Isolation and identification of bioactive substance 1-hydroxyphenazine from Pseudomonas aeruginosa and its antimicrobial activity

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.

Viruses of plant-pathogenic fungi: a promising biocontrol strategy for Sclerotinia sclerotiorum

Plant pathogenic fungi pose a significant and ongoing threat to agriculture and food security, causing economic losses and significantly reducing crop yields. Effectively managing these fungal diseases is crucial for sustaining agricultural productivity, and in this context, mycoviruses have emerged as a promising biocontrol option. These viruses alter the physiology of their fungal hosts and their interactions with the host plants. This review encompasses the extensive diversity of reported mycoviruses, including their taxonomic classification and range of fungal hosts. We highlight representative examples of mycoviruses that affect economically significant plant-pathogenic fungi and their distinctive characteristics, with a particular emphasis on mycoviruses impacting Sclerotinia sclerotiorum. These mycoviruses exhibit significant potential for biocontrol, supported by their specificity, efficacy, and environmental safety. This positions mycoviruses as valuable tools in crop protection against diseases caused by this pathogen, maintaining their study and application as promising research areas in agricultural biotechnology. The remarkable diversity of mycoviruses, coupled with their ability to infect a broad range of plant-pathogenic fungi, inspires optimism, and suggests that these viruses have the potential to serve as an effective management strategy against major fungi-causing plant diseases worldwide.

Upcycling of food waste streams to valuable biopigments pyocyanin and 1-hydroxyphenazine

Phenazines, including pyocyanin (PYO) and 1-hydroxyphenazine (1-HP) are extracellular secondary metabolites and multifunctional pigments of Pseudomonas aeruginosa responsible for its blue-green color. These versatile molecules are electrochemically active, involved in significant biological activities giving fitness to the host, but also recognized as antimicrobial and anticancer agents. Their wider application is still limited partly due to the cost of carbon substrate for production, which can be solved by the utilization of carbon from food waste within the biorefinery concept. In this study, a variety of food waste streams (banana peel, potato peel, potato washing, stale bread, yoghurt, processed meat, boiled eggs and mixed canteen waste) was used as sole nutrient source in submerged cultures of P. aeruginosa BK25H. Stale bread was identified as the most suitable substrate to support phenazine biopigments production and bacterial growth. This was further increased in 5-liter fermenter when on average 5.2 mg L-1 of PYO and 4.4 mg L-1 of 1-HP were purified after 24 h batch cultivations from the fermentation medium consisting of homogenized stale bread in tap water. Purified biopigments showed moderate antimicrobial activity, and showed different toxicity profiles, with PYO not being toxic against Caenorhabditis elegans, a free-living soil nematode up to 300 µg mL-1 and 1-HP showing lethal effects at 75 µg mL-1. Therefore, stale bread waste stream with minimal pretreatment should be considered as suitable biorefinery feedstock, as it can support the production of valuable biopigments such as phenazines.

Plant Protection Mediated Through an Array of Metabolites Produced by Pantoea dispersa Isolated from Pitcher Plant

In the study, the bacterial isolate NhPB54 purified from the pitcher of Nepenthes plant was observed to have activity against Pythium aphanidermatum by dual culture and well diffusion. Hence, it was subjected to 16S rDNA sequencing and BLAST analysis, where the NhPB54 was found to have 100% identity to Pantoea dispersa. Upon screening for the plant beneficial properties, Pantoea dispersa NhPB54 was found to be positive for phosphate, potassium and zinc solubilization, nitrogen fixation, indole-3-acetic acid, ammonia, 1-aminocyclopropane-1-carboxylate deaminase, biofilm and biosurfactant production. Further to this, Solanum lycopersicum seedlings primed with P. dispersa NhPB54 were studied for the improved plant growth and disease protection. Here, the seedlings pre-treated with the NhPB54 culture supernatant were found to have enhanced plant growth and protection from damping off and fruit rot caused by P. aphanidermatum. From the LC-QTOF-MS/MS and GC MS analysis, P. dispersa NhPB54 was found to produce a blend of chemicals including 1-hydroxyphenazine, surfactin, and other bioactive metabolites with the likely basis of its observed antifungal and plant growth-promoting properties. From the results of the study, plants with unique adaptations can expect to harbor microbial candidates with beneficial applications.

Recent Developments in the Biological Activities, Bioproduction, and Applications of Pseudomonas spp. Phenazines

Phenazines are a large group of heterocyclic nitrogen-containing compounds with demonstrated insecticidal, antimicrobial, antiparasitic, and anticancer activities. These natural compounds are synthesized by several microorganisms originating from diverse habitats, including marine and terrestrial sources. The most well-studied producers belong to the Pseudomonas genus, which has been extensively investigated over the years for its ability to synthesize phenazines. This review is focused on the research performed on pseudomonads' phenazines in recent years. Their biosynthetic pathways, mechanism of regulation, production processes, bioactivities, and applications are revised in this manuscript.

Utilization of Fishery-Processing By-Product Squid Pens for Scale-Up Production of Phenazines via Microbial Conversion and Its Novel Potential Antinematode Effect

Fishery by-products (FBPs) have been increasingly investigated for the extraction and production of a vast array of active molecules. The aim of this study was to produce phenazine compounds from FBPs via microbial fermentation and assess their novel antinematode effect. Among various FBPs, squid pen powder (SPP) was discovered as the most suitable substrate for phenazine production by Pseudomonas aeruginosa TUN03 fermentation. Various small-scale experiments conducted in flasks for phenazine production indicated that the most suitable was the newly designed liquid medium which included 1% SPP, 0.05% MgSO4, and 0.1% Ca3(PO4)2 (initial pH 7). Phenazines were further studied for scale-up bioproduction in a 14 L bioreactor system resulting in a high yield (22.73 µg/mL) in a much shorter cultivation time (12 h). In the fermented culture broth, hemi-pyocyanin (HPC) was detected as a major phenazine compound with an area percentage of 11.28% in the crude sample. In the bioactivity tests, crude phenazines and HPC demonstrate novel potential nematicidal activity against black pepper nematodes, inhibiting both juveniles (J2) nematodes and egg hatching. The results of this work suggest a novel use of SPP for cost-effective bioproduction of HPC, a novel potential nematodes inhibitor. Moreover, the combination of MgSO4 and Ca3(PO4)2 was also found to be a novel salt composition that significantly enhanced phenazine yield by P. aeruginosa fermentation in this work.

Novel α-Amylase Inhibitor Hemi-Pyocyanin Produced by Microbial Conversion of Chitinous Discards

α-Amylase inhibitors (aAIs) have been applied for the efficient management of type 2 diabetes. The aim of this study was to search for potential aAIs produced by microbial fermentation. Among various bacterial strains, Pseudomonas aeruginosa TUN03 was found to be a potential aAI-producing strain, and shrimp heads powder (SHP) was screened as the most suitable C/N source for fermentation. P. aeruginosa TUN03 exhibited the highest aAIs productivity (3100 U/mL) in the medium containing 1.5% SHP with an initial pH of 7–7.5, and fermentation was performed at 27.5 °C for two days. Further, aAI compounds were investigated for scaled-up production in a 14 L-bioreactor system. The results revealed a high yield (4200 U/mL) in a much shorter fermentation time (12 h) compared to fermentation in flasks. Bioactivity-guided purification resulted in the isolation of one major target compound, identified as hemi-pyocyanin (HPC) via gas chromatography-mass spectrometry and nuclear magnetic resonance. Its purity was analyzed by high-performance liquid chromatography. HPC demonstrated potent α-amylase inhibitory activity comparable to that of acarbose, a commercial antidiabetic drug. Notably, HPC was determined as a new aAI. The docking study indicated that HPC inhibits α-amylase by binding to amino acid Arg421 at the biding site on enzyme α-amylase with good binding energy (−9.3 kcal/mol) and creating two linkages of H-acceptors.

Pseudomonas fluorescens Showing Antifungal Activity against Macrophomina phaseolina, a Severe Pathogenic Fungus of Soybean, Produces Phenazine as the Main Active Metabolite

Pseudomonas fluorescens 9 and Bacillus subtilis 54, proposed as biofungicides to control Macrophomina phaseolina, a dangerous pathogen of soybean and other crops, were grown in vitro to evaluate their ability to produce metabolites with antifungal activity. The aim of the manuscript was to identify the natural compounds responsible for their antifungal activity. Only the culture filtrates of P. fluorescens 9 showed strong antifungal activity against M. phaseolina. Its organic extract contained phenazine and mesaconic acid (1 and 2), whose antifungal activity was tested against M. phaseolina, as well as Cercospora nicotianae and Colletotrichum truncatum, other pathogens of soybean; however, only compound 1 exhibited activity. The antifungal activity of compound 1 was compared to phenazine-1-carboxylic acid (PCA, 3), 2-hydroxyphenazine (2-OH P, 4), and various semisynthetic phenazine nitro derivatives in order to perform a structure-activity relationship (SAR) study. PCA and phenazine exhibited the same percentage of growth inhibition in M. phaseolina and C. truncatum, whereas PCA (3) showed lower activity against C. nicotianae than phenazine. 2-Hydroxyphenazine (4) showed no antifungal activity against M. phaseolina. The results of the SAR study showed that electron attractor (COOH and NO2) or repulsor (OH) groups significantly affect the antifungal growth, as well as their α- or β-location on the phenazine ring. Both PCA and phenazine could be proposed as biopesticides to control the soybean pathogens M. phaseolina, C. nicotianae, and C. truncatum, and these results should prompt an investigation of their large-scale production and their suitable formulation for greenhouse and field applications.

In Vitro Study of Biocontrol Potential of Rhizospheric Pseudomonas aeruginosa against Pathogenic Fungi of Saffron (Crocus sativus L.)

Plant rhizosphere soil contains a large number of plant-growth promoting rhizobacteria, which can not only resist the invasion of pathogenic microorganisms and protect plants from damage, but also promote the growth and development of plants. In this study, Pseudomonas aeruginosa strain YY322, isolated and screened from the rhizosphere soil of saffron (Crocus sativus L.), was found through a plate confrontation experiment to show highly effectual and obvious antagonistic activity against the pathogens of saffron, including Fusarium oxysporum, Fusarium solani, Penicillium citreosulfuratum, Penicillium citrinum and Stromatinia gladioli. In addition, the volatile organic compounds of strain YY322 had great antagonistic activity against these pathogens. Observation under a scanning electron microscope and transmission electron microscope reflected that strain YY322 had a significant effect on the hyphae and conidia of F. oxysporum and F. solani. Through the detection of degrading enzymes, it was found that P. aeruginosa can secrete protease and glucanase. The plant growth promoting performance was evaluated, finding that strain YY322 had the functions of dissolving phosphorus, fixing nitrogen, producing siderophore and producing NH3. In addition, whole genome sequencing analysis indicated that the YY322 genome is comprised of a 6,382,345-bp circular chromosome, containing 5809 protein-coding genes and 151 RNA genes. The P. aeruginosa YY322 genome encodes genes related to phenazine (phzABDEFGIMRS), hydrogen cyanide(HCN) (hcnABC), surfactin (srfAA), salicylate (pchA), biofilm formation (flgBCDEFGHIJKL, motAB, efp, hfq), and colonization (minCDE, yjbB, lysC). These results collectively indicated the role of P. aeruginosa YY322 in plant growth enhancement and biocontrol mechanisms. All in all, this study provides a theoretical basis for P. aeruginosa as the PGPR of saffron, paving the way for the subsequent development and utilization of microbial fertilizer.

Anti-Inflammatory Effects of an Extract from Pseudomonas aeruginosa and Its Purified Product 1-Hydroxyphenazine on RAW264.7 Cells

The purpose of this study was to discuss the effects of an extract from the culture medium of Pseudomonas aeruginosa (P. aeruginosa) 2016NX1 (chloroform extract of P. aeruginosa, CEPA) and its purified product 1-hydroxyphenazine on RAW264.7 cell inflammation. Cell viability was evaluated by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) method. TNF-α production was determined by an ELISA method. The effects of CEPA and its purified product 1-hydroxyphenazine on cell morphology were investigated using an inverted microscope. Quantitative real-time PCR was performed to determine mRNA expression levels. CEPA and 1-hydroxyphenazine had no obvious toxicity to cells when their concentrations were no more than 20 μg ml^-1 and 5 μg ml^-1, respectively. Both CEPA and 1-hydroxyphenazine suppressed the secretion of TNF-α and significantly reduced the mRNA expression levels of TNF-α, IL-1β, and IL-6. Both CEPA and 1-hydroxyphenazine inhibited M1 cell polarization after lipopolysaccharide (LPS) stimulation. The results in this article lay a good foundation for the biopharmaceutical applications of CEPA and 1-hydroxyphenazine in the future. CEPA and 1-hydroxyphenazine had certain anti-inflammatory activity, and inhibited LPS-induced RAW264.7 cell inflammation. Our findings suggest that CEPA and 1-hydroxyphenazine are potential chemicals with anti-inflammatory activity.

Cloning and Characterization of phzR Gene from Pseudomonas aeruginosa

A gene encoding phzR was isolated from a phenazine-producing bacterium Pseudomonas aeruginosa 2016NX1. This paper provided the full-length cDNA encoding phzR (GenBank Accession no., MW143078). The cDNA of the phzR contained an open reading frame (ORF) of 714 bp. The potential regulatory elements were predicted in the phzR promoter region. The deduced amino acid sequence of P. aeruginosa phzR showed significant homology to the known phzRs from different organisms. Gene overexpression analysis showed that the phenazine content was improved (44.39%) in comparison to wild-type 2016NX1.

Isolation and Characterization of Pseudomonas sp. Cr13 and Its Application in Removal of Heavy Metal Chromium

The purpose of this study was to elaborate the characteristics of Pseudomonas sp. Cr13, including physiological and biochemical characteristics, optimization of growth conditions, minimum inhibitory concentration of Cr⁶⁺ and resistance to other heavy metals, removal efficiency of Cr⁶⁺, and antibiotics sensitivity. A strain Pseudomonas sp. Cr13 was screened from mine-contaminated soils, which could tolerate high concentration of Cr⁶⁺ (up to 250 mg l^-1) and Cd²⁺ (50 mg l^-1). The optimum pH, NaCl concentration, and temperature for growth were 6, 10% NaCl, and 30 °C, respectively. The removal efficiency of Cr⁶⁺ by strain Pseudomonas sp. Cr13 was studied. The removal efficiency of Cr⁶⁺ decreased with the increased concentration of Cr⁶⁺. Under the optimal conditions, the maximum of the removal rate can reach up to 94.26% in contaminated soils. In addition, antibiotics sensitivity of this strain was investigated. It was found that this strain was sensitive to nine types of antibiotics, which would lay a good foundation for the choice of selective marker in genetic engineering modification of this strain. The results in this article would lay a good foundation for the bioremediation of heavy metals pollution in the future. Pseudomonas sp. Cr13 can tolerate high concentration of Cr⁶⁺ and partially remove Cr⁶⁺, which make Cr13 an attractive option for the bioremediation of heavy metal chromium (Cr). Our findings suggest that Pseudomonas sp. Cr13 is a potential bacterium with the ability of bioremediation of heavy metal Cr.