Bile salt tolerance enhancement and survival mechanism in Limosilactobacillus fermentum M2 mediated by Kluyveromyces marxianus Y4.

Enhancing the survival capacity of probiotic strains under bile salt (BS) stress via probiotic interactions constitutes a highly prospective novel strategy within the domain of probiotic applications. In this study, based on probiotic characterization of two probiotic strains, designated Limosilactobacillus fermentum M2 and Kluyveromyces marxianus Y4, the viable counts of L. fermentum M2 under BS stress reached from 9.1 to 7.34 log CFU/mL, while co-culture with K. marxianus Y4 significantly increased the survival of L.fermentum M2 by 76.4% compared with monoculture (p < 0.05). In contrast, no significant difference was observed under non - BS stress conditions. Meanwhile metabolites of BS treatment K. marxianus Y4 (BSTKM) enhanced the survival ability of L.fermentum M2 exposed to BS. The observations of the microbial microstructure confirm that BSTKM exerts a protective effect by preserving the structural integrity of L.fermentum M2. Subsequently, metabolomic analysis was performed to identify differential metabolites between BSTKM and BS, while proteomic profiling was used to investigate the differential protein expression in L.fermentum M2 under BSTKM and BS stress. Integrated multi - omics analysis suggested that differential metabolites such as biotin, amino acids, and purines may be associated with DNA repair processes, thereby enhancing the survival ability of L.fermentum M2 under BS stress. This study provides a theoretical foundation for improving the survivability of lactic acid bacteria (LAB) under BS conditions and proposes new perspectives on LAB - yeast symbiotic interactions.