Insecticidal features displayed by the beneficial rhizobacterium Pseudomonas chlororaphis PCL1606

The biocontrol rhizobacterium Pseudomonas chlororaphis is one of the bacterial species of the P. fuorescens group where insecticide ft genes have been found. Fit toxin, supported with other antimicrobial compounds, gives the bacterial the ability to repel and to fght against eukaryotic organisms, such as nematodes and insect larvae, thus protecting the plant host and itself. Pseudomonas chlororaphis PCL1606 is an antagonistic rhizobacterium isolated from avocado roots and show efcient biocontrol against fungal soil-borne disease. The main antimicrobial compound produced by P. chlororaphis PCL606 is 2-hexyl-5-propyl resorcinol (HPR), which plays a crucial role in efective biocontrol against fungal pathogens. Further analysis of the P. chlororaphis PCL1606 genome showed the presence of hydrogen cyanide (HCN), pyrrolnitrin (PRN), and homologous ft genes. To test the insecticidal activity and to determine the bases for such activity, single and double mutants on the biosynthetic genes of these four compounds were tested in a Galleria mellonella larval model using inoculation by injection. The results revealed that Fit toxin and HPR in combination are involved in the insecticide phenotype of P. chlororaphis PCL1606, and additional compounds such as HCN and PRN could be considered supporting compoundsOpen Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Funding for open access charge: Universidad de Málaga / CBUA. This work was supported by the research project AGL2017-83368-CO2-1-R of Ministerio de Ciencias y Tecnología, and the project UMA-FEDERJA-046 of Junta de Andalucía

The Iturin and Fengycin Families of Lipopeptides Are Key Factors in Antagonism of Bacillus subtilis Toward Podosphaera fusca

Podosphaera fusca is the main causal agent of cucurbit powdery mildew in Spain. Four Bacillus subtilis strains, UMAF6614, UMAF6619, UMAF6639, and UMAF8561, with proven ability to suppress the disease on melon in detached leaf and seedling assays, were subjected to further analyses to elucidate the mode of action involved in their biocontrol performance. Cell-free supernatants showed antifungal activities very close to those previously reported for vegetative cells. Identification of three lipopeptide antibiotics, surfactin, fengycin, and iturin A or bacillomycin, in butanolic extracts from cell-free culture filtrates of these B. subtilis strains pointed out that antibiosis could be a major factor involved in their biocontrol ability. The strong inhibitory effect of purified lipopeptide fractions corresponding to bacillomycin, fengycin, and iturin A on P. fusca conidia germination, as well as the in situ detection of these lipopeptides in bacterial-treated melon leaves, provided interesting evidence of their putative involvement in the antagonistic activity. Those results were definitively supported by site-directed mutagenesis analysis, targeted to suppress the biosynthesis of the different lipopeptides. Taken together, our data have allowed us to conclude that the iturin and fengycin families of lipopeptides have a major role in the antagonism of B. subtilis toward P. fusca.

The Iturin and Fengycin Families of Lipopeptides Are Key Factors in Antagonism of Bacillus subtilis Toward Podosphaera fusca

Podosphaera fusca is the main causal agent of cucurbit powdery mildew in Spain. Four Bacillus subtilis strains, UMAF6614, UMAF6619, UMAF6639, and UMAF8561, with proven ability to suppress the disease on melon in detached leaf and seedling assays, were subjected to further analyses to elucidate the mode of action involved in their biocontrol performance. Cell-free supernatants showed antifungal activities very close to those previously reported for vegetative cells. Identification of three lipopeptide antibiotics, surfactin, fengycin, and iturin A or bacillomycin, in butanolic extracts from cell-free culture filtrates of these B. subtilis strains pointed out that antibiosis could be a major factor involved in their biocontrol ability. The strong inhibitory effect of purified lipopeptide fractions corresponding to bacillomycin, fengycin, and iturin A on P. fusca conidia germination, as well as the in situ detection of these lipopeptides in bacterial-treated melon leaves, provided interesting evidence of their putative involvement in the antagonistic activity. Those results were definitively supported by site-directed mutagenesis analysis, targeted to suppress the biosynthesis of the different lipopeptides. Taken together, our data have allowed us to conclude that the iturin and fengycin families of lipopeptides have a major role in the antagonism of B. subtilis toward P. fusca.

Aislamiento de cepas de Pseudomonas syringae pv. syringae asociadas a mango para su uso en análisis evolutivos y epidemiológicos

Comunicación oralLa necrosis apical del mango (NAM) es una enfermedad que se ha observado en el litoral andaluz desde la implantación de este cultivo, y cuyo agente causal es la bacteria Pseudomonas syringae pv. syringae (Pss). Esta enfermedad aparece principalmente asociada a climas con inviernos frescos y húmedos, tal y como ocurre en la cuenca mediterránea, donde, además de en España, se ha descrito en otros países (Israel, Portugal, Italia, Egipto), así como en otras áreas de cultivo con clima similar, como el Noroeste de Australia. Las cepas de Pss aisladas de mango muestran características importantes para su biología, tanto a nivel de virulencia como de fitness epifítico. En trabajos previos se han descrito diferentes genes implicados en el desarrollo de los síntomas de la enfermedad, así como en aumentar la capacidad de la bacteria de sobrevivir y persistir sobre el tejido vegetal; el operón mbo implicado en la producción de mangotoxina, los genes copABCD o cusCBA, implicados en la capacidad de resistencia al cobre, o el operón wss, responsable de la producción de celulosa. Por otro lado, gracias a análisis filogenéticos, se ha podido agrupar a todas las cepas de Pss aisladas de mango y productoras de mangotoxinas en el filotipo I. El objetivo de este trabajo es el análisis fenético comparado de cepas de Pss aisladas de mango de las diferentes zonas de estudio (España, Portugal, Italia, Australia), antes del año 2000 (colección I) y disponibles en nuestro laboratorio, con aislamientos actuales (2016-2018, Colección II). Este estudio se ha iniciado con la caracterización y selección previa de cepas representativas de cada una de las colecciones, para iniciar un abordaje en detalle y comparación de los diferentes atributos.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Nephroprotective Effect of the Virgin Olive Oil Polyphenol Hydroxytyrosol in Type 1-like Experimental Diabetes Mellitus: Relationships with Its Antioxidant Effect

The aim of this study was to determine whether hydroxytyrosol administration prevented kidney damage in an experimental model of type 1 diabetes mellitus in rats. Hydroxytyrosol was administered to streptozotocin-diabetic rats: 1 and 5 mg/kg/day p.o. for two months. After hydroxytyrosol administration, proteinuria was significantly reduced (67–73%), calculated creatinine clearance was significantly increased (26–38%), and the glomerular volume and glomerulosclerosis index were decreased (20–30%). Hydroxytyrosol reduced oxidative and nitrosative stress variables and thromboxane metabolite production. Statistical correlations were found between biochemical and kidney function variables. Oral administration of 1 and 5 mg/kg/day of hydroxytyrosol produced an antioxidant and nephroprotective effect in an experimental model of type 1-like diabetes mellitus. The nephroprotective effect was significantly associated with the systemic and renal antioxidant action of hydroxytyrosol, which also influenced eicosanoid production

The Compound 2-Hexyl, 5-Propyl Resorcinol Has a Key Role in Biofilm Formation by the Biocontrol Rhizobacterium Pseudomonas chlororaphis PCL1606

The production of the compound 2-hexyl-5-propyl resorcinol (HPR) by the biocontrol rhizobacterium Pseudomonas chlororaphis PCL1606 (PcPCL1606) is crucial for fungal antagonism and biocontrol activity that protects plants against the phytopathogenic fungus Rosellinia necatrix. The production of HPR is also involved in avocado root colonization during the biocontrol process. This pleiotrophic response prompted us to study the potential role of HPR production in biofilm formation. The swimming motility of PcPLL1606 is enhanced by the disruption of HPR production. Mutants impaired in HPR production, revealed that adhesion, colony morphology, and typical air–liquid interphase pellicles were all dependent on HPR production. The role of HPR production in biofilm architecture was also analyzed in flow chamber experiments. These experiments revealed that the HPR mutant cells had less tight unions than those producing HPR, suggesting an involvement of HPR in the production of the biofilm matrix

The mbo Operon Is Specific and Essential for Biosynthesis of Mangotoxin in Pseudomonas syringae

Mangotoxin is an antimetabolite toxin produced by certain Pseudomonas syringae pv. syringae strains. This toxin is an oligopeptide that inhibits ornithine N-acetyl transferase, a key enzyme in the biosynthesis of ornithine and arginine. Previous studies have reported the involvement of the putative nonribosomal peptide synthetase MgoA in virulence and mangotoxin production. In this study, we analyse a new chromosomal region of P. syringae pv. syringae UMAF0158, which contains six coding sequences arranged as an operon (mbo operon). The mbo operon was detected in only mangotoxin-producing strains, and it was shown to be essential for the biosynthesis of this toxin. Mutants in each of the six ORFs of the mbo operon were partially or completely impaired in the production of the toxin. In addition, Pseudomonas spp. mangotoxin non-producer strains transformed with the mbo operon gained the ability to produce mangotoxin, indicating that this operon contains all the genetic information necessary for mangotoxin biosynthesis. The generation of a single transcript for the mbo operon was confirmed and supported by the allocation of a unique promoter and Rho-independent terminator. The phylogenetic analysis of the P. syringae strains harbouring the mbo operon revealed that these strains clustered together

Bestatin is a non-competitive inhibitor of porcine M1 family glutamyl aminopeptidase: Insights for selective inhibitor design

Glutamyl aminopeptidase (APA) is an M1 family membrane-bound ectoenzyme that is a target for the development of antihypertensive and anticancer agents. Bestatin is a natural product described as a classical inhibitor of metallo-aminopeptidases. Although the IC50 value of bestatin vs human APA has been reported, the mechanism of inhibition is unknown. In the present contribution, we demonstrated that bestatin is a non-competitive (α>1) inhibitor of porcine APA (pAPA), with a Ki value of 31.59 µM (α=3.7). A model of the bestatin-pAPA complex predicted that bestatin binds to pAPA similarly to porcine aminopeptidase N (pAPN). The interaction involved catalytic and chelating residues conserved in the M1 family. Additionally, a salt bridge with R877 and a hydrogen bond interaction with T346, both key residues for APA specificity for N-terminal acidic residues were identified. These residues and E213, which forms a hydrogen bond interaction with bestatin, are not conserved in human and porcine APN. The extension of the in silico analysis to amastatin and bestatin analogs probestin, and phebestin, which are APA inhibitors, indicated that they may interact with the same residues. The results indicate that bestatin analogues currently reported to inhibit APN are dual inhibitors of APA and APN and that some APA residues could be targeted to improve inhibitor selectivity

Bestatin is a non-competitive inhibitor of porcine M1 family glutamyl aminopeptidase: Insights for selective inhibitor design

173-180Glutamyl aminopeptidase (APA) is an M1 family membrane-bound ectoenzyme that is a target for the development of antihypertensive and anticancer agents. Bestatin is a natural product described as a classical inhibitor of metallo-aminopeptidases. Although the IC50 value of bestatin vs human APA has been reported, the mechanism of inhibition is unknown. In the present contribution, we demonstrated that bestatin is a non-competitive (α>1) inhibitor of porcine APA (pAPA), with a Ki value of 31.59 μM (α=3.7). A model of the bestatin-pAPA complex predicted that bestatin binds to pAPA similarly to porcine aminopeptidase N (pAPN). The interaction involved catalytic and chelating residues conserved in the M1 family. Additionally, a salt bridge with R877 and a hydrogen bond interaction with T346, both key residues for APA specificity for N-terminal acidic residues were identified. These residues and E213, which forms a hydrogen bond interaction with bestatin, are not conserved in human and porcine APN. The extension of the in silico analysis to amastatin and bestatin analogs probestin, and phebestin, which are APA inhibitors, indicated that they may interact with the same residues. The results indicate that bestatin analogues currently reported to inhibit APN are dual inhibitors of APA and APN and that some APA residues could be targeted to improve inhibitor selectivity

RNA-seq Analysis Reveals That an ECF σ Factor, AcsS, Regulates Achromobactin Biosynthesis in Pseudomonas syringae pv. syringae B728a

Iron is an essential micronutrient for Pseudomonas syringae pv. syringae strain B728a and many other microorganisms; therefore, B728a has evolved methods of iron acquirement including the use of iron-chelating siderophores. In this study an extracytoplasmic function (ECF) sigma factor, AcsS, encoded within the achromobactin gene cluster is shown to be a major regulator of genes involved in the biosynthesis and secretion of this siderophore. However, production of achromobactin was not completely abrogated in the deletion mutant, implying that other regulators may be involved such as PvdS, the sigma factor that regulates pyoverdine biosynthesis. RNA-seq analysis identified 287 genes that are differentially expressed between the AcsS deletion mutant and the wild type strain. These genes are involved in iron response, secretion, extracellular polysaccharide production, and cell motility. Thus, the transcriptome analysis supports a role for AcsS in the regulation of achromobactin production and the potential activity of both AcsS and achromobactin in the plant-associated lifestyle of strain B728a