion of bacterial growth. Since the virulent bacteria were equivalent to the avirulent bacteria in utilizing pyochelin during in vitro growth in the presence of transferrin, it appears that the stimulation of growth by pyochelin allows the expression of additional virulence properties by the virulent bacteria.

Distribution of superoxide dismutase, catalase, and peroxidase activities among Treponema pallidum and other spirochetes

Representative members of Spirochaetales were surveyed for their content of superoxide dismutase (SOD), catalase, and peroxidase activities. Only Leptospira exhibited peroxidase activity. Obligately anaerobic cultivable Treponema and Spirochaeta possessed no SOD or peroxidative capabilities. Upon polyacrylamide gel electrophoresis, Spirochaeta aurantia, Borrelia hermsi, and five Leptospira biflexa serovars showed SOD activity associated with one electrophoretic band which was inhibited by H2O2, suggesting that they were iron-containing dismutases. These spirochetes could be distinguished by differences in relative mobilities of their SODs. SOD activity, but not catalase activity, was induced aerobically in S. aurantia. All Leptospira interrogans serovars and two L. biflexa serovars lacked significant SOD activity. These SOD-deficient strains of Leptospira, with one exception, possessed high levels of catalase activity. The Nichols strain of virulent Treponema pallidum possessed SOD and catalase activities, but lacked peroxidase activity. The SOD in T. pallidum exhibited two electrophoretic bands containing copper and zinc, and its relative mobility was identical to that of purified rabbit SOD. Immunization of sheep with purified rabbit SOD resulted in antiserum which inhibited both rabbit SOD and T. pallidum SOD assayed by spectrophotometric analysis or activity staining following polyacrylamide gel electrophoresis. In agarose gel diffusion, precipitin lines of identity were observed between purified rabbit SOD and cell extracts of T. pallidum. These data indicated that the SOD activity detected in T. pallidum was host derived.

Pyochelin: novel structure of an iron-chelating growth promoter for Pseudomonas aeruginosa

Pyochelin, an endogenous growth promoter that solubilizes ferric iron, has been isolated from Pseudomonas aeruginosa, including clinical strains. The structure of pyochelin has been assigned as 2-(2-o-hydroxyphenyl-2-thiazolin-4-yl)-3-methylthiazolidine-4-carboxylic acid and is of a different type from those previously assigned to siderophores (siderochromes) from bacteria. The assignment rests on 1H and 13C NMR data, high-resolution (including field desorption) mass spectrometry, and spectroscopic properties of synthetic model compounds. Pyochelin is presumed to be biosynthesized from salicylic acid and two moles of cysteine.

Distribution of glucose incorporated into macromolecular material by treponema pallidum

Treponema pallidum was observed to incorporate glucose carbons into lipids, ribonucleic acid, deoxyribonucleic acid, and protein. Only the glycerol portions of phosphatidylcholine and phosphatidylglycerol contained glucose-derived carbons. Incorporation of exogenous choline into phosphatidylcholine was detected. Glucose was incorporated into only the pentoses of nucleic acids. About 50% of the glucose incorporated into protein was present in only one amino acid, aspartate. Evidence suggests that aspartate synthesis could follow the conversion of phosphoenolpyruvate to oxalacetic acid by a guanosine 5'-diphosphate-dependent phosphoenolpyruvate carboxykinase.

Influence of oxygen on respiration and glucose catabolism by Treponema pallidum

Oxygen consumption by Treponema pallidum was observed to be glucose dependent. Treponemes consumed O2 to a low dissolved O2 concentration of 0.01 mumol of O2 per ml when respiration ceased. A fermentative degradation of glucose occurred during the maintenance of treponemes at 0.01 mumol of O2 per ml. Although the initial rate of respiration was independent of the dissolved O2 concentration, the respiration rate decreased upon prolonged incubation at 0.20 mumol of O2 per ml as compared with the respiration rate at 0.7 mumol of O2 per ml. Oxygen was determined to be the major electron acceptor during the oxidative metabolism of glucose. Acetate formation paralleled the respiration rate of the treponemes, whereas lactate production appeared to be independent of respiration. Accumulation of pyruvate occurred at 0.20 mumol of O2 per ml but not at 0.07 mumol/ml. Analyses of enzyme activities in cell-free extracts from treponemes maintained at either 0.07 or 0.20 mumol of O2 per ml for 4 h revealed a loss of pyruvate decarboxylase activity at the higher dissolved O2 concentration, suggesting the inactivation of pyruvate oxidase.