The histidine-reversible antibiotic herbicolin O produced by Pantoea vagans C9-1 is pantocin A

Pantoea vagans C9-1 is one of the most effective and reliable biocontrol agents against fire blight, and has been commercialized as Blight Ban C9-1. Production of multiple antibiotics contributes to its antagonism of Erwinia amylovora. Here we describe the genetics, chemical isolation and structure of herbicolin O, the histidine-reversible antibiotic produced by P. vagans C9-1. Mutational analyses indicated that biosynthesis of herbicolin O depends on paaAB and a sequence encoding the peptide precursor of pantocin A. The paaABC gene cluster encoding biosynthesis and autoresistance was located within a 28-kb chromosomal genomic island of the complete genome sequence of P. vagans C9-1. The cluster was cloned and expressed in E. coli and purified antibiotic was isolated using improved methods for small peptides. The¹H NMR spectra of the C9-1 antibiotic closely resembled those of pantocin A produced by P. agglomerans Eh318. Detailed analysis of the proton spin systems showed that the chemical shift values and coupling constants of the protons in C9-1 herbicolin O correspond exactly to those of pantocin A. Based on these genetic and chemical analyses, herbicolin O and pantocin A are confirmed to be the same antibiotic.