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.