Multilocus sequence typing of Propionibacterium freudenreichii

Area of Science:

• Microbiology
• Food Science
• Genomics

Background:

• Propionibacterium freudenreichii is crucial for Swiss cheese ripening.
• Understanding its genetic diversity is key to optimizing cheese production.

Purpose of the Study:

• To investigate the molecular diversity and population structure of P. freudenreichii using multilocus sequence typing (MLST).
• To assess the relationship between genotype, phenotype, and ecological niche.

Main Methods:

• Sequencing of internal fragments from seven genes across 113 P. freudenreichii strains.
• Multilocus sequence typing (MLST) to define sequence types (STs).
• Phenotypic characterization focusing on lactose and nitrate utilization.

Main Results:

• 46 distinct sequence types (STs) were identified among the 113 strains.
• The core genome exhibits low nucleotide polymorphism (0.46% average pairwise).
• Recombination and mutation contribute comparably to genetic variation.
• No significant dairy biotope specialization was observed among STs.
• Phenotypic heterogeneity, including lactose and nitrate use, was high even within STs.
• Existing subspecies classifications do not align with ancestral relationships.

Conclusions:

• P. freudenreichii populations possess low overall genetic diversity but high phenotypic heterogeneity.
• The data suggests a history of recurrent phenotypic switching rather than stable biotype specialization.
• Current subspecies do not accurately represent the evolutionary history of P. freudenreichii.