Propionicin SM1, a bacteriocin from Propionibacterium jensenii DF1: Isolation and characterization of the protein and its gene

We purified a bacteriocin from the cell-free supernatant of Propionibacteri um jensenii DF1 isolated from Swiss raw milk, and named it propionicin SM1. The heat-stable protein was strongly bactericidal against P. jensenii DSM2 0274. On the basis of the N-terminal amino acid sequence of the purified pr otein, a degenerate oligonucleotide probe was designed to locate and clone the corresponding gene of P. jensenii DF1. It hybridized exclusively with t he DF1-resident plasmid pI.ME106, but not with chromosomal DNA. Sequencing of the 6.9-kb plasmid revealed the targeted amino acid sequence within an o pen reading frame (ORF4) of 207 amino acids (molecular mass, 22'865 Da). Th e corresponding gene was named ppnA. It encodes the prepeptide PpnA that is processed to the mature protein (19'942 Da) propionicin SM1. No sequence h omology is detectable with known proteins. However, the proposed leader pep tide sequence containing 27 amino acids has typical signal peptide features and shows good homology to the leader peptide of Usp45, a protein excreted from Lactococcus lactis (VAN ASSELDONK et al., 1993). Plasmid pLME106 cont ains at least 9 ORFs, some exhibiting significant homologies to plasmid-enc oded functions from other bacteria. The highest identity values were found for ORF1 with the theta replicase (acc. no. U39878) of Brevibacterium linen s (58.8%) and ORF6 with the recombinase/invertase (acc. no. AF060871) found in Rhodococcus rhodochrous (46.4%).