Genomic analysis and temperature-dependent transcriptome profiles of the rhizosphere originating strain Pseudomonas aeruginosa M18

Isolation and Characterization of Potassium-Solubilizing Rhizobacteria (KSR) Promoting Cotton Growth in Saline-Sodic Regions

Cotton is highly sensitive to potassium, and Xinjiang, China's leading cotton-producing region, faces a severe challenge due to reduced soil potassium availability. Biofertilizers, particularly potassium-solubilizing rhizobacteria (KSR), convert insoluble potassium into plant-usable forms, offering a sustainable solution for evergreen agriculture. This study isolated and characterized KSR from cotton, elucidated their potassium solubilization mechanisms, and evaluated the effects of inoculating KSR strains on cotton seedlings. Twenty-three KSR strains were isolated from cotton rhizosphere soil using modified Aleksandrov medium. Their solubilizing capacities were assessed in a liquid medium. Strain A10 exhibited the highest potassium solubilization capacity (21.8 ppm) by secreting organic acids such as lactic, citric, acetic, and succinic acid, lowering the pH and facilitating potassium release. A growth curve analysis and potassium solubilization tests of A10 under alkali stress showed its vigorous growth and maintained solubilization ability at pH 8-9, with significant inhibition at pH 10. Furthermore, 16S rRNA sequencing identified strain A10 as Pseudomonas aeruginosa. Greenhouse pot experiments showed that inoculating cotton plants with strain A10 significantly increased plant height and promoted root growth. This inoculation also enhanced dry biomass accumulation in both the aerial parts and root systems of the plants, while reducing the root-shoot ratio. These results suggest that Pseudomonas aeruginosa A10 has potential as a biofertilizer, offering a new strategy for sustainable agriculture.

Genomics Analysis Reveals the Potential Biocontrol Mechanism of Pseudomonas aeruginosa QY43 against Fusarium pseudograminearum

Fusarium crown rot (FCR) in wheat is a prevalent soil-borne disease worldwide and poses a significant threat to the production of wheat (Triticum aestivum) in China, with F. pseudograminearum being the dominant pathogen. Currently, there is a shortage of biocontrol resources to control FCR induced by F. pseudograminearum, along with biocontrol mechanisms. In this study, we have identified 37 strains of biocontrol bacteria displaying antagonistic effects against F. pseudograminearum from over 8000 single colonies isolated from soil samples with a high incidence of FCR. Among them, QY43 exhibited remarkable efficacy in controlling FCR. Further analysis identified the isolate QY43 as Pseudomonas aeruginosa, based on its colony morphology and molecular biology. In vitro, QY43 significantly inhibited the growth, conidial germination, and the pathogenicity of F. pseudograminearum. In addition, QY43 exhibited a broad spectrum of antagonistic activities against several plant pathogens. The genomics analysis revealed that there are genes encoding potential biocontrol factors in the genome of QY43. The experimental results confirmed that QY43 secretes biocontrol factor siderophores and pyocyanin. In summary, QY43 exhibits a broad spectrum of antagonistic activities and the capacity to produce diverse biocontrol factors, thereby showing substantial potential for biocontrol applications to plant disease.

Enhancing Botrytis disease management in tomato plants: insights from a Pseudomonas putida strain with biocontrol activity

AIMS

This study explores the biocontrol potential of Pseudomonas putida Z13 against Botrytis cinerea in tomato plants, addressing challenges posed by the pathogen's fungicide resistance. The aims of the study were to investigate the in vitro and in silico biocontrol traits of Z13, identify its plant-colonizing efficacy, evaluate the efficacy of different application strategies against B. cinerea in planta, and assess the capacity of Z13 to trigger induced systemic resistance (ISR) in plants.

METHODS AND RESULTS

The in vitro experiments revealed that Z13 inhibits the growth of B. cinerea, produces siderophores, and exhibits swimming and swarming activity. Additionally, the Z13 genome harbors genes that encode compounds triggering ISR, such as pyoverdine and pyrroloquinoline quinone. The in planta experiments demonstrated Z13's efficacy in effectively colonizing the rhizosphere and leaves of tomato plants. Therefore, three application strategies of Z13 were evaluated against B. cinerea: root drenching, foliar spray, and the combination of root drenching and foliar spray. It was demonstrated that the most effective treatment of Z13 against B. cinerea was the combination of root drenching and foliar spray. Transcriptomic analysis showed that Z13 upregulates the expression of the plant defense-related genes PR1 and PIN2 upon B. cinerea inoculation.

CONCLUSION

The results of the study demonstrated that Z13 possesses significant biocontrol traits, such as the production of siderophores, resulting in significant plant protection against B. cinerea when applied as a single treatment to the rhizosphere or in combination with leaf spraying. Additionally, it was shown that Z13 root colonization primes plant defenses against the pathogen.

Diversity and antibacterial activity of endophytic bacteria associated with medicinal plant, Scrophularia striata

To search endophytic bacteria diversity and evaluate their antibacterial activity, healthy medicinal plant of Scrophularia striata was chosen in this study. One hundred endophytic bacteria were isolated from surface-sterilized tissues (root, stem and leaf) of S. striata. Using sequence analysis targeting 16S rRNA gene, eight genera, including Agrococcus, Arthrobacter, Bacillus, Chryseobacterium, Delftia, Kocuria, Pseudomonas and Sphingomonas were identified. Antibacterial activity of endophytic bacteria was examined against some test bacteria, employing agar well diffusion method. Out of 31 endophytic bacterial isolates, 24(77.42%) isolates showed significant antimicrobial activity against Bacillus cereus, 17(54.84%) isolates exhibited maximum activity against Staphylococcus aureus, 14(45.16%) isolates against Escherichia coli and 5(16.13%) isolates showed positive activity against Proteus mirabilis.The results obtained in this study suggested that the medicinal plant, S. striatais is a potent source of endophytic bacteria with antibacterial activity and offers promise for discovery of more impressive biological compounds.

The Lon protease negatively regulates pyoluteorin biosynthesis through the Gac/Rsm-RsmE cascade and directly degrades the transcriptional activator PltR in Pseudomonas protegens H78

Pyoluteorin (Plt) is a broad-spectrum antibiotic with antibacterial and antifungal activities. In Pseudomonas protegens H78, the Plt biosynthetic operon pltLABCDEFG is transcriptionally activated by the LysR-type regulator PltR and is positively regulated by the Gac/Rsm signal transduction cascade (GacS/A-RsmXYZ-RsmE-pltR/pltAB). Additionally, Plt biosynthesis has been shown to be significantly enhanced by mutation of the Lon protease-encoding gene. This study aims to understand the negative regulation pathway and molecular mechanism by which Lon functions in Plt biosynthesis. lon deletion was first found to improve the antimicrobial ability of strain H78 due to its increased Plt production, while partially inhibiting the growth of H78 strain. Lon protease decreases the abundance and stability of the two-component system response regulator GacA and thus participates in the abovementioned Gac/Rsm cascade and negatively regulates Plt biosynthesis. Similarly, Lon protease also decreases the abundance and stability of transcriptional activator PltR. PltR protein can be directly degraded by the Lon protease but not by a mutated form of Lon protease with an amino acid replacement of S₆₇₄ -A. In summary, Lon protease negatively regulates Plt biosynthesis via both the Gac/Rsm-mediated global regulatory pathway and the direct degradation of the transcriptional activator PltR in P. protegens H78.

Plant Growth-Promoting Activity of Pseudomonas aeruginosa FG106 and Its Ability to Act as a Biocontrol Agent against Potato, Tomato and Taro Pathogens

P. aeruginosa strain FG106 was isolated from the rhizosphere of tomato plants and identified through morphological analysis, 16S rRNA gene sequencing, and whole-genome sequencing. In vitro and in vivo experiments demonstrated that this strain could control several pathogens on tomato, potato, taro, and strawberry. Volatile and non-volatile metabolites produced by the strain are known to adversely affect the tested pathogens. FG106 showed clear antagonism against Alternaria alternata, Botrytis cinerea, Clavibacter michiganensis subsp. michiganensis, Phytophthora colocasiae, P. infestans, Rhizoctonia solani, and Xanthomonas euvesicatoria pv. perforans. FG106 produced proteases and lipases while also inducing high phosphate solubilization, producing siderophores, ammonia, indole acetic acid (IAA), and hydrogen cyanide (HCN) and forming biofilms that promote plant growth and facilitate biocontrol. Genome mining approaches showed that this strain harbors genes related to biocontrol and growth promotion. These results suggest that this bacterial strain provides good protection against pathogens of several agriculturally important plants via direct and indirect modes of action and could thus be a valuable bio-control agent.

A Biocontrol Strain of Pseudomonas aeruginosa CQ-40 Promote Growth and Control Botrytis cinerea in Tomato

Botrytis cinerea infection can be very devastating for tomato production, as it can result in a large-scale reduction in tomato fruit production and fruit quality after harvest. Thus, it negatively affects tomato yield and quality. In this study, a biocontrol bacteria CQ-4 was isolated and screened from the rhizosphere soil of tomato plants. Morphological, physiological, and biochemical characteristics and 16S rDNA sequence analysis revealed that it belongs to the species Pseudomonas aeruginosa, which has a strong antagonistic effect against Botrytis cinerea. In addition, the bacterium's antibacterial spectrum is relatively extensive, and antagonistic tests have shown that it also has varying degrees of inhibition on other 12 plant diseases. The growth promotion test showed that the strain has a clear promotion effect on tomato seed germination and seedling growth. The growth-promoting effect on plant height, stem thickness, dry and fresh weight and main root length of tomato seedlings was significantly improved after the seeds were soaked in a bacterial solution of 2.5 × 108 cfu mL-1 concentration. This did not only maintain the nutritional quality of tomato fruits, but also prevents them from rotting. In vitro and pot experiments showed that the strain CQ-4 can effectively control tomato gray mold, and the control effects on tomato leaves and fruits reached 74.4% and 66.0%, respectively. Strain CQ-4 induce plants to up-regulate the activities of four disease-resistant defense enzymes. The peak enzymatic activities of Phenylalanine Ammonia Lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD), and Superoxide Dismutase (SOD) were increased by 35.6%, 37.6%, 46.1%, and 38.4%, respectively, as compared with the control group. This study found that the strain can solubilize phosphorus, fix nitrogen, and produce cellulase, protease, ferrophilin, and other antibacterial metabolites, but it does not produce chitinase, glucanase, and HCN (hydrocyanic acid). This research screened out an excellent Pseudomonas aeruginosa strain that can stably and effectively control tomato gray mold, and it provided theoretical basis for further development and the application of biological agents.

Genomic Features of a Food-Derived Pseudomonas aeruginosa Strain PAEM and Biofilm-Associated Gene Expression under a Marine Bacterial α-Galactosidase

The biofilm-producing strains of P. aeruginosa colonize various surfaces, including food products and industry equipment that can cause serious human and animal health problems. The biofilms enable microorganisms to evolve the resistance to antibiotics and disinfectants. Analysis of the P. aeruginosa strain (serotype O6, sequence type 2502), isolated from an environment of meat processing (PAEM) during a ready-to-cook product storage (−20 °C), showed both the mosaic similarity and differences between free-living and clinical strains by their coding DNA sequences. Therefore, a cold shock protein (CspA) has been suggested for consideration of the evolution probability of the cold-adapted P. aeruginosa strains. In addition, the study of the action of cold-active enzymes from marine bacteria against the food-derived pathogen could contribute to the methods for controlling P. aeruginosa biofilms. The genes responsible for bacterial biofilm regulation are predominantly controlled by quorum sensing, and they directly or indirectly participate in the synthesis of extracellular polysaccharides, which are the main element of the intercellular matrix. The levels of expression for 14 biofilm-associated genes of the food-derived P. aeruginosa strain PAEM in the presence of different concentrations of the glycoside hydrolase of family 36, α-galactosidase α-PsGal, from the marine bacterium Pseudoalteromonas sp. KMM 701 were determined. The real-time PCR data clustered these genes into five groups according to the pattern of positive or negative regulation of their expression in response to the action of α-galactosidase. The results revealed a dose-dependent mechanism of the enzymatic effect on the PAEM biofilm synthesis and dispersal genes.

Identification of a Strong Quorum Sensing- and Thermo-Regulated Promoter for the Biosynthesis of a New Metabolite Pesticide Phenazine-1-carboxamide in Pseudomonas strain PA1201

Phenazine-1-carboxamide (PCN) produced by multifarious Pseudomonas strains represents a promising candidate as a new metabolite pesticide due to its broad-spectrum antifungal activity and capacity to induce systemic resistance in plants. The rice rhizosphere Pseudomonas strain PA1201 contains two reiterated gene clusters, phz1 and phz2, for phenazine-1-carboxylic acid (PCA) biosynthesis; PCA is further converted into PCN by this strain using a functional phzH-encoding glutamine aminotransferase. However, PCN levels in PA1201 constitute approximately one-fifth of PCA levels and the optimal temperature for PCN synthesis is 28 °C. In this study, the phzH open reading frame (ORF) and promoter region were investigated and reannotated. phzH promoter P_phzH was found to be a weak promoter, and PhzH levels were not sufficient to convert all of the native PCA into PCN. Following RNA Seq and promoter-lacZ fusion analyses, a strong quorum sensing (QS)- and thermo-regulated promoter P_rhlI was identified and characterized. The activity of P_phzH is approximately 1% of P_rhlI in PA1201. After three rounds of promoter editing and swapping by P_rhlI, a new PCN-overproducing strain UP46 was generated. The optimal fermentation temperature for PCN biosynthesis in UP46 was increased from 28 to 37 °C and the PCN fermentation titer increased 179.5-fold, reaching 14.1 g/L, the highest ever reported.

Genome analysis of plant growth-promoting rhizobacterium Pseudomonas chlororaphis subsp. aurantiaca JD37 and insights from comparasion of genomics with three Pseudomonas strains

Pseudomonas chlororaphis subsp. aurantiaca strain JD37 is a plant growth-promoting rhizobacterium (PGPR), which has important biotechnological features such as plant growth promotion, rhizosphere colonization and biocontrol activities. In present study, the genome sequence of JD37 was obtained and comparative genomic analysis were performed to explore unique features of the JD37 genome and its relationship with other Pseudomonas PGPR: P. chlororaphis PA23, P. protegens Pf-5 and P. aeruginosa M18. JD37 possessed a single circular chromosome of 6,702,062 bp in length with an average GC content of 62.75 %. No plasmid was detected in JD37. A total of 5003 functional proteins of JD37 were predicted according to the clusters of orthologous groups (COGs) database. The JD37 genome consisted of various genes involved in plant growth promotion, biocontrol activities and defense responses. Genes involved in the rhizosphere colonization and motility were also found in the genome of JD37, suggesting the common plant growth-promoting traits in PGPR. The identified resistance genes (e.g. those related to metal resistance, antibiotics, and osmotic and temperature-shock) and secondary metabolite biosynthesis revealed the pathways for metabolites it produced. Data presented in present study further provided valuable information on its molecular genetics and adaptive capacity in the rhizosphere niche.

The (p)ppGpp-mediated stringent response regulatory system globally inhibits primary metabolism and activates secondary metabolism in Pseudomonas protegens H78

Pseudomonas protegens H78 produces multiple secondary metabolites, including antibiotics and iron carriers. The guanosine pentaphosphate or tetraphosphate ((p)ppGpp)-mediated stringent response is utilized by bacteria to survive during nutritional starvation and other stresses. RelA/SpoT homologues are responsible for the biosynthesis and degradation of the alarmone (p)ppGpp. Here, we investigated the global effect of relA/spoT dual deletion on the transcriptomic profiles, physiology, and metabolism of P. protegens H78 grown to mid- to late log phase. Transcriptomic profiling revealed that relA/spoT deletion globally upregulated the expression of genes involved in DNA replication, transcription, and translation; amino acid metabolism; carbohydrate and energy metabolism; ion transport and metabolism; and secretion systems. Bacterial growth was partially increased, while the cell survival rate was significantly reduced by relA/spoT deletion in H78. The utilization of some nutritional elements (C, P, S, and N) was downregulated due to relA/spoT deletion. In contrast, relA/spoT mutation globally inhibited the expression of secondary metabolic gene clusters (plt, phl, prn, ofa, fit, pch, pvd, and has). Correspondingly, antibiotic and iron carrier biosynthesis, iron utilization, and antibiotic resistance were significantly downregulated by the relA/spoT mutation. This work highlights that the (p)ppGpp-mediated stringent response regulatory system plays an important role in inhibiting primary metabolism and activating secondary metabolism in P. protegens.

Antimicrobial secondary metabolites from agriculturally important bacteria as next-generation pesticides

The whole organisms can be packaged as biopesticides, but secondary metabolites secreted by microorganisms can also have a wide range of biological activities that either protect the plant against pests and pathogens or act as plant growth promotors which can be beneficial for the agricultural crops. In this review, we have compiled information about the most important secondary metabolites of three important bacterial genera currently used in agriculture pest and disease management.

Coenzyme Q biosynthesis in the biopesticide Shenqinmycin-producing Pseudomonas aeruginosa strain M18

Coenzyme Q (ubiquinone) is a redox-active isoprenylated benzoquinone commonly found in living organisms. The biosynthetic pathway for this lipid has been extensively studied in Escherichia coli and Saccharomyces cerevisiae; however, little is known in Pseudomonas aeruginosa. In this study, we observed that CoQ9 is the predominant coenzyme Q synthesized by the Shenqinmycin-producing strain M18. BLASTP and domain organization analyses identified 15 putative genes for CoQ biosynthesis in M18. The roles of 5 of these genes were genetically and biochemically investigated. PAM18_4662 encodes a nonaprenyl diphosphate synthase (Nds) and determines the number of isoprenoid units of CoQ9 in M18. PAM18_0636 (coq7PA) and PAM18_5179 (ubiJPA) are essential for aerobic growth and CoQ9 biosynthesis. Deletion of ubiJPA, ubiBPA and ubiKPA led to reduced CoQ biosynthesis and an accumulation of the CoQ9 biosynthetic intermediate 3-nonaprenylphenol (NPP). Moreover, we also provide evidence that the truncated UbiJPA interacts with UbiBPA and UbiKPA to affect CoQ9 biosynthesis by forming a regulatory complex. The genetic diversity of coenzyme Q biosynthesis may provide targets for the future design of specific drugs to prevent P. aeruginosa-related infections.

Identification of a Combined RNA Prognostic Signature in Adenocarcinoma of the Lung

Background

Adenocarcinoma of the lung is a type of non-small cell lung cancer (NSCLC). Clinical outcome is associated with tumor grade, stage, and subtype. This study aimed to identify RNA expression profiles, including long noncoding RNA (lncRNA), microRNA (miRNA), and mRNA, associated with clinical outcome in adenocarcinoma of the lung using bioinformatics data.

Material/Methods

The miRNA and mRNA expression profiles were downloaded from The Cancer Genome Atlas (TCGA) database, and lncRNA expression profiles were downloaded from The Atlas of Noncoding RNAs in Cancer (TANRIC) database. The independent dataset, the Gene Expression Omnibus (GEO) accession dataset, GSE81089, was used. RNA expression profiles were used to identify comprehensive prognostic RNA signatures based on patient survival time.

Results

From 7,704 lncRNAs, 787 miRNAs, and 28,937 mRNAs of 449 patients, four joint RNA molecular signatures were identified, including RP11-909N17.2, RP11-14N7.2 (lncRNAs), MIR139 (miRNA), KLHDC8B (mRNA). The random forest (RF) classifier was used to test the prediction ability of patient survival risk and showed a good predictive accuracy of 71% and also showed a significant difference in overall survival (log-rank P=0.0002; HR, 3.54; 95% CI, 1.74–7.19). The combined RNA signature also showed good performance in the identification of patient survival in the validation and independent datasets.

Conclusions

This study identified four RNA sequences as a prognostic molecular signature in adenocarcinoma of the lung, which may also provide an increased understanding of the molecular mechanisms underlying the pathogenesis of this malignancy.

Comparative Genomic Analyses Reveal Core-Genome-Wide Genes Under Positive Selection and Major Regulatory Hubs in Outlier Strains of Pseudomonas aeruginosa

Genomic information for outlier strains of Pseudomonas aeruginosa is exiguous when compared with classical strains. We sequenced and constructed the complete genome of an environmental strain CR1 of P. aeruginosa and performed the comparative genomic analysis. It clustered with the outlier group, hence we scaled up the analyses to understand the differences in environmental and clinical outlier strains. We identified eight new regions of genomic plasticity and a plasmid pCR1 with a VirB/D4 complex followed by trimeric auto-transporter that can induce virulence phenotype in the genome of strain CR1. Virulence genotype analysis revealed that strain CR1 lacked hemolytic phospholipase C and D, three genes for LPS biosynthesis and had reduced antibiotic resistance genes when compared with clinical strains. Genes belonging to proteases, bacterial exporters and DNA stabilization were found to be under strong positive selection, thus facilitating pathogenicity and survival of the outliers. The outliers had the complete operon for the production of vibrioferrin, a siderophore present in plant growth promoting bacteria. The competence to acquire multidrug resistance and new virulence factors makes these strains a potential threat. However, we identified major regulatory hubs that can be used as drug targets against both the classical and outlier groups.

Employing metabolic engineered lipolytic microbial platform for 1-alkene one-step conversion

1-Alkenes are traditionally used as basic chemicals with great importance. Biosynthetic 1-alkenes also have the potential to serve as biofuels. In this study, we engineered a Pseudomonas lipolytic microbial platform for 1-alkene production using hydrophobic substrate as sole carbon source. Fatty acid decarboxylase UndA and UndB were cloned and expressed, which successfully produced 1-alkenes. Optimal culturing temperature and the interruption of competitive pathway were proven to be beneficial to 1-alkene synthesis. Chromosomal integration of UndB conferred 177.8 mg/L 1-alkenes (mainly 1-undecene) in lauric acid medium and 128.9 mg/L 1-alkenes (mainly 1-pentadecene) in palm oil medium. Thioesterase expression, adjustments of fatty acid degradation pathway and a second copy of UndB improved 1-alkene titer to 1102.6 mg/L using lauric acid and 778.4 mg/L using palm oil. All in all, this study offers the first demonstration of lipolytic microbial 1-alkene producing platform with highest reported 1-alkene product titer up to date.

Environmental reservoirs for exoS+ and exoU+ strains of Pseudomonas aeruginosa

Pseudomonas aeruginosa uses its type III secretion system to inject the effector proteins ExoS and ExoU into eukaryotic cells, which subverts these cells to the bacterium's advantage and contributes to severe infections. We studied the environmental reservoirs of exoS+ and exoU+ strains of P. aeruginosa by collecting water, soil, moist substrates and plant samples from environments in the Chicago region and neighbouring states. Whole-genome sequencing was used to determine the phylogeny and type III secretion system genotypes of 120 environmental isolates. No correlation existed between geographic separation of isolates and their genetic relatedness, which confirmed previous findings of both high genetic diversity within a single site and the widespread distribution of P. aeruginosa clonal complexes. After excluding clonal isolates cultured from the same samples, 74 exoS+ isolates and 16 exoU+ isolates remained. Of the exoS+ isolates, 41 (55%) were from natural environmental sites and 33 (45%) were from man-made sites. Of the exoU+ isolates, only 3 (19%) were from natural environmental sites and 13 (81%) were from man-made sites (p < 0.05). These findings suggest that man-made water systems may be a reservoir from which patients acquire exoU+ P. aeruginosa strains.

CrpP Is a Novel Ciprofloxacin-Modifying Enzyme Encoded by the Pseudomonas aeruginosa pUM505 Plasmid

The pUM505 plasmid, isolated from a clinical Pseudomonas aeruginosa isolate, confers resistance to ciprofloxacin (CIP) when transferred into the standard P. aeruginosa strain PAO1. CIP is an antibiotic of the quinolone family that is used to treat P. aeruginosa infections. In silico analysis, performed to identify CIP resistance genes, revealed that the 65-amino-acid product encoded by the orf131 gene in pUM505 displays 40% amino acid identity to the Mycobacterium smegmatis aminoglycoside phosphotransferase (an enzyme that phosphorylates and inactivates aminoglycoside antibiotics). We cloned orf131 (renamed crpP, for ciprofloxacin resistance protein, plasmid encoded) into the pUCP20 shuttle vector. The resulting recombinant plasmid, pUC-crpP, conferred resistance to CIP on Escherichia coli strain J53-3, suggesting that this gene encodes a protein involved in CIP resistance. Using coupled enzymatic analysis, we determined that the activity of CrpP on CIP is ATP dependent, while little activity against norfloxacin was detected, suggesting that CIP may undergo phosphorylation. Using a recombinant His-tagged CrpP protein and liquid chromatography-tandem mass spectrometry, we also showed that CIP was phosphorylated prior to its degradation. Thus, our findings demonstrate that CrpP, encoded on the pUM505 plasmid, represents a new mechanism of CIP resistance in P. aeruginosa, which involves phosphorylation of the antibiotic.

Indigenous Pseudomonas spp. Strains from the Olive (Olea europaea L.) Rhizosphere as Effective Biocontrol Agents against Verticillium dahliae: From the Host Roots to the Bacterial Genomes

The use of biological control agents (BCA), alone or in combination with other management measures, has gained attention over the past decades, driven by the need to seek for sustainable and eco-friendly alternatives to confront plant pathogens. The rhizosphere of olive (Olea europaea L.) plants is a source of bacteria with potential as biocontrol tools against Verticillium wilt of olive (VWO) caused by Verticillium dahliae Kleb. A collection of bacterial isolates from healthy nursery-produced olive (cultivar Picual, susceptible to VWO) plants was generated based on morphological, biochemical and metabolic characteristics, chemical sensitivities, and on their in vitro antagonistic activity against several olive pathogens. Three strains (PIC25, PIC105, and PICF141) showing high in vitro inhibition ability of pathogens' growth, particularly against V. dahliae, were eventually selected. Their effectiveness against VWO caused by the defoliating pathotype of V. dahliae was also demonstrated, strain PICF141 being the rhizobacteria showing the best performance as BCA. Genotypic and phenotypic traits traditionally associated with plant growth promotion and/or biocontrol abilities were evaluated as well (e.g., phytase, xylanase, catalase, cellulase, chitinase, glucanase activities, and siderophore and HCN production). Multi-locus sequence analyses of conserved genes enabled the identification of these strains as Pseudomonas spp. Strain PICF141 was affiliated to the “Pseudomonas mandelii subgroup,” within the “Pseudomonas fluorescens group,” Pseudomonas lini being the closest species. Strains PIC25 and PIC105 were affiliated to the “Pseudomonas aeruginosa group,” Pseudomonas indica being the closest relative. Moreover, we identified P. indica (PIC105) for the first time as a BCA. Genome sequencing and in silico analyses allowed the identification of traits commonly associated with plant-bacteria interactions. Finally, the root colonization ability of these olive rhizobacteria was assessed, providing valuable information for the future development of formulations based on these strains. A set of actions, from rhizosphere isolation to genome analysis, is proposed and discussed for selecting indigenous rhizobacteria as effective BCAs.

PhzA, the shunt switch of phenazine-1,6-dicarboxylic acid biosynthesis in Pseudomonas chlororaphis HT66

Natural phenazines are versatile secondary metabolites that are mainly produced by Pseudomonas and Streptomyces. All phenazine-type metabolites originate from two precursors: phenazine-1-carboxylic acid (PCA) in Pseudomonas or phenazine-1,6-dicarboxylic acid (PDC) in Streptomyces and other bacteria. Although the biosynthesis of PCA in Pseudomonas has been extensively studied, the origin of PDC still remains unclear. Comparing the phenazine biosynthesis operons of different species, we found that the phzA gene was restricted to Pseudomonas in which PCA is produced. By generating phzA-inactivated mutant, we found a new compound obviously accumulated; it was then isolated and identified as PDC. Protein sequence alignment showed that PhzA proteins from Pseudomonas form a separate group that is recognized by H73L and S77L mutations. Generating mutations of L⁷³ into H⁷³ and L⁷⁷ into S⁷⁷ resulted in a significant increase in PDC production. These findings suggest that phzA may act as a shunt switch of PDC biosynthesis in Pseudomonas and distinguish the pathway producing only PCA from the pathway forming PCA plus PDC. Using real-time PCR analysis, we suggested that the phzA, phzB, and phzG genes either directly or indirectly regulate the production of PDC, and phzA plays the most significant regulatory role. This is the first description of phzA in the biosynthesis of PDC, and the first-time substantial PDC was obtained in Pseudomonas. Therefore, this study not only provides valuable clues to better understand the biosynthesis of PCA and PDC in Pseudomonas but also introduces a method to produce PDC derivatives by genetically engineered strains.

Genomic analyses of multidrug resistant Pseudomonas aeruginosa PA1 resequenced by single-molecule real-time sequencing

As a third-generation sequencing (TGS) method, single-molecule real-time (SMRT) technology provides long read length, and it is well suited for resequencing projects and de novo assembly. In the present study, Pseudomonas aeruginosa PA1 was characterized and resequenced using SMRT technology. PA1 was also subjected to genomic, comparative and pan-genomic analyses. The multidrug resistant strain PA1 possesses a 6,498,072 bp genome and a sequence type of ST-782. The genome of PA1 was also visualized, and the results revealed the details of general genome annotations, virulence factors, regulatory proteins (RPs), secretion system proteins, type II toxin–antitoxin (T–A) pairs and genomic islands. Whole genome comparison analysis suggested that PA1 exhibits similarity to other P. aeruginosa strains but differs in terms of horizontal gene transfer (HGT) regions, such as prophages and genomic islands. Phylogenetic analyses based on 16S rRNA sequences demonstrated that PA1 is closely related to PAO1, and P. aeruginosa strains can be divided into two main groups. The pan-genome of P. aeruginosa consists of a core genome of approximately 4,000 genes and an accessory genome of at least 6,600 genes. The present study presented a detailed, visualized and comparative analysis of the PA1 genome, to enhance our understanding of this notorious pathogen.

iTRAQ-based quantitative proteomic analysis reveals potential factors associated with the enhancement of phenazine-1-carboxamide production in Pseudomonas chlororaphis P3

Phenazine-1-carboxamide (PCN), a phenazine derivative, is strongly antagonistic to fungal phytopathogens. Pseudomonas chlororaphis HT66 is a PCN-producing, non-pathogenic biocontrol strain, and we obtained the mutant P. chlororaphis P3, which produces 4.7 times more PCN than the wild-type HT66 strain. To reveal the cause of PCN production enhancement in P3 and find potential factors related to PCN biosynthesis, an iTRAQ-based quantitative proteomic analysis was used to study the expression changes between the two strains. Of the 452 differentially expressed proteins, most were functionally mapped into PCN biosynthesis pathway or other related metabolisms. The upregulation of proteins, including PhzA/B, PhzD, PhzF, PhzG, and PhzH, involved in PCN biosynthesis was in agreement with the efficient production of PCN in P3. A number of proteins that function primarily in energy production, amino acid metabolism, and secondary metabolism played important roles in PCN biosynthesis. Notably, proteins involved in the uptake and conversion of phosphate, inorganic nitrogen sources, and iron improved the PCN production. Furthermore, the type VI secretion system may participate in the secretion or/and indirect biosynthetic regulation of PCN in P. chlororaphis. This study provides valuable clues to better understand the biosynthesis, excretion and regulation of PCN in Pseudomonas and also provides potential gene targets for further engineering high-yield strains.

Genomic and Genetic Diversity within the Pseudomonas fluorescens Complex

The Pseudomonas fluorescens complex includes Pseudomonas strains that have been taxonomically assigned to more than fifty different species, many of which have been described as plant growth-promoting rhizobacteria (PGPR) with potential applications in biocontrol and biofertilization. So far the phylogeny of this complex has been analyzed according to phenotypic traits, 16S rDNA, MLSA and inferred by whole-genome analysis. However, since most of the type strains have not been fully sequenced and new species are frequently described, correlation between taxonomy and phylogenomic analysis is missing. In recent years, the genomes of a large number of strains have been sequenced, showing important genomic heterogeneity and providing information suitable for genomic studies that are important to understand the genomic and genetic diversity shown by strains of this complex. Based on MLSA and several whole-genome sequence-based analyses of 93 sequenced strains, we have divided the P. fluorescens complex into eight phylogenomic groups that agree with previous works based on type strains. Digital DDH (dDDH) identified 69 species and 75 subspecies within the 93 genomes. The eight groups corresponded to clustering with a threshold of 31.8% dDDH, in full agreement with our MLSA. The Average Nucleotide Identity (ANI) approach showed inconsistencies regarding the assignment to species and to the eight groups. The small core genome of 1,334 CDSs and the large pan-genome of 30,848 CDSs, show the large diversity and genetic heterogeneity of the P. fluorescens complex. However, a low number of strains were enough to explain most of the CDSs diversity at core and strain-specific genomic fractions. Finally, the identification and analysis of group-specific genome and the screening for distinctive characters revealed a phylogenomic distribution of traits among the groups that provided insights into biocontrol and bioremediation applications as well as their role as PGPR.

Comparative genomics and biological characterization of sequential Pseudomonas aeruginosa isolates from persistent airways infection

BACKGROUND

Pseudomonas aeruginosa establishes life-long chronic airway infections in cystic fibrosis (CF) patients. As the disease progresses, P. aeruginosa pathoadaptive variants are distinguished from the initially acquired strain. However, the genetic basis and the biology of host-bacteria interactions leading to a persistent lifestyle of P. aeruginosa are not understood. As a model system to study long term and persistent CF infections, the P. aeruginosa RP73, isolated 16.9 years after the onset of airways colonization from a CF patient, was investigated. Comparisons with strains RP1, isolated at the onset of the colonization, and clonal RP45, isolated 7 years before RP73 were carried out to better characterize genomic evolution of P. aeruginosa in the context of CF pathogenicity.

RESULTS

Virulence assessments in disease animal model, genome sequencing and comparative genomics analysis were performed for clinical RP73, RP45, RP1 and prototype strains. In murine model, RP73 showed lower lethality and a remarkable capability of long-term persistence in chronic airways infection when compared to other strains. Pathological analysis of murine lungs confirmed advanced chronic pulmonary disease, inflammation and mucus secretory cells hyperplasia. Genomic analysis predicted twelve genomic islands in the RP73 genome, some of which distinguished RP73 from other prototype strains and corresponded to regions of genome plasticity. Further, comparative genomic analyses with sequential RP isolates showed signatures of pathoadaptive mutations in virulence factors potentially linked to the development of chronic infections in CF.

CONCLUSIONS

The genome plasticity of P. aeruginosa particularly in the RP73 strain strongly indicated that these alterations may form the genetic basis defining host-bacteria interactions leading to a persistent lifestyle in human lungs.

Phylogenetic Distribution of CRISPR-Cas Systems in Antibiotic-Resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa is an antibiotic-refractory pathogen with a large genome and extensive genotypic diversity. Historically, P. aeruginosa has been a major model system for understanding the molecular mechanisms underlying type I clustered regularly interspaced short palindromic repeat (CRISPR) and CRISPR-associated protein (CRISPR-Cas)-based bacterial immune system function. However, little information on the phylogenetic distribution and potential role of these CRISPR-Cas systems in molding the P. aeruginosa accessory genome and antibiotic resistance elements is known. Computational approaches were used to identify and characterize CRISPR-Cas systems within 672 genomes, and in the process, we identified a previously unreported and putatively mobile type I-C P. aeruginosa CRISPR-Cas system. Furthermore, genomes harboring noninhibited type I-F and I-E CRISPR-Cas systems were on average ~300 kb smaller than those without a CRISPR-Cas system. In silico analysis demonstrated that the accessory genome (n = 22,036 genes) harbored the majority of identified CRISPR-Cas targets. We also assembled a global spacer library that aided the identification of difficult-to-characterize mobile genetic elements within next-generation sequencing (NGS) data and allowed CRISPR typing of a majority of P. aeruginosa strains. In summary, our analysis demonstrated that CRISPR-Cas systems play an important role in shaping the accessory genomes of globally distributed P. aeruginosa isolates.

IMPORTANCE

P. aeruginosa is both an antibiotic-refractory pathogen and an important model system for type I CRISPR-Cas bacterial immune systems. By combining the genome sequences of 672 newly and previously sequenced genomes, we were able to provide a global view of the phylogenetic distribution, conservation, and potential targets of these systems. This analysis identified a new and putatively mobile P. aeruginosa CRISPR-Cas subtype, characterized the diverse distribution of known CRISPR-inhibiting genes, and provided a potential new use for CRISPR spacer libraries in accessory genome analysis. Our data demonstrated the importance of CRISPR-Cas systems in modulating the accessory genomes of globally distributed strains while also providing substantial data for subsequent genomic and experimental studies in multiple fields. Understanding why certain genotypes of P. aeruginosa are clinically prevalent and adept at horizontally acquiring virulence and antibiotic resistance elements is of major clinical and economic importance.

Engineering the central biosynthetic and secondary metabolic pathways of Pseudomonas aeruginosa strain PA1201 to improve phenazine-1-carboxylic acid production

The secondary metabolite phenazine-1-carboxylic acid (PCA) is an important component of the newly registered biopesticide Shenqinmycin. We used a combined method involving gene, promoter, and protein engineering to modify the central biosynthetic and secondary metabolic pathways in the PCA-producing Pseudomonas aeruginosa strain PA1201. The PCA yield of the resulting strain PA-IV was increased 54.6-fold via the following strategies: (1) blocking PCA conversion and enhancing PCA efflux pumping; (2) increasing metabolic flux towards the PCA biosynthetic pathway through the over-production of two DAHP synthases and blocking the synthesis of 21 secondary metabolites; (3) increasing the PCA precursor supply through the engineering of five chorismate-utilizing enzymes; (4) engineering the promoters of two PCA biosynthetic gene clusters. Strain PA-IV produced 9882 mg/L PCA in fed-batch fermentation, which is twice as much as that produced by the current industrial strain. Strain PA-IV was also genetically stable and comparable to Escherichia coli in cytotoxicity.

Identification of the Lomofungin Biosynthesis Gene Cluster and Associated Flavin-Dependent Monooxygenase Gene in Streptomyces lomondensis S015

Streptomyces lomondensis S015 synthesizes the broad-spectrum phenazine antibiotic lomofungin. Whole genome sequencing of this strain revealed a genomic locus consisting of 23 open reading frames that includes the core phenazine biosynthesis gene cluster lphzGFEDCB. lomo10, encoding a putative flavin-dependent monooxygenase, was also identified in this locus. Inactivation of lomo10 by in-frame partial deletion resulted in the biosynthesis of a new phenazine metabolite, 1-carbomethoxy-6-formyl-4,9-dihydroxy-phenazine, along with the absence of lomofungin. This result suggests that lomo10 is responsible for the hydroxylation of lomofungin at its C-7 position. This is the first description of a phenazine hydroxylation gene in Streptomyces, and the results of this study lay the foundation for further investigation of phenazine metabolite biosynthesis in Streptomyces.

What It Takes to Be a Pseudomonas aeruginosa? The Core Genome of the Opportunistic Pathogen Updated

Pseudomonas aeruginosa is an opportunistic bacterial pathogen able to thrive in highly diverse ecological niches and to infect compromised patients. Its genome exhibits a mosaic structure composed of a core genome into which accessory genes are inserted en bloc at specific sites. The size and the content of the core genome are open for debate as their estimation depends on the set of genomes considered and the pipeline of gene detection and clustering. Here, we redefined the size and the content of the core genome of P. aeruginosa from fully re-analyzed genomes of 17 reference strains. After the optimization of gene detection and clustering parameters, the core genome was defined at 5,233 orthologs, which represented ~ 88% of the average genome. Extrapolation indicated that our panel was suitable to estimate the core genome that will remain constant even if new genomes are added. The core genome contained resistance determinants to the major antibiotic families as well as most metabolic, respiratory, and virulence genes. Although some virulence genes were accessory, they often related to conserved biological functions. Long-standing prophage elements were subjected to a genetic drift to eventually display a G+C content as higher as that of the core genome. This contrasts with the low G+C content of highly conserved ribosomal genes. The conservation of metabolic and respiratory genes could guarantee the ability of the species to thrive on a variety of carbon sources for energy in aerobiosis and anaerobiosis. Virtually all the strains, of environmental or clinical origin, have the complete toolkit to become resistant to the major antipseudomonal compounds and possess basic pathogenic mechanisms to infect humans. The knowledge of the genes shared by the majority of the P. aeruginosa isolates is a prerequisite for designing effective therapeutics to combat the wide variety of human infections.

Evolutionary insight from whole-genome sequencing of Pseudomonas aeruginosa from cystic fibrosis patients

ABSTRACT 

The opportunistic pathogen Pseudomonas aeruginosa causes chronic airway infections in patients with cystic fibrosis (CF), and it is directly associated with the morbidity and mortality connected with this disease. The ability of P. aeruginosa to establish chronic infections in CF patients is suggested to be due to the large genetic repertoire of P. aeruginosa and its ability to genetically adapt to the host environment. Here, we review the recent work that has applied whole-genome sequencing to understand P. aeruginosa population genomics, within-host microevolution and diversity, mutational mechanisms, genetic adaptation and transmission events. Finally, we summarize the advances in relation to medical applications and laboratory evolution experiments.

Regulation of gene expression in Pseudomonas aeruginosa M18 by phenazine-1-carboxylic acid

Phenazine-1-carboxylic acid (PCA), an environmentally compatible redox-active metabolite produced by Pseudomonas sp., has been found to effectively protect against various phytopathogens. The objective of this study was to discover whether PCA can also act as a signaling molecule that regulates gene expression in Pseudomonas aeruginosa M18. We constructed a series of PCA-producing mutant strains (high PCA, M18MSU1; low PCA, M18MS; and no PCA, M18MSP1P2) and analyzed their gene expression by using a custom microarray DNA chip. We found that the expression of PCA in both M18MSU1 and M18MS altered the expression of a total of 545 different genes; however, the higher level of PCA in M18MSU1 altered more genes (489) than did the lower level of PCA in M18MS (129). Of particular note, 73 of these genes were commonly regulated between the two mutants, indicating their importance in the downstream function of PCA. PCA molecules upregulated genes that function primarily in energy production, cell motility, secretion, and defense mechanisms and downregulated genes involved in transcription, translation, cell division, and gene expression in the prophage. We found that PCA worked to alter the expression of an efflux pump gene mexH through a SoxR-mediated mechanism; we further hypothesized that other pathways should also be affected by this interaction. Taken together, our results provide the first evidence of PCA-derived molecular responses at the transcriptional level. They also help to elucidate the future of genetically engineered P. aeruginosa strains for the production of PCA used in a number of applications.

Characterization of the core and accessory genomes of Pseudomonas aeruginosa using bioinformatic tools Spine and AGEnt

Background

Pseudomonas aeruginosa is an important opportunistic pathogen responsible for many infections in hospitalized and immunocompromised patients. Previous reports estimated that approximately 10% of its 6.6 Mbp genome varies from strain to strain and is therefore referred to as “accessory genome”. Elements within the accessory genome of P. aeruginosa have been associated with differences in virulence and antibiotic resistance. As whole genome sequencing of bacterial strains becomes more widespread and cost-effective, methods to quickly and reliably identify accessory genomic elements in newly sequenced P. aeruginosa genomes will be needed.

Results

We developed a bioinformatic method for identifying the accessory genome of P. aeruginosa. First, the core genome was determined based on sequence conserved among the completed genomes of twelve reference strains using Spine, a software program developed for this purpose. The core genome was 5.84 Mbp in size and contained 5,316 coding sequences. We then developed an in silico genome subtraction program named AGEnt to filter out core genomic sequences from P. aeruginosa whole genomes to identify accessory genomic sequences of these reference strains. This analysis determined that the accessory genome of P. aeruginosa ranged from 6.9-18.0% of the total genome, was enriched for genes associated with mobile elements, and was comprised of a majority of genes with unknown or unclear function. Using these genomes, we showed that AGEnt performed well compared to other publically available programs designed to detect accessory genomic elements. We then demonstrated the utility of the AGEnt program by applying it to the draft genomes of two previously unsequenced P. aeruginosa strains, PA99 and PA103.

Conclusions

The P. aeruginosa genome is rich in accessory genetic material. The AGEnt program accurately identified the accessory genomes of newly sequenced P. aeruginosa strains, even when draft genomes were used. As P. aeruginosa genomes become available at an increasingly rapid pace, this program will be useful in cataloging the expanding accessory genome of this bacterium and in discerning correlations between phenotype and accessory genome makeup. The combination of Spine and AGEnt should be useful in defining the accessory genomes of other bacterial species as well.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-737) contains supplementary material, which is available to authorized users.

Genome Sequencing of a Mung Bean Plant Growth Promoting Strain of P. aeruginosa with Biocontrol Ability

Pseudomonas aeruginosa PGPR2 is a mung bean rhizosphere strain that produces secondary metabolites and hydrolytic enzymes contributing to excellent antifungal activity against Macrophomina phaseolina, one of the prevalent fungal pathogens of mung bean. Genome sequencing was performed using the Ion Torrent Personal Genome Machine generating 1,354,732 reads (6,772,433 sequenced bases) achieving ~25-fold coverage of the genome. Reference genome assembly using MIRA 3.4.0 yielded 198 contigs. The draft genome of PGPR2 encoded 6803 open reading frames, of which 5314 were genes with predicted functions, 1489 were genes of known functions, and 80 were RNA-coding genes. Strain specific and core genes of P. aeruginosa PGPR2 that are relevant to rhizospheric habitat were identified by pangenome analysis. Genes involved in plant growth promoting function such as synthesis of ACC deaminase, indole-3-acetic acid, trehalose, mineral scavenging siderophores, hydrogen cyanide, chitinases, acyl homoserine lactones, acetoin, 2,3-butanediol, and phytases were identified. In addition, niche-specific genes such as phosphate solubilising 3-phytase, adhesins, pathway-specific transcriptional regulators, a diguanylate cyclase involved in cellulose synthesis, a receptor for ferrienterochelin, a DEAD/DEAH-box helicase involved in stress tolerance, chemotaxis/motility determinants, an HtpX protease, and enzymes involved in the production of a chromanone derivative with potent antifungal activity were identified.

Ribosomally encoded antibacterial proteins and peptides from Pseudomonas

Members of the Pseudomonas genus produce diverse secondary metabolites affecting other bacteria, fungi or predating nematodes and protozoa but are also equipped with the capacity to secrete different types of ribosomally encoded toxic peptides and proteins, ranging from small microcins to large tailocins. Studies with the human pathogen Pseudomonas aeruginosa have revealed that effector proteins of type VI secretion systems are part of the antibacterial armamentarium deployed by pseudomonads. A novel class of antibacterial proteins with structural similarity to plant lectins was discovered by studying antagonism among plant-associated Pseudomonas strains. A genomic perspective on pseudomonad bacteriocinogeny shows that the modular architecture of S pyocins of P. aeruginosa is retained in a large diversified group of bacteriocins, most of which target DNA or RNA. Similar modularity is present in as yet poorly characterized Rhs (recombination hot spot) proteins and CDI (contact-dependent inhibition) proteins. Well-delimited domains for receptor recognition or cytotoxicity enable the design of chimeric toxins with novel functionalities, which has been applied successfully for S and R pyocins. Little is known regarding how these antibacterials are released and ultimately reach their targets. Other remaining issues concern the identification of environmental triggers activating these systems and assessment of their ecological impact in niches populated by pseudomonads.

Pseudomonas aeruginosa clinical and environmental isolates constitute a single population with high phenotypic diversity

Background

Pseudomonas aeruginosa is an opportunistic pathogen with a high incidence of hospital infections that represents a threat to immune compromised patients. Genomic studies have shown that, in contrast to other pathogenic bacteria, clinical and environmental isolates do not show particular genomic differences. In addition, genetic variability of all the P. aeruginosa strains whose genomes have been sequenced is extremely low. This low genomic variability might be explained if clinical strains constitute a subpopulation of this bacterial species present in environments that are close to human populations, which preferentially produce virulence associated traits.

Results

In this work, we sequenced the genomes and performed phenotypic descriptions for four non-human P. aeruginosa isolates collected from a plant, the ocean, a water-spring, and from dolphin stomach. We show that the four strains are phenotypically diverse and that this is not reflected in genomic variability, since their genomes are almost identical. Furthermore, we performed a detailed comparative genomic analysis of the four strains studied in this work with the thirteen previously reported P. aeruginosa genomes by means of describing their core and pan-genomes.

Conclusions

Contrary to what has been described for other bacteria we have found that the P. aeruginosa core genome is constituted by a high proportion of genes and that its pan-genome is thus relatively small. Considering the high degree of genomic conservation between isolates of P. aeruginosa from diverse environments, including human tissues, some implications for the treatment of infections are discussed. This work also represents a methodological contribution for the genomic study of P. aeruginosa, since we provide a database of the comparison of all the proteins encoded by the seventeen strains analyzed.

The interaction pattern between a homology model of 40S ribosomal S9 protein of Rhizoctonia solani and 1-hydroxyphenaize by docking study

1-Hydroxyphenazine (1-OH-PHZ), a natural product from Pseudomonas aeruginosa strain SD12, was earlier reported to have potent antifungal activity against Rhizoctonia solani. In the present work, the antifungal activity of 1-OH-PHZ on 40S ribosomal S9 protein was validated by molecular docking approach. 1-OH-PHZ showed interaction with two polar contacts with residues, Arg69 and Phe19, which inhibits the synthesis of fungal protein. Our study reveals that 1-OH-PHZ can be a potent inhibitor of 40S ribosomal S9 protein of R. solani that may be a promising approach for the management of fungal diseases.

Genomic analysis of Pseudomonas aeruginosa PA96, the host of carbapenem resistance plasmid pOZ176

Pseudomonas aeruginosa PA96 is a clinical isolate from Guangzhou, China, that is multiresistant to antibiotics. We previously described the 500-kb IncP-2 plasmid, pOZ176 that encodes many resistance genes including the IMP-9 carbapenemase. Whole-genome sequencing of PA96 enabled characterization of its genomic islands, virulence factors, and chromosomal resistance genes. We filled gaps using PCR and used optical mapping to confirm the correct contig order. We automatically annotated the core genome and manually annotated the genomic islands. The genome is 6 444 091 bp and encodes 5853 ORFs. From the whole-genome sequence, we constructed a physical map and constructed a phylogenetic tree for comparison with sequenced P. aeruginosa strains. Analysis of known core genome virulence factors and resistance genes revealed few differences with other strains, but the major virulence island is closer to that of DK2 than to PA14. PA96 most closely resembles the environmental strain M18, and notably shares a common serotype, pyoverdin type, flagellar operon, type IV pilin, and several genomic islands with M18.

Bacterial genome instability

Bacterial genomes are remarkably stable from one generation to the next but are plastic on an evolutionary time scale, substantially shaped by horizontal gene transfer, genome rearrangement, and the activities of mobile DNA elements. This implies the existence of a delicate balance between the maintenance of genome stability and the tolerance of genome instability. In this review, we describe the specialized genetic elements and the endogenous processes that contribute to genome instability. We then discuss the consequences of genome instability at the physiological level, where cells have harnessed instability to mediate phase and antigenic variation, and at the evolutionary level, where horizontal gene transfer has played an important role. Indeed, this ability to share DNA sequences has played a major part in the evolution of life on Earth. The evolutionary plasticity of bacterial genomes, coupled with the vast numbers of bacteria on the planet, substantially limits our ability to control disease.

From the environment to the host: re-wiring of the transcriptome of Pseudomonas aeruginosa from 22°C to 37°C

Pseudomonas aeruginosa is a highly versatile opportunistic pathogen capable of colonizing multiple ecological niches. This bacterium is responsible for a wide range of both acute and chronic infections in a variety of hosts. The success of this microorganism relies on its ability to adapt to environmental changes and re-program its regulatory and metabolic networks. The study of P. aeruginosa adaptation to temperature is crucial to understanding the pathogenesis upon infection of its mammalian host. We examined the effects of growth temperature on the transcriptome of the P. aeruginosa PAO1. Microarray analysis of PAO1 grown in Lysogeny broth at mid-exponential phase at 22°C and 37°C revealed that temperature changes are responsible for the differential transcriptional regulation of 6.4% of the genome. Major alterations were observed in bacterial metabolism, replication, and nutrient acquisition. Quorum-sensing and exoproteins secreted by type I, II, and III secretion systems, involved in the adaptation of P. aeruginosa to the mammalian host during infection, were up-regulated at 37°C compared to 22°C. Genes encoding arginine degradation enzymes were highly up-regulated at 22°C, together with the genes involved in the synthesis of pyoverdine. However, genes involved in pyochelin biosynthesis were up-regulated at 37°C. We observed that the changes in expression of P. aeruginosa siderophores correlated to an overall increase in Fe²⁺ extracellular concentration at 37°C and a peak in Fe³⁺ extracellular concentration at 22°C. This suggests a distinct change in iron acquisition strategies when the bacterium switches from the external environment to the host. Our work identifies global changes in bacterial metabolism and nutrient acquisition induced by growth at different temperatures. Overall, this study identifies factors that are regulated in genome-wide adaptation processes and discusses how this life-threatening pathogen responds to temperature.

Advances in understanding Pseudomonas

Pseudomonas aeruginosa, the type species of pseudomonads, is an opportunistic pathogen that colonizes a wide range of niches. Current genome sequencing projects are producing previously inconceivable detail about the population biology and evolution of P. aeruginosa. Its pan-genome has a larger genetic repertoire than the human genome, which explains the broad metabolic capabilities of P. aeruginosa and its ubiquitous distribution in aquatic habitats. P. aeruginosa may persist in the airways of individuals with cystic fibrosis for decades. The ongoing whole-genome analyses of serial isolates from cystic fibrosis patients provide the so far singular opportunity to monitor the microevolution of a bacterial pathogen during chronic infection over thousands of generations. Although the evolution in cystic fibrosis lungs is neutral overall, some pathoadaptive mutations are selected during the within-host evolutionary process. Even a single mutation may be sufficient to generate novel complex traits provided that predisposing mutational events have previously occurred in the clonal lineage.

Draft genomes of 12 host-adapted and environmental isolates of Pseudomonas aeruginosa and their positions in the core genome phylogeny

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen particularly associated with the inherited disease cystic fibrosis (CF). Pseudomonas aeruginosa is well known to have a large and adaptable genome that enables it to colonise a wide range of ecological niches. Here, we have used a comparative genomics approach to identify changes that occur during infection of the CF lung. We used the mucoid phenotype as an obvious marker of host adaptation and compared these genomes to analyse SNPs, indels and islands within near-isogenic pairs. To commence the correction of the natural bias towards clinical isolates in genomics studies and to widen our understanding of the genomic diversity of P. aeruginosa, we included four environmental isolates in our analysis. Our data suggest that genome plasticity plays an important role in chronic infection and that the strains sequenced in this study are representative of the two major phylogenetic groups as determined by core genome SNP analysis.

Global transcriptome analysis of Lactococcus garvieae strains in response to temperature

Lactococcus garvieae is an important fish and an opportunistic human pathogen. The genomic sequences of several L. garvieae strains have been recently published, opening the possibility of global studies on the biology of this pathogen. In this study, a whole genome DNA microarray of two strains of L. garvieae was designed and validated. This DNA microarray was used to investigate the effects of growth temperature (18°C and 37°C) on the transcriptome of two clinical strains of L. garvieae that were isolated from fish (Lg8831) and from a human case of septicemia (Lg21881). The transcriptome profiles evidenced a strain-specific response to temperature, which was more evident at 18°C. Among the most significant findings, Lg8831 was found to up-regulate at 18°C several genes encoding different cold-shock and cold-induced proteins involved in an efficient adaptive response of this strain to low-temperature conditions. Another relevant result was the description, for the first time, of respiratory metabolism in L. garvieae, whose gene expression regulation was temperature-dependent in Lg21881. This study provides new insights about how environmental factors such as temperature can affect L. garvieae gene expression. These data could improve our understanding of the regulatory networks and adaptive biology of this important pathogen.

Identification and structure elucidation of a novel antifungal compound produced by Pseudomonas aeruginosa PGPR2 against Macrophomina phaseolina

Pseudomonas aeruginosa PGPR2 was found to protect mungbean plants from charcoal rot disease caused by Macrophomina phaseolina. Secondary metabolites from the culture supernatant of P. aeruginosa PGPR2 were extracted with ethyl acetate and the antifungal compound was purified by preparative HPLC using reverse phase chromatography. The purified compound showed antifungal activity against M. phaseolina and other phytopathogenic fungi (Fusarium sp., Rhizoctonia sp. Alternaria sp., and Aspergillus sp.). The structure of the purified compound was determined using (1)H, (13)C, 2D NMR spectra and liquid chromatography-mass spectrometry (LC-MS). Spectral data suggest that the antifungal compound is 3,4-dihydroxy-N-methyl-4-(4-oxochroman-2-yl)butanamide, with the chemical formula C14H17NO5 and a molecular mass of 279. Though chemically synthesized chromanone derivatives have been shown to have antifungal activity, we report for the first time, the microbial production of a chromanone derivative with antifungal activity. This ability of P. aeruginosa PGPR2 makes it a suitable strain for biocontrol.

Global control of GacA in secondary metabolism, primary metabolism, secretion systems, and motility in the rhizobacterium Pseudomonas aeruginosa M18

The rhizobacterium Pseudomonas aeruginosa M18 can produce a broad spectrum of secondary metabolites, including the antibiotics pyoluteorin (Plt) and phenazine-1-carboxylic acid (PCA), hydrogen cyanide, and the siderophores pyoverdine and pyochelin. The antibiotic biosynthesis of M18 is coordinately controlled by multiple distinct regulatory pathways, of which the GacS/GacA system activates Plt biosynthesis but strongly downregulates PCA biosynthesis. Here, we investigated the global influence of a gacA mutation on the M18 transcriptome and related metabolic and physiological processes. Transcriptome profiling revealed that the transcript levels of 839 genes, which account for approximately 15% of the annotated genes in the M18 genome, were significantly influenced by the gacA mutation during the early stationary growth phase of M18. Most secondary metabolic gene clusters, such as pvd, pch, plt, amb, and hcn, were activated by GacA. The GacA regulon also included genes encoding extracellular enzymes and cytochrome oxidases. Interestingly, the primary metabolism involved in the assimilation and metabolism of phosphorus, sulfur, and nitrogen sources was also notably regulated by GacA. Another important category of the GacA regulon was secretion systems, including H1, H2, and H3 (type VI secretion systems [T6SSs]), Hxc (T2SS), and Has and Apr (T1SSs), and CupE and Tad pili. More remarkably, GacA inhibited swimming, swarming, and twitching motilities. Taken together, the Gac-initiated global regulation, which was mostly mediated through multiple regulatory systems or factors, was mainly involved in secondary and primary metabolism, secretion systems, motility, etc., contributing to ecological or nutritional competence, ion homeostasis, and biocontrol in M18.

Comparative genomic analysis of four representative plant growth-promoting rhizobacteria in Pseudomonas

Background

Some Pseudomonas strains function as predominant plant growth-promoting rhizobacteria (PGPR). Within this group, Pseudomonas chlororaphis and Pseudomonas fluorescens are non-pathogenic biocontrol agents, and some Pseudomonas aeruginosa and Pseudomonas stutzeri strains are PGPR. P. chlororaphis GP72 is a plant growth-promoting rhizobacterium with a fully sequenced genome. We conducted a genomic analysis comparing GP72 with three other pseudomonad PGPR: P. fluorescens Pf-5, P. aeruginosa M18, and the nitrogen-fixing strain P. stutzeri A1501. Our aim was to identify the similarities and differences among these strains using a comparative genomic approach to clarify the mechanisms of plant growth-promoting activity.

Results

The genome sizes of GP72, Pf-5, M18, and A1501 ranged from 4.6 to 7.1 M, and the number of protein-coding genes varied among the four species. Clusters of Orthologous Groups (COGs) analysis assigned functions to predicted proteins. The COGs distributions were similar among the four species. However, the percentage of genes encoding transposases and their inactivated derivatives (COG L) was 1.33% of the total genes with COGs classifications in A1501, 0.21% in GP72, 0.02% in Pf-5, and 0.11% in M18. A phylogenetic analysis indicated that GP72 and Pf-5 were the most closely related strains, consistent with the genome alignment results. Comparisons of predicted coding sequences (CDSs) between GP72 and Pf-5 revealed 3544 conserved genes. There were fewer conserved genes when GP72 CDSs were compared with those of A1501 and M18. Comparisons among the four Pseudomonas species revealed 603 conserved genes in GP72, illustrating common plant growth-promoting traits shared among these PGPR. Conserved genes were related to catabolism, transport of plant-derived compounds, stress resistance, and rhizosphere colonization. Some strain-specific CDSs were related to different kinds of biocontrol activities or plant growth promotion. The GP72 genome contained the cus operon (related to heavy metal resistance) and a gene cluster involved in type IV pilus biosynthesis, which confers adhesion ability.

Conclusions

Comparative genomic analysis of four representative PGPR revealed some conserved regions, indicating common characteristics (metabolism of plant-derived compounds, heavy metal resistance, and rhizosphere colonization) among these pseudomonad PGPR. Genomic regions specific to each strain provide clues to its lifestyle, ecological adaptation, and physiological role in the rhizosphere.

Friend or foe: genetic and functional characterization of plant endophytic Pseudomonas aeruginosa

Endophytic Pseudomonas aeruginosa strain BP35 was originally isolated from black pepper grown in the rain forest in Kerala, India. Strain PaBP35 was shown to provide significant protection to black pepper against infections by Phytophthora capsici and Radopholus similis. For registration and implementation in disease management programmes, several traits of PaBP35 were investigated including its endophytic behaviour, biocontrol activity, phylogeny and toxicity to mammals. The results showed that PaBP35 efficiently colonized black pepper shoots and displayed a typical spatiotemporal pattern in its endophytic movement with concomitant suppression of Phytophthora rot. Confocal laser scanning microscopy revealed high populations of PaBP35::gfp2 inside tomato plantlets, supporting its endophytic behaviour in other plant species. Polyphasic approaches to genotype PaBP35, including BOX-PCR, recN sequence analysis, multilocus sequence typing and comparative genome hybridization analysis, revealed its uniqueness among P. aeruginosa strains representing clinical habitats. However, like other P. aeruginosa strains, PaBP35 exhibited resistance to antibiotics, grew at 25-41°C and produced rhamnolipids and phenazines. PaBP35 displayed strong type II secretion effectors-mediated cytotoxicity on mammalian A549 cells. Coupled with pathogenicity in a murine airway infection model, we conclude that this plant endophytic strain is as virulent as clinical P. aeruginosa strains. Safety issues related to the selection of plant endophytic bacteria for crop protection are discussed.