The genetic drift in Lacticaseibacillus paracasei DG over ten years of industrial production

The commercialization of a probiotic strain assumes that all production lots are equivalent. However, the microbial biomasses of a probiotic are produced industrially in large quantities, repeatedly and continuously for years, and could be therefore potentially subject to genetic drift, which may affect its ability to confer health benefits to the host. In this study, we assessed the stability of Lacticaseibacillus paracasei DG (DSM 34154), a well-characterized commercial probiotic strain, by analyzing 8 isolates from different production lots over the past 10 years, an isolate from 8 years of subculturing in the lab, and the DG strain deposited in the DSMZ culture collection. We found that the genome organization of the L. paracasei DG strain remained largely unchanged, with all 10 isolates harboring the two plasmids present in the original strain and only a few point mutations compared to the reference genome of the DSMZ collection, none of which affected putative coding sequences. Moreover, phenotypic analyses of the 10 isolates, including resistance to simulated gastrointestinal transit, immunomodulatory capacity, adhesion to Caco-2 cell layer, fermentation profile, antibiotic resistance, and modulation of transepithelial electric resistance, revealed no significant differences. Overall, our study demonstrates that the isolates of the L. paracasei DG strain derived from industrial productions over the past 10 years are substantially equivalent in terms of genotype and phenotype. Similar quality control measures should be periodically conducted to ensure that probiotic properties and intended health benefits are preserved.