Cloning and sequencing of sakP encoding sakacin P, the bacteriocin produced by Lactobacillus sake LTH 673

Sakacin P is a heat-stable, unmodified peptide bacteriocin produced by Lactobacillus sake LTH 673. The strain was isolated from fermented dry sausages and is well adapted to this habitat. The bacteriocin inhibits the growth of the opportunistic food pathogens Enterococcus faecalis and Listeria monocytogenes and therefore, it may improve the hygienic status of fermented food, i.e. meat products. Oligonucleotide probes were designed from the N-terminal amino acid sequence of sakacin P and used to identify sakP, the structural gene of sakacin P, on the chromosome of L. sake LTH 673. SakP was cloned into Escherichia coli NM554 and the nucleotide sequence of the gene and its adjacent regions were determined. Sakacin P appears to be synthesized as a prepeptide of 61 amino acids which is proteolytically processed to the mature bacteriocin consisting of 43 amino acids. Sequencing of the cloned fragment also revealed the presence of two other open reading frames orfX and orfY, which are located upstream and downstream of sakP, respectively, putatively encoding proteins of 52 and 98 amino acids, respectively. The functions of both ORFs remain unknown. Primer extension analysis revealed a promoter upstream of sakP. Two transcripts of approximately 0.35 and 1.0 kb were detected by Northern hybridization encoding either only sakP, or both sakP and orfY, respectively.