Detección e identificación molecular de Pantoea vagans en flores de Dahlia sp.

Las Dalias (Dahlia spp.) son flores nativas de Mesoamérica y endémicas de México. Su consumo como alimento es una práctica antigua, en la actualidad es escasa la información y reglamentación sanitaria para su comercialización y consumo. Al respecto, el objetivo del presente estudio fue identificar morfológica, bioquímica y molecularmente, bacterias de origen entérico asociadas con flores de Dalia. Los resultados de la caracterización morfológica revelaron la predominancia de bacilos cortos Gram negativos. A partir de la observación de la morfología colonial en medios de cultivo selectivos y diferenciales se identificaron como Escherichia coli y Salmonella spp. Sin embargo, el uso de un método comercial automatizado los clasifica como Enterobacter cancerogenus. Debido a que ambas pruebas arrojaron resultados distintos en cuanto a la identidad del microorganismo aislado, no fueron concluyentes. Por lo tanto, se recurrió a la caracterización molecular para la identificación del aislado bacteriano. La bacteria predominante en flores de Dalia, correspondió a Pantoea vagans (Número de acceso CP002206). Éste es el primer reporte de Pantoea vagans aislada de flores de Dalia.

Comparative Genomics Analysis of Plasmid pPV989-94 from a Clinical Isolate ofPantoea vagansPV989

Pantoea vagans, a gram-negative bacterium from the genusPantoeaand familyEnterobacteriaceae, is present in various natural environments and considered to be plant endophytes. We isolated thePantoea vagansPV989 strain from the clinic and sequenced its whole genome. Besides a chromosome DNA molecule, it also harboured three large plasmids. A comparative genomics analysis was performed for the smallest plasmid, pPV989-94. It can be divided into four regions, including three conservative regions related to replication (R1), transfer conjugation (R2), and transfer leading (R3), and one variable region (R4). Further analysis showed that pPV989-94 is most similar to plasmids LA637P2 and pEA68 ofErwinia amylovorastrains isolated from fruit trees. These three plasmids share three conservative regions (R1, R2, and R3). Interestingly, a fragment (R4′) in R4, mediated by phage integrase and phage integrase family site-specific recombinase and encoding 9 genes related to glycometabolism, resistance, and DNA repair, was unique in pPV989-94. Homologues of R4′were found in other plasmids or chromosomes, suggesting that horizontal gene transfer (HGT) occurred among different bacteria of various species or genera. The acquired functional genes may play important roles in the adaptation of bacteria to different hosts or environmental conditions.

Characterization of the Biosynthetic Operon for the Antibacterial Peptide Herbicolin in Pantoea vagans Biocontrol Strain C9-1 and Incidence in Pantoea Species

ABSTRACTPantoea vagansC9-1 is a biocontrol strain that produces at least two antibiotics inhibiting the growth ofErwinia amylovora, the causal agent of fire blight disease of pear and apple. One antibiotic, herbicolin I, was purified from culture filtrates ofP. vagansC9-1 and determined to be 2-amino-3-(oxirane-2,3-dicarboxamido)-propanoyl-valine, also known asNß-epoxysuccinamoyl-DAP-valine. A plasposon library was screened for mutants that had lost the ability to produce herbicolin I. It was shown that mutants had reduced biocontrol efficacy in immature pear assays. The biosynthetic gene cluster inP. vagansC9-1 was identified by sequencing the flanking regions of the plasposon insertion sites. The herbicolin I biosynthetic gene cluster consists of 10 coding sequences (CDS) and is located on the 166-kb plasmid pPag2. Sequence comparisons identified orthologous gene clusters inPantoea agglomeransCU0119 andSerratia proteamaculans568. A low incidence of detection of the biosynthetic cluster in a collection of 45Pantoeaspp. from biocontrol, environmental, and clinical origins showed that this is a rare trait among the tested strains.

Control of Fire Blight by Pseudomonas fluorescens A506 and Pantoea vagans C9-1 Applied as Single Strains and Mixed Inocula

The biological control agents Pseudomonas fluorescens A506 and Pantoea vagans C9-1 were evaluated individually and in combination for the suppression of fire blight of pear or apple in 10 field trials inoculated with the pathogen Erwinia amylovora. The formulation of pathogen inoculum applied to blossoms influenced establishment of the pathogen and the efficacy of biological control. Pantoea vagans C9-1 suppressed fire blight in all five trials in which the pathogen was applied as lyophilized cells but in none of the trials in which the pathogen was applied as freshly harvested cells. In contrast, Pseudomonas fluorescens A506 reduced disease significantly in only one trial. A mixture of the two strains also suppressed fire blight, but the magnitude of disease suppression over all field trials (averaging 32%) was less than that attained by C9-1 alone (42%). The two biological control agents did not antagonize one another on blossom surfaces, and application of the mixture of A506 and C9-1 to blossoms resulted in a greater proportion of flowers having detectable populations of at least one bacterial antagonist than the application of individual strains. Therefore, the mixture of A506 and C9-1 provided less disease control than expected based upon the epiphytic population sizes of the antagonists on blossom surfaces. We speculate that the biocontrol mixture was less effective than anticipated due to incompatibility between the mechanisms by which A506 and C9-1 suppress disease.