Cloning, sequencing and expression in Escherichia coli of lcnB, a third bacteriocin determinant from the lactococcal bacteriocin plasmid p9B4-6

Article Abstract:

Two bacteriocin determinants of Lactoccocus lactis subspecie cremoris plasmid p9B4-6 was previously characterized in recent studies. A third one was identified in this study. Subjection to an in vitro deletion and mutagenesis of the lactococcus plasmid fragment showed that it contained two genes for bacteriocin production and immunity. These two genes were transcribed as an operon and were found to contain similar nucleotide sequence similar to the previously characterized bacteriocins. Its specificity to lactococcin B as shown from results of cloning procedure was different from that of the other two bacteriocins. Antimicrobial activity was detected during transcription of the operon using Escherichia coli as its expression system. The identification of this new genetic determinant of lactococcin B provides the lactococcus strain with an advantage over other bacteriocin-producing lactoccci.

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Cloning, expression, and chromosomal stabilization of the Propionibacterium shermanii proline iminopeptidase gene (pip) for food-grade application in Lactococcus lactis

Article Abstract:

A study was conducted to characterize the proline iminopeptidase of Propionibacterium shermanii ATCC 9617 and the nucleotide sequence of the pip gene. Escherichia coli and L. lactis were altered by electrotransformation while a culture of P. shermanii was determined at the late logarithmic phase. The Pierce bicinchoninic protein assay reagent was utilized to determine protein concentrations. Results indicated that the pip gene was inhibited during the presence of another proline iminopeptidase activity.

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The mode of replication is a major factor in segregational plasmid instability in Lactococcus lactis

Article Abstract:

The effects of DNA insert size on the modes of replication for the maintenance of recombinant plasmids in Lactococcus lactis are discussed. Plasmid fragments of the rolling-circle (RCR) and theta types were subjected to molecular cloning, gel electrophoresis, Southern hybridizations and segregational stability assays. The superiority of theta-type plasmids over RCR-types for cloning L. lactis was demonstrated.

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