Lactococcus kimchii extends lifespan and alleviates motility decline in Caenorhabditis elegans through ins-20, an insulin-like peptide gene

Lactococcus kimchii is isolated from commercial kimchi, which is a traditional Korean fermented food. This study was conducted to evaluate the probiotic effects of L. kimchii. Caenorhabditis elegans was fed L. kimchii, and its longevity, motility, and gene expression were examined. When fed a 1:1 mixture of Escherichia coli OP50 and L. kimchii (OP+LK), C. elegans had a significantly longer lifespan and increased locomotion than when it was fed OP alone. There was no significant difference in brood size between the OP+LK and OP groups, suggesting that these effects occurred in a dietary restriction-independent manner. RNA sequencing and Gene Ontology analysis showed that the expression of ins-20, an insulin-like peptide and agonist of the insulin receptor, was significantly upregulated in the OP+LK group. The ins-20 mutation annulled the effects of OP+LK on lifespan extension and motility. In addition, OP+LK failed to extend the lifespan of C. elegans deficient in daf-2, a receptor for the insulin-like signaling pathway. These results suggest that L. kimchii extends the lifespan and alleviates motility decline in C. elegans through the insulin signaling pathway, highlighting the potential of using L. kimchii as a beneficial bacterium for probiotics and postbiotics.