The metabolic reprogramming evoked by nitrosative stress triggers the anaerobic utilization of citrate in Pseudomonas fluorescens

Anti-inflammatory, Antioxidative, and Moisturizing Effects of Oxyceros horridus Lour. Ethanol Extract in Human Keratinocytes via the p38 Signaling Pathway

Skin is the largest and outermost organ in the human body; it serves as a vital defense mechanism against various external threats. Therefore, it is crucial to maintain its health through protection against harmful substances and adequate moisture levels. This study investigates the anti-inflammatory, antioxidant, and moisturizing properties of Oxyceros horridus Lour. (Oh-EE) in human keratinocytes. Oh-EE demonstrates potent antioxidant activity and effectively protects against oxidative stress induced by external stimuli such as UVB radiation and H2O2. Additionally, it exhibits significant anti-inflammatory effects proven by its ability to downregulate the expression of pro-inflammatory cytokines, namely COX-2 and IL-6. The study also explores the involvement of the AP-1 pathway, highlighting the ability of Oh-EE to suppress the expression of p38 and its upstream regulator, MKK3/6, under UVB-induced conditions. Interestingly, Oh-EE can activate the AP-1 pathway in the absence of external triggers. Furthermore, Oh-EE enhances skin moisture by upregulating the expression of key genes involved in skin hydration, namely HAS3 and FLG. These findings underscore the potential of Oh-EE as a versatile ingredient in skincare formulations, providing a range of skin benefits. Further research is warranted to comprehensively understand the underlying mechanisms through which Oh-EE exerts its effects.

Sub-lethal concentration of a colloidal nanosilver formulation (Silversol®) triggers dysregulation of iron homeostasis and nitrogen metabolism in multidrug resistant Pseudomonas aeruginosa

BACKGROUND

Pseudomonas aeruginosa is a notorious pathogen. Its multidrug resistant strains are listed among priority pathogens against whom discovery of novel antibacterial agents and, elucidation of new anti-pathogenicity mechanisms are urgently warranted. This study describes multiple antibacterial effects of a colloidal nano-silver formulation- Silversol® against a multi-drug resistant strain of P. aeruginosa.

RESULTS

Minimum inhibitory concentration (MIC) of Silversol® against P. aeruginosa was found to be 1.5 ppm; and at sub-MIC of 1 ppm, it was able to alter quorum-sensing regulated pigmentation (pyocanin 82%↓; pyoverdine 48%↑), exopolysaccharide synthesis (76%↑) and biofilm formation, susceptibility to antibiotics (streptomycin and augmentin), protein synthesis and export (65%↑), nitrogen metabolism (37%↑ nitrite accumulation), and siderophore production in this pathogen. Network analysis of the differentially expressed genes in the transcriptome of the silversol-treated bacterium identified ten genes as the potential molecular targets: norB, norD, nirS, nirF, nirM, nirQ, nosZ, nosY, narK1, and norE (all associated with nitrogen metabolism or denitrification). Three of them (norB, narK1, and norE) were also validated through RT-PCR.

CONCLUSIONS

Generation of nitrosative stress and disturbance of iron homeostasis were found to be the major mechanisms associated with anti-Pseudomonas activity of Silversol®.

Activation of multiple stress responses in Staphylococcus aureus substantially lowers the minimal inhibitory concentration when combining two novel antibiotic drug candidates

The past few decades have been plagued by an increasing number of infections caused by antibiotic resistant bacteria. To mitigate the rise in untreatable infections, we need new antibiotics with novel targets and drug combinations that reduce resistance development. The novel β-clamp targeting antimicrobial peptide BTP-001 was recently shown to have a strong additive effect in combination with the halogenated pyrrolopyrimidine JK-274. In this study, the molecular basis for this effect was examined by a comprehensive proteomic and metabolomic study of the individual and combined effects on Staphylococcus aureus. We found that JK-274 reduced activation of several TCA cycle enzymes, likely via increasing the cellular nitric oxide stress, and BTP-001 induced oxidative stress in addition to inhibiting replication, translation, and DNA repair processes. Analysis indicated that several proteins linked to stress were only activated in the combination and not in the single treatments. These results suggest that the strong additive effect is due to the activation of multiple stress responses that can only be triggered by the combined effect of the individual mechanisms. Importantly, the combination dose required to eradicate S. aureus was well tolerated and did not affect cell viability of immortalized human keratinocyte cells, suggesting a species-specific response. Our findings demonstrate the potential of JK-274 and BTP-001 as antibiotic drug candidates and warrant further studies.

Intranasal administration of sodium nitroprusside augments antigen-specific mucosal and systemic antibody production in mice

The coronavirus disease 2019, i.e., the COVID-19 pandemic, caused by a highly virulent and transmissible pathogen, has profoundly impacted global society. One approach to combat infectious diseases caused by pathogenic microbes is using mucosal vaccines, which can induce antigen-specific immune responses at both the mucosal and systemic sites. Despite its potential, the clinical implementation of mucosal vaccination is hampered by the lack of safe and effective mucosal adjuvants. Therefore, developing safe and effective mucosal adjuvants is essential for the fight against infectious diseases and the widespread clinical use of mucosal vaccines. In this study, we demonstrated the potent mucosal adjuvant effects of intranasal administration of sodium nitroprusside (SNP), a known nitric oxide (NO) donor, in mice. The results showed that intranasal administration of ovalbumin (OVA) in combination with SNP induced the production of OVA-specific immunoglobulin A in the mucosa and increased serum immunoglobulin G1 levels, indicating a T helper-2 (Th2)-type immune response. However, an analog of SNP, sodium ferrocyanide, which does not generate NO, failed to show any adjuvant effects, suggesting the critical role of NO generation in activating an immune response. In addition, SNPs facilitated the delivery of antigens to the lamina propria, where antigen-presenting cells are located, when co-administered with antigens, and also transiently elicited the expression of interleukin-6, interleukin-1β, granulocyte colony-stimulating factor, C-X-C motif chemokine ligand 1, and C-X-C motif chemokine ligand 2 in nasal tissue. These result suggest that SNP is a dual-functional formulation with antigen delivery capabilities to the lamina propria and the capacity to activate innate immunity. In summary, these results demonstrate the ability of SNP to induce immune responses via an antigen-specific Th2-type response, making it a promising candidate for further development as a mucosal vaccine formulation against infectious diseases.

Pixantrone Sensitizes Gram-Negative Pathogens to Rifampin

The emergence of bacterial drug resistance poses a severe threat to global public health. In particular, antimicrobial-resistant pathogens lead to a high rate of treatment failure and significantly increase mortality. Repurposing FDA-approved compounds to sensitize superbugs to conventional antibiotics provides a promising strategy to alleviate such crises. Pixantrone (PIX) has been approved for treating aggressive B-cell non-Hodgkin's lymphoma. By high-throughput drug screening, we profiled the synergistic activity between PIX and rifampin (RFP) against Gram-negative extensively drug-resistant isolates by checkerboard assay. Mechanistic studies demonstrated that PIX impacted the flagellum assembly, induced irreversible intracellular reactive oxygen species accumulation and disrupted proton motive force. In addition, the combination of PIX with RFP possesses effective antimicrobial activity against multidrug-resistant strains in vivo without detected toxicity. Collectively, these results reveal the potential of PIX in combination with RFP as a therapy option for refractory infections caused by Gram-negative pathogens. IMPORTANCE Bacterial resistance has become increasingly serious because of the widespread use and abuse of antibiotics. In particular, the emergence of multidrug-resistant bacteria has posed a serious threat to human public health. Drug repurposing, the process of finding new uses for existing drugs, provide a promising pathway to solve antimicrobial resistance. Compared to the development of novel antibiotics, this strategy leverages well-characterized pharmacology and toxicology of known drugs and is more cost-effective.

Variation in glucose metabolism under acidified sodium nitrite mediated nitrosative stress in Saccharomyces cerevisiae

AIMS

The work aimed to understand the important changes during glucose metabolism in Saccharomyces cerevisiae under acidified sodium nitrite (ac.NaNO₂ ) mediated nitrosative stress.

METHODS AND RESULTS

Confocal microscopy and fluorescence-activated cell sorting analysis were performed to investigate the generation of reactive nitrogen and oxygen species, and redox homeostasis under nitrosative stress was also characterized. Quantitative PCR analysis revealed that the expression of ADH genes was upregulated under such condition, whereas the ACO2 gene was downregulated. Some of the enzymes of the tricarboxylic acid cycle were partially inhibited, whereas malate metabolism and alcoholic fermentation were increased under nitrosative stress. Kinetics of ethanol production was also characterized. A network analysis was conducted to validate our findings. In the presence of ac.NaNO₂ , in vitro protein tyrosine nitration formation was checked by western blotting using pure alcohol dehydrogenase and aconitase.

CONCLUSIONS

Alcoholic fermentation rate was increased under stress condition and this altered metabolism might be conjoined with the defence machinery to overcome the nitrosative stress.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first work of this kind where the role of metabolism under nitrosative stress has been characterized in S. cerevisiae and it will provide a base to develop an alternative method of industrial ethanol production.

A Metabolic Network Mediating the Cycling of Succinate, a Product of ROS Detoxification into α-Ketoglutarate, an Antioxidant

Sulfur is an essential element for life. However, the soil microbe Pseudomonas (P.) fluorescens can survive in a low sulfur environment. When cultured in a sulfur-deficient medium, the bacterium reprograms its metabolic pathways to produce α-ketoglutarate (KG) and regenerate this keto-acid from succinate, a by-product of ROS detoxification. Succinate semialdehyde dehydrogenase (SSADH) and KG decarboxylase (KGDC) work in partnership to synthesize KG. This process is further aided by the increased activity of the enzymes glutamate decarboxylase (GDC) and γ-amino-butyrate transaminase (GABAT). The pool of succinate semialdehyde (SSA) generated is further channeled towards the formation of the antioxidant. Spectrophotometric analyses, HPLC experiments and electrophoretic studies with intact cells and cell-free extracts (CFE) pointed to the metabolites (succinate, SSA, GABA) and enzymes (SSADH, GDC, KGDC) contributing to this KG-forming metabolic machinery. Real-time polymerase chain reaction (RT-qPCR) revealed significant increase in transcripts of such enzymes as SSADH, GDC and KGDC. The findings of this study highlight a novel pathway involving keto-acids in ROS scavenging. The cycling of succinate into KG provides an efficient means of combatting an oxidative environment. Considering the central role of KG in biological processes, this metabolic network may be operative in other living systems.

A Common Feature of Pesticides: Oxidative Stress-The Role of Oxidative Stress in Pesticide-Induced Toxicity

Pesticides are important chemicals or biological agents that deter or kill pests. The use of pesticides has continued to increase as it is still considered the most effective method to reduce pests and increase crop growth. However, pesticides have other consequences, including potential toxicity to humans and wildlife. Pesticides have been associated with increased risk of cardiovascular disease, cancer, and birth defects. Labels on pesticides also suggest limiting exposure to these hazardous chemicals. Based on experimental evidence, various types of pesticides all seem to have a common effect, the induction of oxidative stress in different cell types and animal models. Pesticide-induced oxidative stress is caused by both reactive oxygen species (ROS) and reactive nitrogen species (RNS), which are associated with several diseases including cancer, inflammation, and cardiovascular and neurodegenerative diseases. ROS and RNS can activate at least five independent signaling pathways including mitochondrial-induced apoptosis. Limited in vitro studies also suggest that exogenous antioxidants can reduce or prevent the deleterious effects of pesticides.

Phosphate stress triggers the conversion of glycerol into l-carnitine in Pseudomonas fluorescens

Glycerol, a by-product of the biofuel industry is transformed into l-carnitine when the soil microbe Pseudomonas fluorescens is cultured in a phosphate-limited mineral medium (LP). Although the biomass yield was similar to that recorded in phosphate-sufficient cultures (HP), the rate of growth was slower. Phosphate was completely consumed in the LP cultures while in the HP media, approximately 35 % of the initial phosphate was detected at stationary phase of growth. The enhanced production of α-ketoglutarate (KG) in HP cultures supplemented with manganese was recently reported (Alhasawi et al., 2017). l-carnitine appeared to be a prominent metabolite in the spent fluid while the soluble cellular-free extract was characterized with peaks attributable to lysine, γ-butyrobetaine (GB), acetate and succinate in the LP cultures. Upon incubation with glycerol and NH₄Cl, the resting cells readily secreted l-carnitine and revealed the presence of such precursors like GB, lysine and methionine involved in the synthesis of this trimethylated moiety. Functional proteomic studies of select enzymes participating in tricarboxylic acid cycle (TCA), oxidative phosphorylation (OP), glyoxylate cycle and l-carnitine synthesis revealed a major metabolic reconfiguration evoked by phosphate stress. While isocitrate dehydrogenase-NAD⁺ dependent (ICDH-NAD⁺) and Complex I were markedly diminished, the activities of γ-butyrobetaine aldehyde dehydrogenase (GBADH) and l-carnitine dehydrogenase (CDH) were enhanced. Real-time quantitative polymerase chain reaction (RT-qPCR) analyses pointed to an increase in transcripts of the enzymes γ-butyrobetaine dioxygenase (bbox1), S-adenosylmethionine synthase (metK) and l-carnitine dehydrogenase (lcdH). The l-carnitine/γ-butyrobetaine antiporter (caiT) was enhanced more than 400-fold in the LP cultures compared to the HP controls. This metabolic reprogramming modulated by phosphate deprivation may provide an effective technology to transform glycerol, an industrial waste into valuable l-carnitine.

Possible mechanisms of HIV neuro-infection in alcohol use: Interplay of oxidative stress, inflammation, and energy interruption

Alcohol use and HIV-1 infection have a pervasive impact on brain function, which extends to the requirement, distribution, and utilization of energy within the central nervous system. This effect on neuroenergetics may explain, in part, the exacerbation of HIV-1 disease under the influence of alcohol, particularly the persistence of HIV-associated neurological complications. The objective of this review article is to highlight the possible mechanisms of HIV/AIDS progression in alcohol users from the perspective of oxidative stress, neuroinflammation, and interruption of energy metabolism. These include the hallmark of sustained immune cell activation and high metabolic energy demand by HIV-1-infected cells in the central nervous system, with at-risk alcohol use. Here, we discussed the point that the increase in energy supply requirement by HIV-1-infected neuroimmune cells as well as the deterrence of nutrient uptake across the blood-brain barrier significantly depletes the energy source and neuro-environment homeostasis in the CNS. We also described the mechanistic idea that comorbidity of HIV-1 infection and alcohol use can cause a metabolic shift and redistribution of energy usage toward HIV-1-infected neuroimmune cells, as shown in neuropathological evidence. Under such an imbalanced neuro-environment, meaningless energy waste is expected in infected cells, along with unnecessary malnutrition in non-infected neuronal cells, which is likely to accelerate HIV neuro-infection progression in alcohol use. Thus, it will be important to consider the factor of nutrients/energy imbalance in formulating treatment strategies to help impede the progression of HIV-1 disease and associated neurological disorders in alcohol use.

Beyond mitochondria: Alternative energy-producing pathways from all strata of life

It is well-established that mitochondria are the powerhouses of the cell, producing adenosine triphosphate (ATP), the universal energy currency. However, the most significant strengths of the electron transport chain (ETC), its intricacy and efficiency, are also its greatest downfalls. A reliance on metal complexes (FeS clusters, hemes), lipid moities such as cardiolipin, and cofactors including alpha-lipoic acid and quinones render oxidative phosphorylation vulnerable to environmental toxins, intracellular reactive oxygen species (ROS) and fluctuations in diet. To that effect, it is of interest to note that temporal disruptions in ETC activity in most organisms are rarely fatal, and often a redundant number of failsafes are in place to permit continued ATP production when needed. Here, we highlight the metabolic reconfigurations discovered in organisms ranging from parasitic Entamoeba to bacteria such as pseudomonads and then complex eukaryotic systems that allow these species to adapt to and occasionally thrive in harsh environments. The overarching aim of this review is to demonstrate the plasticity of metabolic networks and recognize that in times of duress, life finds a way.

Biochemical pathways to α-ketoglutarate, a multi-faceted metabolite

α-Ketoglutarate (AKG) also known as 2-oxoglutarate is an essential metabolite in virtually all organisms as it participates in a variety of biological processes including anti-oxidative defence, energy production, signalling modules, and genetic modification. This keto-acid also possesses immense commercial value as it is utilized as a nutritional supplement, a therapeutic agent, and a precursor to a variety of value-added products such as ethylene and heterocyclic compounds. Hence, the generation of KG in a sustainable and environmentally-neutral manner is a major ongoing research endeavour. In this mini-review, the enzymatic systems and the metabolic networks mediating the synthesis of AKG will be described. The importance of such enzymes as isocitrate dehydrogenase (ICDH), glutamate dehydrogenase (GDH), succinate semialdehyde dehydrogenase (SSADH) and transaminases that directly contribute to the formation of KG will be emphasized. The efficacy of microbial systems in providing an effective platform to generate this moiety and the molecular strategies involving genetic manipulation, abiotic stress and nutrient supplementation that result in the optimal production of AKG will be evaluated. Microbial systems and their components acting via the metabolic networks and the resident enzymes are well poised to provide effective biotechnological tools that can supply renewable AKG globally.

Metabolic manipulation by Pseudomonas fluorescens: a powerful stratagem against oxidative and metal stress

Metabolism is the foundation of all living organisms and is at the core of numerous if not all biological processes. The ability of an organism to modulate its metabolism is a central characteristic needed to proliferate, to be dormant and to survive any assault. Pseudomonas fluorescens is bestowed with a uniquely versatile metabolic framework that enables the microbe to adapt to a wide range of conditions including disparate nutrients and toxins. In this mini-review we elaborate on the various metabolic reconfigurations evoked by this microbial system to combat reactive oxygen/nitrogen species and metal stress. The fine-tuning of the NADH/NADPH homeostasis coupled with the production of α-keto-acids and ATP allows for the maintenance of a reductive intracellular milieu. The metabolic networks propelling the synthesis of metabolites like oxalate and aspartate are critical to keep toxic metals at bay. The biochemical processes resulting from these defensive mechanisms provide molecular clues to thwart infectious microbes and reveal elegant pathways to generate value-added products.

The effects of gasotransmitters on bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD), which remains a major clinical problem for preterm infants, is caused mainly by hyperoxia, mechanical ventilation and inflammation. Many approaches have been developed with the aim of decreasing the incidence of or alleviating BPD, but effective methods are still lacking. Gasotransmitters, a type of small gas molecule that can be generated endogenously, exert a protective effect against BPD-associated lung injury; nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S) are three such gasotransmitters. The protective effects of NO have been extensively studied in animal models of BPD, but the results of these studies are inconsistent with those of clinical trials. NO inhalation seems to have no effect on BPD, although side effects have been reported. NO inhalation is not recommended for BPD treatment in preterm infants, except those with severe pulmonary hypertension. Both CO and H₂S decreased lung injury in BPD rodent models in preclinical studies. Another small gas molecule, hydrogen, exerts a protective effect against BPD. The nuclear factor erythroid-derived 2 (Nrf2)/heme oxygenase-1 (HO-1) axis seems to play a central role in the protective effect of these gasotransmitters on BPD. Gasotransmitters play important roles in mammals, but further clinical trials are needed to explore their effects on BPD.

Metabolic adaptation and NADPH homeostasis evoked by a sulfur-deficient environment in Pseudomonas fluorescens

Sulfur is essential for all living organisms due to its ability to mediate a variety of enzymatic reactions, signalling networks, and redox processes. The interplay between sulfhydryl group (SH) and disulfide bond (S-S) is central to the maintenance of intracellular oxidative balance. Although most aerobic organisms succumb to sulfur starvation, the nutritionally versatile soil microbe Pseudomonas fluorescens elaborates an intricate metabolic reprogramming in order to adapt to this challenge. When cultured in a sulfur-deficient medium with glutamine as the sole carbon and nitrogen source, the microbe reconfigures its metabolism aimed at the enhanced synthesis of NADPH, an antioxidant and the limited production of NADH, a pro-oxidant. While oxidative phosphorylation (OXPHOS) and tricarboxylic acid (TCA) cycle, metabolic modules known to generate reactive oxygen species are impeded, the activities NADPH-producing enzymes such as malic enzyme, and glutamate dehydrogenase (GDH) NADP-dependent are increased. The α-ketoglutarate (KG) generated from glutamine rapidly enters the TCA cycle via α-ketoglutarate dehydrogenase (KGDH), an enzyme that was prominent in the control cultures. In the S-deficient media, the severely impeded KGDH coupled with the increased activity of the reversible isocitrate dehydrogenase (ICDH) that fixes KG into isocitrate in the presence of NADH and HCO₃^- ensures a constant supply of this critical tricarboxylic acid. The up-regulation of ICDH-NADP dependent in the soluble fraction of the cells obtained from the S-deficient media results in enhanced NADPH synthesis, a reaction aided by the concomitant increase in NAD kinase activity. The latter converts NAD into NADP in the presence of ATP. Taken together, the data point to a metabolic network involving isocitrate, α-KG, and ICDH that converts NADH into NADPH in P. fluorescens subjected to a S-deprived environment.

Isocitrate Lyase and Succinate Semialdehyde Dehydrogenase Mediate the Synthesis of α-Ketoglutarate in Pseudomonas fluorescens

Glycerol is an important by-product of the biodiesel industry and its transformation into value-added products like keto acids is being actively pursued in order to improve the efficacy of this renewable energy sector. Here, we report that the enhanced production of α-ketoglutarate (KG) effected by Pseudomonas fluorescens in a mineral medium supplemented with manganese (Mn) is propelled by the increased activities of succinate semialdehyde dehydrogenase (SSADH), γ-aminobutyric acid aminotransaminase (GABAT), and isocitrate lyase (ICL). The latter generates glyoxylate and succinate two key metabolites involved in this process. Fumarate reductase (FRD) also aids in augmenting the pool of succinate, a precursor of succinate semialdehyde (SSA). The latter is then carboxylated to KG with the assistance of α-ketoglutarate decarboxylase (KDC). These enzymes work in tandem to ensure copious secretion of the keto acid. When incubated with glycerol in the presence of bicarbonate (HCO3−), cell-free extracts readily produce KG with a metabolite fingerprint attributed to glutamate, γ-aminobutyric acid (GABA), succinate and succinate semialdehyde. Further targeted metabolomic and functional proteomic studies with high-performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR) and gel electrophoresis techniques provided molecular insights into this KG-generating machinery. Real-time quantitative polymerase chain reaction (RT-qPCR) analyses revealed the transcripts responsible for ICL and SSADH were elevated in the Mn-supplemented cultures. This hitherto unreported metabolic network where ICL and SSADH orchestrate the enhanced production of KG from glycerol, provides an elegant means of converting an industrial waste into a keto acid with wide-ranging application in the medical, cosmetic, and chemical sectors.

CitE Enzymes Are Essential for Mycobacterium tuberculosis to Establish Infection in Macrophages and Guinea Pigs

Bacterial citrate lyase activity has been demonstrated in various eukaryotes, bacteria and archaea, underscoring their importance in energy metabolism of the cell. While the bacterial citrate lyase comprises of three different subunits, M. tuberculosis genome lacks CitD and CitF subunits of citrate lyase complex but encodes for 2 homologs of CitE subunits, Rv2498c and Rv3075c. Using temperature sensitive mycobacteriophages, we were able to generate both single and double citE mutant strains of M. tuberculosis. The survival experiments revealed increased susceptibility of the double mutant strain to oxidative stress in comparison to the parental strain. Also, simultaneous deletion of both citE1 and citE2 in M. tuberculosis genome resulted in impairment of intracellular replication in macrophages. The double mutant strain displayed reduced growth in lungs and spleens of guinea pigs. This is the first study demonstrating that M. tuberculosis critically requires CitE subunits of citrate lyase for pathogenesis. Taken together, these findings position these enzymes as potential targets for development of anti-tubercular small molecules.

Reactive nitrogen species (RNS)-resistant microbes: adaptation and medical implications

Nitrosative stress results from an increase in reactive nitrogen species (RNS) within the cell. Though the RNS - nitric oxide (·NO) and peroxynitrite (ONOO-) - play pivotal physiological roles, at elevated concentrations, these moieties can be poisonous to both prokaryotic and eukaryotic cells alike due to their capacity to disrupt a variety of essential biological processes. Numerous microbes are known to adapt to nitrosative stress by elaborating intricate strategies aimed at neutralizing RNS. In this review, we will discuss both the enzymatic systems dedicated to the elimination of RNS as well as the metabolic networks that are tailored to generate RNS-detoxifying metabolites - α-keto-acids. The latter has been demonstrated to nullify RNS via non-enzymatic decarboxylation resulting in the production of a carboxylic acid, many of which are potent signaling molecules. Furthermore, as aerobic energy production is severely impeded during nitrosative stress, alternative ATP-generating modules will be explored. To that end, a holistic understanding of the molecular adaptation to nitrosative stress, reinforces the notion that neutralization of toxicants necessitates significant metabolic reconfiguration to facilitate cell survival. As the alarming rise in antimicrobial resistant pathogens continues unabated, this review will also discuss the potential for developing therapies that target the alternative ATP-generating machinery of bacteria.

The role of glutamine synthetase in energy production and glutamine metabolism during oxidative stress

Oxidative stress is known to severely impede aerobic adenosine triphosphate (ATP) synthesis. However, the metabolically-versatile Pseudomonas fluorescens survives this challenge by invoking alternative ATP-generating networks. When grown in a medium with glutamine as the sole organic nutrient in the presence of H₂O₂, the microbe utilizes glutamine synthetase (GS) to modulate its energy budget. The activity of this enzyme that mediates the release of energy stored in glutamine was sharply increased in the stressed cells compared to the controls. The enhanced activities of such enzymes as acetate kinase, adenylate kinase and nucleotide diphosphate kinase ensured the efficacy of this ATP producing-machine by transferring the high energy phosphate. The elevated amounts of phosphoenol pyruvate carboxylase and pyruvate orthophosphate dikinase recorded in the H₂O₂ exposed cells provided another route to ATP independent of the reduction of O₂. This is the first demonstration of a metabolic pathway involving GS dedicated to ATP synthesis. The phospho-transfer network that is pivotal to the survival of the microorganism under oxidative stress may reveal therapeutic targets against infectious microbes reliant on glutamine for their proliferation.

The Role of Reactive Oxygen Species in Antibiotic-Mediated Killing of Bacteria

Recently, it was proposed that there is a common mechanism behind the activity of bactericidal antibiotics, involving the production of reactive oxygen species (ROS). However, the involvement of ROS in antibiotic-mediated killing has become the subject of much debate. In the present review, we provide an overview of the data supporting the ROS hypothesis; we also present data that explain the contradictory results often obtained when studying antibiotic-induced ROS production. For this latter aspect we will focus on the importance of taking the experimental setup into consideration and on the importance of some technical aspects of the assays typically used. Finally, we discuss the link between ROS production and toxin-antitoxin modules, and present an overview of implications for treatment.

PGPR-mediated expression of salt tolerance gene in soybean through volatiles under sodium nitroprusside

Increasing evidence shows that nitric oxide (NO), a typical signaling molecule plays important role in development of plant and in bacteria-plant interaction. In the present study, we tested the effect of sodium nitroprusside (SNP)-a nitric oxide donor, on bacterial metabolism and its role in establishment of PGPR-plant interaction under salinity condition. In the present study, we adopted methods namely, biofilm formation assay, GC-MS analysis of bacterial volatiles, chemotaxis assay of root exudates (REs), measurement of electrolyte leakage and lipid peroxidation, and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) for gene expression. GC-MS analysis revealed that three new volatile organic compounds (VOCs) were expressed after treatment with SNP. Two VOCs namely, 4-nitroguaiacol and quinoline were found to promote soybean seed germination under 100 mM NaCl stress. Chemotaxis assay revealed that SNP treatment, altered root exudates profiling (SS-RE), found more attracted to Pseudomonas simiae bacterial cells as compared to non-treated root exudates (S-RE) under salt stress. Expression of Peroxidase (POX), catalase (CAT), vegetative storage protein (VSP), and nitrite reductase (NR) genes were up-regulated in T6 treatment seedlings, whereas, high affinity K+ transporter (HKT1), lipoxygenase (LOX), polyphenol oxidase (PPO), and pyrroline-5-carboxylate synthase (P5CS) genes were down-regulated under salt stress. The findings suggest that NO improves the efficiency and establishment of PGPR strain in the plant environment during salt condition. This strategy may be applied on soybean plants to increase their growth during salinity stress.

Phospho-transfer networks and ATP homeostasis in response to an ineffective electron transport chain in Pseudomonas fluorescens

Although oxidative stress is known to impede the tricarboxylic acid (TCA) cycle and oxidative phosphorylation, the nutritionally-versatile microbe, Pseudomonas fluorescens has been shown to proliferate in the presence of hydrogen peroxide (H2O2) and nitrosative stress. In this study we demonstrate the phospho-transfer system that enables this organism to generate ATP was similar irrespective of the carbon source utilized. Despite the diminished activities of enzymes involved in the TCA cycle and in the electron transport chain (ETC), the ATP levels did not appear to be significantly affected in the stressed cells. Phospho-transfer networks mediated by acetate kinase (ACK), adenylate kinase (AK), and nucleoside diphosphate kinase (NDPK) are involved in maintaining ATP homeostasis in the oxidatively-challenged cells. This phospho-relay machinery orchestrated by substrate-level phosphorylation is aided by the up-regulation in the activities of such enzymes like phosphoenolpyruvate carboxylase (PEPC), pyruvate orthophosphate dikinase (PPDK), and phosphoenolpyruvate synthase (PEPS). The enhanced production of phosphoenolpyruvate (PEP) and pyruvate further fuel the synthesis of ATP. Taken together, this metabolic reconfiguration enables the organism to fulfill its ATP need in an O2-independent manner by utilizing an intricate phospho-wire module aimed at maximizing the energy potential of PEP with the participation of AMP.

Metabolic profiling of residents in the vicinity of a petrochemical complex

No previous studies have simultaneously measured the biomarkers of environmental exposure and metabolome perturbation in residents affected by industrial pollutants. This study aimed to investigate the metabolic effects of environmental pollutants such as vanadium and polycyclic aromatic hydrocarbons (PAHs) on residents in the vicinity of a petrochemical complex. The study subjects were 160 residents, including 80 high-exposure subjects exposed to high levels of vanadium and PAHs and 80 age- and gender-matched low-exposure subjects living within a 40-km radius of a petrochemical complex. The exposure biomarkers vanadium and 1-hydroxypyrene and four oxidative/nitrosative stress biomarkers were measured in these subjects. Plasma samples from the study subjects were also analyzed using (1)H NMR spectroscopy for metabolic profiling. The results showed that the urinary levels of vanadium and 1-hydroxypyrene in the high-exposure subjects were 40- and 20-fold higher, respectively, than those in the low-exposure subjects. Higher urinary levels of stress biomarkers, including 8-OHdG, HNE-MA, 8-isoPF2α, and 8-NO2Gua, were also observed among the high-exposure subjects compared with the low-exposure subjects. Partial least squares discriminant analysis of the plasma metabolome demonstrated a clear separation between the high- and low-exposure subjects; the intensities of amino acids and carbohydrate metabolites were lower in the high-exposure subjects compared with the low-exposure subjects. The exposure to vanadium and PAHs may cause a reduction in the levels of amino acids and carbohydrates by elevating PPAR and insulin signaling, as well as oxidative/nitrosative stress.

Response to Gaseous NO2 Air Pollutant of P. fluorescens Airborne Strain MFAF76a and Clinical Strain MFN1032

Human exposure to nitrogen dioxide (NO₂), an air pollutant of increasing interest in biology, results in several toxic effects to human health and also to the air microbiota. The aim of this study was to investigate the bacterial response to gaseous NO₂. Two Pseudomonas fluorescens strains, namely the airborne strain MFAF76a and the clinical strain MFN1032 were exposed to 0.1, 5, or 45 ppm concentrations of NO₂, and their effects on bacteria were evaluated in terms of motility, biofilm formation, antibiotic resistance, as well as expression of several chosen target genes. While 0.1 and 5 ppm of NO₂did not lead to any detectable modification in the studied phenotypes of the two bacteria, several alterations were observed when the bacteria were exposed to 45 ppm of gaseous NO₂. We thus chose to focus on this high concentration. NO₂-exposed P. fluorescens strains showed reduced swimming motility, and decreased swarming in case of the strain MFN1032. Biofilm formed by NO₂-treated airborne strain MFAF76a showed increased maximum thickness compared to non-treated cells, while NO₂ had no apparent effect on the clinical MFN1032 biofilm structure. It is well known that biofilm and motility are inversely regulated by intracellular c-di-GMP level. The c-di-GMP level was however not affected in response to NO₂ treatment. Finally, NO₂-exposed P. fluorescens strains were found to be more resistant to ciprofloxacin and chloramphenicol. Accordingly, the resistance nodulation cell division (RND) MexEF-OprN efflux pump encoding genes were highly upregulated in the two P. fluorescens strains. Noticeably, similar phenotypes had been previously observed following a NO treatment. Interestingly, an hmp-homolog gene in P. fluorescens strains MFAF76a and MFN1032 encodes a NO dioxygenase that is involved in NO detoxification into nitrites. Its expression was upregulated in response to NO₂, suggesting a possible common pathway between NO and NO₂ detoxification. Taken together, our study provides evidences for the bacterial response to NO₂ toxicity.

Metabolic networks to generate pyruvate, PEP and ATP from glycerol in Pseudomonas fluorescens

Glycerol is a major by-product of the biodiesel industry. In this study we report on the metabolic networks involved in its transformation into pyruvate, phosphoenolpyruvate (PEP) and ATP. When the nutritionally-versatile Pseudomonas fluorescens was exposed to hydrogen peroxide (H2O2) in a mineral medium with glycerol as the sole carbon source, the microbe reconfigured its metabolism to generate adenosine triphosphate (ATP) primarily via substrate-level phosphorylation (SLP). This alternative ATP-producing stratagem resulted in the synthesis of copious amounts of PEP and pyruvate. The production of these metabolites was mediated via the enhanced activities of such enzymes as pyruvate carboxylase (PC) and phosphoenolpyruvate carboxylase (PEPC). The high energy PEP was subsequently converted into ATP with the aid of pyruvate phosphate dikinase (PPDK), phosphoenolpyruvate synthase (PEPS) and pyruvate kinase (PK) with the concomitant formation of pyruvate. The participation of the phospho-transfer enzymes like adenylate kinase (AK) and acetate kinase (ACK) ensured the efficiency of this O2-independent energy-generating machinery. The increased activity of glycerol dehydrogenase (GDH) in the stressed bacteria provided the necessary precursors to fuel this process. This H2O2-induced anaerobic life-style fortuitously evokes metabolic networks to an effective pathway that can be harnessed into the synthesis of ATP, PEP and pyruvate. The bioconversion of glycerol to pyruvate will offer interesting economic benefit.

Leishmania carbon metabolism in the macrophage phagolysosome- feast or famine?

A number of medically important microbial pathogens target and proliferate within macrophages and other phagocytic cells in their mammalian hosts. While the majority of these pathogens replicate within the host cell cytosol or non-hydrolytic vacuolar compartments, a few, including protists belonging to the genus Leishmania, proliferate long-term within mature lysosome compartments.  How these parasites achieve this feat remains poorly defined. In this review, we highlight recent studies that suggest that Leishmania virulence is intimately linked to programmed changes in the growth rate and carbon metabolism of the obligate intra-macrophage stages. We propose that activation of a slow growth and a stringent metabolic response confers resistance to multiple stresses (oxidative, temperature, pH), as well as both nutrient limitation and nutrient excess within this niche. These studies highlight the importance of metabolic processes as key virulence determinants in Leishmania.

Dysfunctional mitochondrial bioenergetics and the pathogenesis of hepatic disorders

The liver is involved in a variety of critical biological functions including the homeostasis of glucose, fatty acids, amino acids, and the synthesis of proteins that are secreted in the blood. It is also at the forefront in the detoxification of noxious metabolites that would otherwise upset the functioning of the body. As such, this vital component of the mammalian system is exposed to a notable quantity of toxicants on a regular basis. It therefore comes as no surprise that there are over a hundred disparate hepatic disorders, encompassing such afflictions as fatty liver disease, hepatitis, and liver cancer. Most if not all of liver functions are dependent on energy, an ingredient that is primarily generated by the mitochondrion, the power house of all cells. This organelle is indispensable in providing adenosine triphosphate (ATP), a key effector of most biological processes. Dysfunctional mitochondria lead to a shortage in ATP, the leakage of deleterious reactive oxygen species (ROS), and the excessive storage of fats. Here we examine how incapacitated mitochondrial bioenergetics triggers the pathogenesis of various hepatic diseases. Exposure of liver cells to detrimental environmental hazards such as oxidative stress, metal toxicity, and various xenobiotics results in the inactivation of crucial mitochondrial enzymes and decreased ATP levels. The contribution of the latter to hepatic disorders and potential therapeutic cues to remedy these conditions are elaborated.

A novel ATP-generating machinery to counter nitrosative stress is mediated by substrate-level phosphorylation

BACKGROUND

It is well-known that elevated amounts of nitric oxide and other reactive nitrogen species (RNS) impact negatively on the tricarboxylic acid (TCA) cycle and oxidative phosphorylation. These perturbations severely compromise O2-dependent energy production. While bacteria are known to adapt to RNS, a key tool employed by macrophages to combat infections, the exact mechanisms are unknown.

METHODS

The bacterium was cultured in a defined mineral medium and cell-free extracts obtained at the same growth phase were utilized for various biochemical studies Blue native polyacrylamide gel electrophoresis followed by in-gel activity assays, high performance liquid chromatography and co-immunoprecipitaton are applied to investigate the effects of RNS on the model microbe Pseudomonas fluorescens.

RESULTS

Citrate is channeled away from the tricarboxylic acid cycle using a novel metabolon consisting of citrate lyase (CL), phosphoenolpyruvate carboxylase (PEPC) and pyruvate phosphate dikinase (PPDK). This metabolic engine comprising three disparate enzymes appears to transiently assemble as a supercomplex aimed at ATP synthesis. The up-regulation in the activities of adenylate kinase (AK) and nucleoside diphosphate kinase (NDPK) ensured the efficacy of this ATP-making machine.

CONCLUSION

Microbes may escape the effects of nitrosative stress by re-engineering metabolic networks in order to generate and store ATP anaerobically when the electron transport chain is defective.

GENERAL SIGNIFICANCE

The molecular configuration described herein provides further understanding of how metabolism plays a key role in the adaptation to nitrosative stress and reveals novel targets that will inform the development of antimicrobial agents to counter RNS-resistant pathogens.

Deciphering nitric oxide stress in bacteria with quantitative modeling

Many pathogens depend on nitric oxide (NO•) detoxification and repair to establish an infection, and inhibitors of these systems are under investigation as next-generation antibiotics. Because of the broad reactivity of NO• and its derivatives with biomolecules, a deep understanding of how pathogens sense and respond to NO•, as an integrated system, has been elusive. Quantitative kinetic modeling has been proposed as a method to enhance analysis and understanding of NO• stress at the systems-level. Here we review the motivation for, current state of, and future prospects of quantitative modeling of NO• stress in bacteria, and suggest that such mathematical approaches would prove equally useful in the study of other broadly reactive antimicrobials, such as hydrogen peroxide (H2O2).

Fumarate metabolism and ATP production in Pseudomonas fluorescens exposed to nitrosative stress

Although nitrosative stress is known to severely impede the ability of living systems to generate adenosine triphosphate (ATP) via oxidative phosphorylation, there is limited information on how microorganisms fulfill their energy needs in order to survive reactive nitrogen species (RNS). In this study we demonstrate an elaborate strategy involving substrate-level phosphorylation that enables the soil microbe Pseudomonas fluorescens to synthesize ATP in a defined medium with fumarate as the sole carbon source. The enhanced activities of such enzymes as phosphoenolpyruvate carboxylase and pyruvate phosphate dikinase coupled with the increased activities of phospho-transfer enzymes like adenylate kinase and nucleoside diphophate kinase provide an effective strategy to produce high energy nucleosides in an O2-independent manner. The alternate ATP producing machinery is fuelled by the precursors derived from fumarate with the aid of fumarase C and fumarate reductase. This metabolic reconfiguration is key to the survival of P. fluorescens and reveals potential targets against RNS-resistant organisms.

Zinc toxicity and ATP production in Pseudomonas fluorescens

AIMS

To identify the molecular networks in Pseudomonas fluorescens that convey resistance to toxic concentrations of Zn, a common pollutant and hazard to biological systems.

METHODS AND RESULTS

Pseudomonas fluorescens strain ATCC 13525 was cultured in growth medium with millimolar concentrations of Zn. Enzymatic activities and metabolite levels were monitored with the aid of in-gel activity assays and high-performance liquid chromatography, respectively. As oxidative phosphorylation was rendered ineffective, the assimilation of citric acid mediated sequentially by citrate lyase (CL), phosphoenolpyruvate carboxylase (PEPC) and pyruvate phosphate dikinase (PPDK) appeared to play a key role in ATP synthesis via substrate-level phosphorylation (SLP). Enzymes generating the antioxidant, reduced nicotinamide adenine dinucleotide phosphate (NADPH) were enhanced, while metabolic modules mediating the formation of the pro-oxidant, reduced nicotinamide adenine dinucleotide (NADH) were downregulated.

CONCLUSIONS

Pseudomonas fluorescens reengineers its metabolic networks to generate ATP via SLP, a stratagem that allows the microbe to compensate for an ineffective electron transport chain provoked by excess Zn.

SIGNIFICANCE AND IMPACT OF THE STUDY

The molecular insights described here are critical in devising strategies to bioremediate Zn-polluted environments.