# Genetic Characterisation of Closely Related Lactococcus lactis Strains Used in Dairy Starter Cultures

## TL;DR

This study explores the genetic makeup of Lactococcus lactis strains in a Russian artisanal cheese starter, revealing three distinct strains and their lack of typical aroma compound production.

## Contribution

The study provides a detailed genetic and functional characterization of closely related Lactococcus lactis strains in a specific cheese starter.

## Key findings

- Metagenomic analysis identified three Lactococcus lactis genomes in the cheese starter.
- Isolates were grouped into three distinct strains based on rpoB gene analysis.
- None of the strains produced diacetyl or CO2, characteristic of L. l. subsp. diacetilactis.

## Abstract

The complex microbiota of cheese starters plays a key role in determining the structure and flavour of the final product, primarily through their acid-forming capacity, protease activity, and exopolysaccharide synthesis. However, the specific microbial communities underlying the unique qualities of artisanal cheeses remain poorly understood. This study presents the microbiological and molecular genetic characterisation of the microbiome isolated from an artisanal cheese starter in Kosh-Agach, Altai, Russia. Metagenomic analysis of this starter revealed the presence of three bacterial genomes corresponding to those of Lactococcus lactis. Pure cultures from this starter were obtained by sequential subculture, and seventeen colonies displaying distinct characteristics on differential media were selected. Genome sequencing was performed for each colony. Bioinformatic analysis based on the rpoB gene grouped the isolates into three clusters, each corresponding to a distinct strain of Lactococcus lactis subsp. diacetilactis. This classification was further confirmed by microbiological and microscopic analyses. A notable finding was that none of the strains produced the characteristic aroma compounds of L. l. subsp. diacetilactis, namely, diacetyl and CO2. The functional properties and metabolic characteristics of this starter consortium are discussed.