Abstract
Proteinases and bacteriocins are of great importance to the dairy industry, but their interactions have not been studied so far. Lactococcus lactis subsp. lactis BGMN1-5 is a natural isolate from homemade semi-hard cheese which produces two bacteriocins (Lactococcin B and LsbB), as well as proteinase PrtP. A medium-dependent increase in the bacteriocin LcnB activity of L. lactis BGMN1-501, a derivate of L. lactis subsp. lactis BGMN1-5, was shown to be accompanied by a decrease in its promoter activity. A similar effect of media components on gene expression was reported for proteinase PrtP, whose gene is co-localized on the same plasmid as the lcnB gene. Thus, the PrtP-LcnB interplay was investigated. Single gene knockout mutants were constructed with disrupted prtP or lcnB genes. PrtP- mutants showed higher bacteriocin activity that had lost its growth medium dependence, which was in contrast to the original strain. When LcnB from this mutant was combined with proteinase from the LcnB- mutant in vitro, its activity was rendered to the original level, suggesting that proteinase reduces bacteriocin activity. We propose a new model of medium dependent expression of these genes with regard to the effects of their interaction in vivo.
Highlights
Lactococcus lactis is the best characterized species of lactic acid bacteria (LAB) and one of the most studied and utilized Grampositive bacteria
Pulsed-field gel electrophoresis (PFGE) (SmaI macrorestriction) analysis of BGMN1-501, transformants with free constructs and mutants confirmed the integration of constructs into plasmid pMN80 at different positions
BACTERIOCIN ACTIVITY IS MEDIUM DEPENDENT IN BGMN1-501, BUT NOT IN BGMN1-501/pG+HOST9prtP (ITS PrtP− MUTANT) The bacteriocin activity of BGMN1-501 and its PrtP− mutant was analyzed after 16 h of growth in GM17 with different concentrations of casitone (0% w/v, 0.5% w/v, 1% w/v, 2% w/v, 4% w/v, 6% w/v, and 8% w/v), assayed by the agar well diffusion test on indicator strain BGMN1-596
Summary
Lactococcus lactis is the best characterized species of lactic acid bacteria (LAB) and one of the most studied and utilized Grampositive bacteria. It is used as a starter culture for manufacturing a wide variety of fermented milk products, either as a single culture or in a mixture with other LAB. It’s most important trait is the production of lactic acid and the acidification of milk, which is used in numerous ways in the production of fermented milk products. It leads to curdling of milk and at the same time prevents the growth of undesirable bacteria. The occurrence and composition of bioactive peptides depend mainly on the substrate specificity of proteinases applied in food processing
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