Pantocin A and pantocin B are low-molecular weight, peptide-based antibiotics that are produced in minimal media by the biocontrol agent Pantoea agglomerans, which are inhibitory to the fire blight pathogen, Erwinia amylovora. Pantocin A and pantocin B are members of a family of antibiotics whose toxicity is inhibited by certain amino acids. They inhibit enzymes in pathways for histidine and arginine biosynthesis, respectively. The biosynthetic gene cluster for pantocin A was sequenced, and it is 2.84 kb in size. It contains a small gene (paaP) that encodes a thirty-amino acid precursor peptide and three genes, paaA, paaB and paaC that encode the enzymes necessary to process the precursor into pantocin A. PaaC is proposed to be responsible for resistance to pantocin A. The determinants for pantocin B biosynthesis are encoded in a cluster of 13 open reading frames (PabA through pabM within a 17.5 kb region. Functions are proposed for the individual gene products, based on DNA sequence homology and on the chemical structure of pantocin B. PabA is similar to multidrug resistance proteins (like YqjV of Bacmus subtilis) and is likely responsible for pantocin B resistance. However, pabB, pabC and pabD may also encode resistance determinants. The products of the pabJKLM operon are believed to be involved in the addition of the methyl sulfonyl moiety of pantocin B. Cryptic transposase genes are found within and outside of the biosynthetic region, and the G+C ratio is lower inside than outside of the cluster. Thus, the pantocin B biosynthetic region may be a genomic island whose DNA originated from other organisms and was generated through two separate transposition events.