Lactococcus lactis subsp. lactis boosts stress resistance and host defense mechanisms in Caenorhabditis elegans

To investigate the effects of Lactococcus lactis subsp. lactis strains LL100933 and LL12007 on the host defense mechanisms of Caenorhabditis elegans against pathogenic infections and stressors. Caenorhabditis elegans fed a 1:1 mixture of Escherichia coli OP50 and LL100933 (OP50 + LL100933) or E. coli OP50 and LL12007 (OP50 + LL12007) had significantly higher survivability than the control diet (OP50). Moreover, when OP50 + LL100933 and OP50 + LL12007 were fed to C. elegans deficient in daf-16 and pmk-1, survival did not exceed that of control-fed worms under Salmonella infection. Therefore, these strains may enhance the survivability of C. elegans through the p38 MAPK and DAF-16-related pathways. Gene expressions responsible for these enhanced defense responses were estimated using RNA sequencing and gene ontology analysis. The test groups showed significant upregulation of glutathione S-transferase (gsto-1, gst-5, and gst-17), UDP-glucuronyl transferase (ugt-13, ugt-16, and ugt-21), heme-responsive (hrg-4), invertebrate-type lysozyme (ilys-2), and C-type lectin (clec-52) genes compared to those in the control group. Lactococcus lactis subsp. lactis LL100933 and LL12007 strains demonstrated promising benefits as probiotics for enhancing host defense mechanisms in C. elegans.