Extracellular DNA Promotes Efficient Extracellular Electron Transfer by Pyocyanin in Pseudomonas aeruginosa Biofilms.

Redox cycling of extracellular electron shuttles can enable the metabolic activity of subpopulations within multicellular bacterial biofilms that lack direct access to electron acceptors or donors. How these shuttles catalyze extracellular electron transfer (EET) within biofilms without being lost to the environment has been a long-standing question. Here, we show that phenazines mediate efficient EET through interactions with extracellular DNA (eDNA) in Pseudomonas aeruginosa biofilms. Retention of pyocyanin (PYO) and phenazine carboxamide in the biofilm matrix is facilitated by eDNA binding. In vitro, different phenazines can exchange electrons in the presence or absence of DNA and can participate directly in redox reactions through DNA. In vivo, biofilm eDNA can also support rapid electron transfer between redox active intercalators. Together, these results establish that PYO:eDNA interactions support an efficient redox cycle with rapid EET that is faster than the rate of PYO loss from the biofilm.

Excess Translation of Epigenetic Regulators Contributes to Fragile X Syndrome and Is Alleviated by Brd4 Inhibition.

Fragile X syndrome (FXS) is a leading genetic cause of intellectual disability and autism. FXS results from the loss of function of fragile X mental retardation protein (FMRP), which represses translation of target transcripts. Most of the well-characterized target transcripts of FMRP are synaptic proteins, yet targeting these proteins has not provided effective treatments. We examined a group of FMRP targets that encode transcriptional regulators, particularly chromatin-associated proteins. Loss of FMRP in mice results in widespread changes in chromatin regulation and aberrant gene expression. To determine if targeting epigenetic factors could reverse phenotypes associated with the disorder, we focused on Brd4, a BET protein and chromatin reader targeted by FMRP. Inhibition of Brd4 function alleviated many of the phenotypes associated with FXS. We conclude that loss of FMRP results in significant epigenetic misregulation and that targeting transcription via epigenetic regulators like Brd4 may provide new treatments for FXS.

Chemosensation of bacterial secondary metabolites modulates neuroendocrine signaling and behavior of C. elegans.

Discrimination between pathogenic and beneficial microbes is essential for host organism immunity and homeostasis. Here, we show that chemosensory detection of two secondary metabolites produced by Pseudomonas aeruginosa modulates a neuroendocrine signaling pathway that promotes avoidance behavior in the simple animal host Caenorhabditis elegans. Secondary metabolites phenazine-1-carboxamide and pyochelin activate a G-protein-signaling pathway in the ASJ chemosensory neuron pair that induces expression of the neuromodulator DAF-7/TGF-ß. DAF-7, in turn, activates a canonical TGF-ß signaling pathway in adjacent interneurons to modulate aerotaxis behavior and promote avoidance of pathogenic P. aeruginosa. Our data provide a chemical, genetic, and neuronal basis for how the behavior and physiology of a simple animal host can be modified by the microbial environment and suggest that secondary metabolites produced by microbes may provide environmental cues that contribute to pathogen recognition and host survival.

Genetically dissecting the electron transport chain of a soil bacterium reveals a generalizable mechanism for biological phenazine-1-carboxylic acid oxidation.

The capacity for bacterial extracellular electron transfer via secreted metabolites is widespread in natural, clinical, and industrial environments. Recently, we discovered the biological oxidation of phenazine-1-carboxylic acid (PCA), the first example of biological regeneration of a naturally produced extracellular electron shuttle. However, it remained unclear how PCA oxidation was catalyzed. Here, we report the mechanism, which we uncovered by genetically perturbing the branched electron transport chain (ETC) of the soil isolate Citrobacter portucalensis MBL. Biological PCA oxidation is coupled to anaerobic respiration with nitrate, fumarate, dimethyl sulfoxide, or trimethylamine-N-oxide as terminal electron acceptors. Genetically inactivating the catalytic subunits for all redundant complexes for a given terminal electron acceptor abolishes PCA oxidation. In the absence of quinones, PCA can still donate electrons to certain terminal reductases, albeit much less efficiently. In C. portucalensis MBL, PCA oxidation is largely driven by flux through the ETC, which suggests a generalizable mechanism that may be employed by any anaerobically respiring bacterium with an accessible cytoplasmic membrane. This model is supported by analogous genetic experiments during nitrate respiration by Pseudomonas aeruginosa.

Spatial heterogeneity in biofilm metabolism elicited by local control of phenazine methylation.

Within biofilms, gradients of electron acceptors such as oxygen stimulate the formation of physiological subpopulations. This heterogeneity can enable cross-feeding and promote drug resilience, features of the multicellular lifestyle that make biofilm-based infections difficult to treat. The pathogenic bacterium Pseudomonas aeruginosa produces pigments called phenazines that can support metabolic activity in hypoxic/anoxic biofilm subzones, but these compounds also include methylated derivatives that are toxic to their producer under some conditions. In this study, we uncover roles for the global regulators RpoS and Hfq/Crc in controlling the beneficial and detrimental effects of methylated phenazines in biofilms. Our results indicate that RpoS controls phenazine methylation by modulating activity of the carbon catabolite repression pathway, in which the Hfq/Crc complex inhibits translation of the phenazine methyltransferase PhzM. We find that RpoS indirectly inhibits expression of CrcZ, a small RNA that binds to and sequesters Hfq/Crc, specifically in the oxic subzone of P. aeruginosa biofilms. Deletion of rpoS or crc therefore leads to overproduction of methylated phenazines, which we show leads to increased metabolic activity-an apparent beneficial effect-in hypoxic/anoxic subpopulations within biofilms. However, we also find that under specific conditions, biofilms lacking RpoS and/or Crc show increased sensitivity to phenazines indicating that the increased metabolic activity in these mutants comes at a cost. Together, these results suggest that complex regulation of PhzM allows P. aeruginosa to simultaneously exploit the benefits and limit the toxic effects of methylated phenazines.

The chemical ecology of coumarins and phenazines affects iron acquisition by pseudomonads.

Secondary metabolites are important facilitators of plant-microbe interactions in the rhizosphere, contributing to communication, competition, and nutrient acquisition. However, at first glance, the rhizosphere seems full of metabolites with overlapping functions, and we have a limited understanding of basic principles governing metabolite use. Increasing access to the essential nutrient iron is one important, but seemingly redundant role performed by both plant and microbial Redox-Active Metabolites (RAMs). We used coumarins, RAMs made by the model plant Arabidopsis thaliana, and phenazines, RAMs made by soil-dwelling pseudomonads, to ask whether plant and microbial RAMs might each have distinct functions under different environmental conditions. We show that variations in oxygen and pH lead to predictable differences in the capacity of coumarins vs phenazines to increase the growth of iron-limited pseudomonads and that these effects depend on whether pseudomonads are grown on glucose, succinate, or pyruvate: carbon sources commonly found in root exudates. Our results are explained by the chemical reactivities of these metabolites and the redox state of phenazines as altered by microbial metabolism. This work shows that variations in the chemical microenvironment can profoundly affect secondary metabolite function and suggests plants may tune the utility of microbial secondary metabolites by altering the carbon released in root exudates. Together, these findings suggest that RAM diversity may be less overwhelming when viewed through a chemical ecological lens: Distinct molecules can be expected to be more or less important to certain ecosystem functions, such as iron acquisition, depending on the local chemical microenvironments in which they reside.

Probing the role of protein conformational changes in the mechanism of prenylated-FMN-dependent phenazine-1-carboxylic acid decarboxylase.

Phenazine-1-carboxylic acid decarboxylase (PhdA) is a prenylated-FMN-dependent (prFMN) enzyme belonging to the UbiD family of decarboxylases. Many UbiD-like enzymes catalyze (de)carboxylation reactions on aromatic rings and conjugated double bonds and are potentially valuable industrial catalysts. We have investigated the mechanism of PhdA using a slow turnover substrate, 2,3-dimethylquinoxaline-5-carboxylic acid (DQCA). Detailed analysis of the pH dependence and solvent deuterium isotope effects associated with the reaction uncovered unusual kinetic behavior. At low substrate concentrations, a substantial inverse solvent isotope effect (SIE) is observed on Vmax/KM of ∼ 0.5 when reaction rates of DQCA in H2O and D2O are compared. Under the same conditions, a normal SIE of 4.15 is measured by internal competition for proton transfer to the product. These apparently contradictory results indicate that the SIE values report on different steps in the mechanism. A proton inventory analysis of the reaction under Vmax/KM and Vmax conditions points to a "medium effect" as the source of the inverse SIE. Molecular dynamics simulations of the effect of D2O on PhdA structure support that D2O reduces the conformational lability of the enzyme and results in a more compact structure, akin to the active, "closed" conformer observed in crystal structures of some UbiD-like enzymes. Consistent with the simulations, PhdA was found to be more stable in D2O and to bind DQCA more tightly, leading to the observed rate enhancement under Vmax/KM conditions.

Phenazine Cations as Anticancer Theranostics†.

The biological properties of two water-soluble organic cations based on polypyridyl structures commonly used as ligands for photoactive transition metal complexes designed to interact with biomolecules are investigated. A cytotoxicity screen employing a small panel of cell lines reveals that both cations show cytotoxicity toward cancer cells but show reduced cytotoxicity to noncancerous HEK293 cells with the more extended system being notably more active. Although it is not a singlet oxygen sensitizer, the more active cation also displayed enhanced potency on irradiation with visible light, making it active at nanomolar concentrations. Using the intrinsic luminescence of the cations, their cellular uptake was investigated in more detail, revealing that the active compound is more readily internalized than its less lipophilic analogue. Colocalization studies with established cell probes reveal that the active cation predominantly localizes within lysosomes and that irradiation leads to the disruption of mitochondrial structure and function. Stimulated emission depletion (STED) nanoscopy and transmission electron microscopy (TEM) imaging reveal that treatment results in distinct lysosomal swelling and extensive cellular vacuolization. Further imaging-based studies confirm that treatment with the active cation induces lysosomal membrane permeabilization, which triggers lysosome-dependent cell-death due to both necrosis and caspase-dependent apoptosis. A preliminary toxicity screen in the Galleria melonella animal model was carried out on both cations and revealed no detectable toxicity up to concentrations of 80 mg/kg. Taken together, these studies indicate that this class of synthetically easy-to-access photoactive compounds offers potential as novel therapeutic leads.

NADH dehydrogenases are the predominant phenazine reductases in the electron transport chain of Pseudomonas aeruginosa.

Phenazines are redox-active secondary metabolites produced by diverse bacteria including the opportunistic pathogen Pseudomonas aeruginosa. Extracellular electron transfer via phenazines enhances anaerobic survival by serving as an electron sink for glucose catabolism. However, the specific phenazine reductase(s) used to support this catabolism are unknown. Because electron transport chain components have been previously implicated in phenazine reduction, we sought to determine which of them possess phenazine reductase activity. We show that phenazine-1-carboxamide (PCN) and pyocyanin (PYO) are reduced at the highest rate by cells and are localized to the cell envelope while reduced. Using a coupled genetic and biochemical approach, we show that phenazine reductase activity in membrane fractions is attributable to the three NADH dehydrogenases present in P. aeruginosa and that their order of phenazine reductase activity is Nqr > Nuo > Ndh. In mutants possessing only one functional NADH dehydrogenase, whole cell reduction rates of PCN, but not PYO, recapitulate the pattern of biochemical results, implying that PYO reduction is predominantly occurring in the cytosol. Lastly, we show that ubiquinone rapidly and non-enzymatically oxidizes reduced phenazines, demonstrating that phenazines have the capability to serve in a redox loop between the NADH and ubiquinone pools, a finding that carries bioenergetic implications.

Quorum-sensing regulation of phenazine production heightens Pseudomonas aeruginosa resistance to ciprofloxacin.

Quorum sensing is a type of cell-cell communication that modulates various biological activities of bacteria. Previous studies indicate that quorum sensing contributes to the evolution of bacterial resistance to antibiotics, but the underlying mechanisms are not fully understood. In this study, we grew Pseudomonas aeruginosa in the presence of sub-lethal concentrations of ciprofloxacin, resulting in a large increase in ciprofloxacin minimal inhibitory concentration. We discovered that quorum sensing-mediated phenazine biosynthesis was significantly enhanced in the resistant isolates, where the quinolone circuit was the predominant contributor to this phenomenon. We found that production of pyocyanin changed carbon flux and showed that the effect can be partially inhibited by the addition of pyruvate to cultures. This study illustrates the role of quorum sensing-mediated phenotypic resistance and suggests a strategy for its prevention.

Phenazine-1 carboxylic acid of Pseudomonas aeruginosa induces the expression of Staphylococcus aureus Tet38 MDR efflux pump and mediates resistance to phenazines and antibiotics.

In this study, we showed that phenazine-1 carboxylic acid (PCA) of Pseudomonas aeruginosa induced the expression of Tet38 efflux pump triggering Staphylococcus aureus resistance to tetracycline and phenazines. Exposure of S. aureus RN6390 to supernatants of P. aeruginosa PA14 and its pyocyanin (PYO)-deficient mutants showed that P. aeruginosa non-PYO phenazines could induce the expression of Tet38 efflux pump. Direct exposure of RN6390 to PCA compound at 0.25× MIC led to a five-fold increase in tet38 transcripts. Expression of Tet38 protein was identified through confocal microscopy using RN6390(pRN-tet38p-yfp) that expressed YFP under control of the tet38 promoter by PCA at 0.25× MIC. The MICs of PCA of a Tet38-overexpressor and a Δtet38 mutant showed a three-fold increase and a two-fold decrease, respectively, compared with that of wild-type. Pre-exposure of RN6390 to PCA (0.25× MIC) for 1 hour prior to addition of tetracycline (1× or 10× MIC) improved bacteria viability of 1.5-fold and 2.6-fold, respectively, but addition of NaCl 7% together with tetracycline at 10× MIC reduced the number of viable PCA-exposed RN6390 of a 2.0-log10 CFU/mL. The transcript levels of tetR21, a repressor of tet38, decreased and increased two-fold in the presence of PCA and NaCl, respectively, suggesting that the effects of PCA and NaCl on tet38 production occurred through TetR21 expression. These data suggest that PCA-induced Tet38 protects S. aureus against tetracycline during coinfection with P. aeruginosa; however, induced tet38-mediated S. aureus resistance to tetracycline is reversed by NaCl 7%, a nebulized treatment used to enhance sputum mobilization in CF patients.

Performance evaluation of machine-assisted interpretation of Gram stains from positive blood cultures.

Manual microscopy of Gram stains from positive blood cultures (PBCs) is crucial for diagnosing bloodstream infections but remains labor intensive, time consuming, and subjective. This study aimed to evaluate a scan and analysis system that combines fully automated digital microscopy with deep convolutional neural networks (CNNs) to assist the interpretation of Gram stains from PBCs for routine laboratory use. The CNN was trained to classify images of Gram stains based on staining and morphology into seven different classes: background/false-positive, Gram-positive cocci in clusters (GPCCL), Gram-positive cocci in pairs (GPCP), Gram-positive cocci in chains (GPCC), rod-shaped bacilli (RSB), yeasts, and polymicrobial specimens. A total of 1,555 Gram-stained slides of PBCs were scanned, pre-classified, and reviewed by medical professionals. The results of assisted Gram stain interpretation were compared to those of manual microscopy and cultural species identification by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The comparison of assisted Gram stain interpretation and manual microscopy yielded positive/negative percent agreement values of 95.8%/98.0% (GPCCL), 87.6%/99.3% (GPCP/GPCC), 97.4%/97.8% (RSB), 83.3%/99.3% (yeasts), and 87.0%/98.5% (negative/false positive). The assisted Gram stain interpretation, when compared to MALDI-TOF MS species identification, also yielded similar results. During the analytical performance study, assisted interpretation showed excellent reproducibility and repeatability. Any microorganism in PBCs should be detectable at the determined limit of detection of 105 CFU/mL. Although the CNN-based interpretation of Gram stains from PBCs is not yet ready for clinical implementation, it has potential for future integration and advancement.

Investigation of the biocontrol mechanism of a novel Pseudomonas species against phytopathogenic Fusarium graminearum revealed by multi-omics integration analysis.

Phytopathogenic Fusarium graminearum poses significant threats to crop health and soil quality. Although our laboratory-cultivated Pseudomonas sp. P13 exhibited potential biocontrol capacities, its effectiveness against F. graminearum and underlying antifungal mechanisms are still unclear. In light of this, our study investigated a significant inhibitory effect of P13 on F. graminearum T1, both in vitro and in a soil environment. Conducting genomic, metabolomic, and transcriptomic analyses of P13, we sought to identify evidence supporting its antagonistic effects on T1. The results revealed the potential of P13, a novel Pseudomonas species, to produce active antifungal components, including phenazine-1-carboxylate (PCA), hydrogen cyanide (HCN), and siderophores [pyoverdine (Pvd) and histicorrugatin (Hcs)], as well as the dynamic adaptive changes in the metabolic pathways of P13 related to these active ingredients. During the logarithmic growth stage, T1-exposed P13 strategically upregulated PCA and HCN biosynthesis, along with transient inhibition of the tricarboxylic acid (TCA) cycle. However, with growth stabilization, upregulation of PCA and HCN synthesis ceased, whereas the TCA cycle was enhanced, increasing siderophores secretion (Pvd and Hcs), suggesting that this mechanism might have caused continuous inhibition of T1. These findings improved our comprehension of the biocontrol mechanisms of P13 and provided the foundation for potential application of Pseudomonas strains in the biocontrol of phytopathogenic F. graminearum. IMPORTANCE: Pseudomonas spp. produces various antifungal substances, making it an effective natural biocontrol agent against pathogenic fungi. However, the inhibitory effects and the associated antagonistic mechanisms of Pseudomonas spp. against Fusarium spp. are unclear. Multi-omics integration analyses of the in vitro antifungal effects of novel Pseudomonas species, P13, against F. graminearum T1 revealed the ability of P13 to produce antifungal components (PCA, HCN, Pvd, and Hcs), strategically upregulate PCA and HCN biosynthesis during logarithmic growth phase, and enhance the TCA cycle during stationary growth phase. These findings improved our understanding of the biocontrol mechanisms of P13 and its potential application against pathogenic fungi.

Phenazine biosynthesis protein MoPhzF regulates appressorium formation and host infection through canonical metabolic and noncanonical signaling function in Magnaporthe oryzae.

Microbe-produced secondary metabolite phenazine-1-carboxylic acid (PCA) facilitates pathogen virulence and defense mechanisms against competitors. Magnaporthe oryzae, a causal agent of the devastating rice blast disease, needs to compete with other phyllosphere microbes and overcome host immunity for successful colonization and infection. However, whether M. oryzae produces PCA or it has any other functions remains unknown. Here, we found that the MoPHZF gene encodes the phenazine biosynthesis protein MoPhzF, synthesizes PCA in M. oryzae, and regulates appressorium formation and host virulence. MoPhzF is likely acquired through an ancient horizontal gene transfer event and has a canonical function in PCA synthesis. In addition, we found that PCA has a role in suppressing the accumulation of host-derived reactive oxygen species (ROS) during infection. Further examination indicated that MoPhzF recruits both the endoplasmic reticulum membrane protein MoEmc2 and the regulator of G-protein signaling MoRgs1 to the plasma membrane (PM) for MoRgs1 phosphorylation, which is a critical regulatory mechanism in appressorium formation and pathogenicity. Collectively, our studies unveiled a canonical function of MoPhzF in PCA synthesis and a noncanonical signaling function in promoting appressorium formation and host infection.

Role of UDP-Glycosyltransferase (ugt) Genes in Detoxification and Glycosylation of 1-Hydroxyphenazine (1-HP) in Caenorhabditis elegans.

Caenorhabditis elegans is a useful model organism to study the xenobiotic detoxification pathways of various natural and synthetic toxins, but the mechanisms of phase II detoxification are understudied. 1-Hydroxyphenazine (1-HP), a toxin produced by the bacterium Pseudomonas aeruginosa, kills C. elegans. We previously showed that C. elegans detoxifies 1-HP by adding one, two, or three glucose molecules in N2 worms. Our current study evaluates the roles that some UDP-glycosyltransferase (ugt) genes play in 1-HP detoxification. We show that ugt-23 and ugt-49 knockout mutants are more sensitive to 1-HP than reference strains N2 or PD1074. Our data also show that ugt-23 knockout mutants produce reduced amounts of the trisaccharide sugars, while the ugt-49 knockout mutants produce reduced amounts of all 1-HP derivatives except for the glucopyranosyl product compared to the reference strains. We characterized the structure of the trisaccharide sugar phenazines made by C. elegans and showed that one of the sugar modifications contains an N-acetylglucosamine (GlcNAc) in place of glucose. This implies broad specificity regarding UGT function and the role of genes other than ogt-1 in adding GlcNAc, at least in small-molecule detoxification.

Improvement of gram staining effect by ethanol pretreatment and quantization of staining image by unsupervised machine learning.

In this study, we propose an Ethanol Pretreatment Gram staining method that significantly enhances the color contrast of the stain, thereby improving the accuracy of judgement, and demonstrated the effectiveness of the modification by eliminating unaided-eye observational errors with unsupervised machine learning image analysis. By comparing the traditional Gram staining method with the improved method on various bacterial samples, results showed that the improved method offers distinct color contrast. Using multimodal assessment strategies, including unaided-eye observation, manual image segmentation, and advanced unsupervised machine learning automatic image segmentation, the practicality of ethanol pretreatment on Gram staining was comprehensively validated. In our quantitative analysis, the application of the CIEDE2000, and CMC color difference standards confirmed the significant effect of the method in enhancing the discrimination of Gram staining.This study not only improved the efficacy of Gram staining, but also provided a more accurate and standardized strategy for analyzing Gram staining results, which might provide an useful analytical tool in microbiological diagnostics.

Dual-mode colorimetric and fluorescence detection of BRCA1 based on a CRISPR-Cas12a system.

Breast cancer, the most common malignant tumor in the world, seriously threatens human life and health. Early diagnosis of breast cancer may help enhance the survival rate. In this work, a colorimetric and fluorescent dual-mode biosensor based on the CRISPR-Cas12a system was constructed to detect the breast cancer biomarker BRCA1. The intact G4 DNA, with the assistance of K+ and hemin, catalyses the oxidation of o-phenylenediamine (OPD) with the assistance of hydrogen peroxide (H2O2), generating the oxidation product 2,3-diaminophenazine (DAP), which has distinct absorption and fluorescence peaks. The presence of the target BRCA1 activates the trans-cleavage activity of CRISPR-Cas12a, leading to the cleavage of G4 DNA and inhibiting the catalytic oxidation of OPD. Target BRCA1 was quantitatively determined by measuring both the absorbance and fluorescence intensity of DAP. The detection limits were calculated to be 0.615 nM for the colorimetric method and 0.289 nM for the fluorescence method. The dual-mode biosensor showed good selectivity and reliability for BRCA1 and can resist interference from complex substrates, and it has great potential in biomedical detection.

Dihydrophenazine: a multifunctional new weapon that kills multidrug-resistant Acinetobacter baumannii and restores carbapenem and oxidative stress susceptibilities.

AIMS: The current work aims to fully characterize a new antimicrobial agent against Acinetobacter baumannii, which continues to represent a growing threat to healthcare settings worldwide. With minimal treatment options due to the extensive spread of resistance to almost all the available antimicrobials, the hunt for new antimicrobial agents is a high priority. METHODS AND RESULTS: An Egyptian soil-derived bacterium strain NHM-077B proved to be a promising source for a new antimicrobial agent. Bio-guided fractionation of the culture supernatants of NHM-077B followed by chemical structure elucidation identified the active antimicrobial agent as 1-hydroxy phenazine. Chemical synthesis yielded more derivatives, including dihydrophenazine (DHP), which proved to be the most potent against A. baumannii, yet it exhibited a marginally safe cytotoxicity profile against human skin fibroblasts. Proteomics analysis of the cells treated with DHP revealed multiple proteins with altered expression that could be correlated to the observed phenotypes and potential mechanism of the antimicrobial action of DHP. DHP is a multipronged agent that affects membrane integrity, increases susceptibility to oxidative stress, interferes with amino acids/protein synthesis, and modulates virulence-related proteins. Interestingly, DHP in subinhibitory concentrations re-sensitizes the highly virulent carbapenem-resistant A. baumannii strain AB5075 to carbapenems providing great hope in regaining some of the benefits of this important class of antibiotics. CONCLUSIONS: This work underscores the potential of DHP as a promising new agent with multifunctional roles as both a classical and nonconventional antimicrobial agent that is urgently needed.

Tepuazines A-E: Phenazine Glycosides from a Venezuelan Quartz-Rich (Tepui) Cave Soil-Derived Streptomyces virginiae CMB-CA091.

Investigation of the secondary metabolites of Streptomyces virginiae CMB-CA091 isolated from the quartz-rich (tepui) soil of a cave in Venezuela yielded two new dimeric phenazine glycosides, tepuazines A and B (1 and 2); three new monomeric phenazine glycosides, tepuazines C-E (3-5); and a series of known analogues, baraphenazine G (6), phenazinolin D (7), izumiphenazine C (8), 4-methylaminobenzoyl-l-rhamnopyranoside (9), and 2-acetamidophenol (10). Structures were assigned to 1-10 on the basis of detailed spectroscopic analysis and biosynthetic considerations, with 1 and 2 featuring a rare 2-oxabicyclo[3.3.1]nonane-like ring C/D bridge shared with only a handful of known Streptomyces natural products. We propose a plausible convergent biosynthetic relationship linking all known members of this structure class that provides a rationale for the observed ring C/D configuration.

Elucidation of the Biosynthesis of Griseoluteic Acid in Streptomyces griseoluteus P510.

Phenazines are aromatic compounds with antifungal and cytotoxic activities. Phenazines incorporating phenazine 1-carboxylic acid have widespread applications in agriculture, medicine, and industry. Griseoluteic acid is a cytotoxic compound secreted by Streptomyces griseoluteus P510, displaying potential medical applications. However, the biosynthetic pathway of griseoluteic acid has not been elucidated, limiting its development and application. In this study, a conserved phenazine biosynthetic gene cluster of S. griseoluteus P510 was identified through genomic analysis. Subsequently, its was confirmed that the four essential modification enzymes SgpH, SgpI, SgpK, and SgpL convert phenazine-1,6-dicarboxylic acid into griseoluteic acid by heterologous expression in Escherichia coli. Moreover, the biosynthetic pathway of griseoluteic acid was established in Pseudomonas chlororaphis characterized by a high growth rate and synthesis efficiency of phenazines, laying the foundation for the efficient production of griseoluteic acid.