Application of culture and molecular methods to study the microbial dynamics underlying the production of a naturally fermented milk

Abstract

The aim of this research was to study the succession of the three components of a microbial consortium driving milk fermentation in an artisanal naturally-fermented milk (NFM); i.e., Lactococcus lactis LA1, Lactococcus cremoris LA10, and Lactiplantibacillus plantarum LA30. In order to obtain a realistic snapshot of the microbial dynamics of the NFM, the growth of the three strains in milk was evaluated individually and in all possible mixes by combining culture-based and qPCR (specific target-gene of strain) methodologies. When cultured alone, L. cremoris LA10 reached maximum cell numbers of 6x108 cfu/ml, while L. Lactis LA1 and L. plantarum LA30 reached, respectively, a cell density of 0.5 and 1.5 log units lower. The counts of L. lactis LA1 in milk were only increased in co-culture with L. cremoris LA10, whereas counts of the L. cremoris strain remained unchanged from those obtained alone. By the cultured-based approach, partial inhibition of L. plantarum LA30 by the two lactococci was observed at the beginning of the fermentation; however, this effect was not clearly detected by qPCR. Except for this result, culture and qPCR counts along fermentation agree well. During storage of the NFM at 4 ºC, L. plantarum LA30 counts remained stable for up to 25 days. In contrast, the viability of the two lactococci strains dropped drastically during storage, except in the co-cultures with L. plantarum. The knowledge acquired will help shed light on the complex relationships of the three strains in the consortium.