In situ activity of a bacteriocin-producing Lactococcus lactis strain. Influence on the interactions between lactic acid bacteria during sourdough fermentation.

Aims: To biochemically characterize the bacteriocin produced by Lactococcus lactis ssp. lactis M30 and demonstrate its effect on lactic acid bacteria (LAB) during sourdough propagation.

Methods And Results: A two-peptide bacteriocin produced by L. lactis ssp. lactis M30 was purified by ion exchange, hydrophobic interaction and reversed phase chromatography. Mass spectrometry of the two peptides and sequence analysis of the ltnA2 gene showed that the bacteriocin was almost identical to lacticin 3147. During a 20-day period of sourdough propagation the stability of L. lactis M30 was demonstrated, with concomitant inhibition of the indicator strain Lactobacillus plantarum 20, as well as the non-interference with the growth of the starter strain Lact. sanfranciscensis CB1.

Conclusions: In situ active bacteriocins influence the microbial consortium of sourdough LAB and can "support" the dominance of insensitive strains during sourdough fermentation.

Significance And Impact Of The Study: The in situ bacteriocinogenic activity of selected lactococci enables the persistence of insensitive Lact. sanfranciscensis strains, useful to confer good characteristics to the dough, at a higher cell concentration with respect to other LAB of the same ecosystem.