<jats:title>ABSTRACT</jats:title> <jats:p> A collection of propionibacteria was screened for bacteriocin production. A new bacteriocin named propionicin T1 was isolated from two strains of <jats:italic>Propionibacterium thoenii</jats:italic> . This bacteriocin shows no sequence similarity to other bacteriocins. Propionicin T1 was active against all strains of <jats:italic>Propionibacterium acidipropionici</jats:italic> , <jats:italic>Propionibacterium thoenii</jats:italic> , and <jats:italic>Propionibacterium jensenii</jats:italic> tested and also against <jats:italic>Lactobacillus sake</jats:italic> NCDO 2714 but showed no activity against <jats:italic>Propionibacterium freudenreichii</jats:italic> . The bacteriocin was purified, and the N-terminal part of the peptide was determined with amino acid sequencing. The corresponding gene <jats:italic>pctA</jats:italic> was sequenced, and this revealed that propionicin T1 is produced as a prebacteriocin of 96 amino acids with a typical <jats:italic>sec</jats:italic> leader, which is processed to give a mature bacteriocin of 65 amino acids. An open reading frame encoding a protein of 424 amino acids was found 68 nucleotides downstream the stop codon of <jats:italic>pctA</jats:italic> . The N-terminal part of this putative protein shows strong similarity with the ATP-binding cassette of prokaryotic and eukaryotic ABC transporters, and this protein may be involved in self-protection against propionicin T1. Propionicin T1 is the first bacteriocin from propionibacteria that has been isolated and further characterized at the molecular level.