Intracellular and Extracellular Metabolic Response of the Lactic Acid Bacterium Under Salt Stress.

Background: is a member of the lactic acid bacterium group commonly found in many salt-fermented foods. Strains of isolated from high-salinity environments have been shown to tolerate salt stress to some extent. However, the specific responses and mechanisms of under salt stress are not fully understood.

Methods: To study the effect of NaCl stress on , growth performance and metabolite profiles of the strains were compared between a NaCl-free group and a 35% NaCl-treated group. Growth performance was assessed by measuring viable cell counts and examining the cells using scanning electron microscopy (SEM). Intracellular and extracellular metabolites were analyzed by non-targeted metabolomics based on liquid chromatography-mass spectrometry (LC-MS).

Results: It was found that the viable cell count of decreased with increasing salinity, and cells could survive even in saturated saline (35%) medium for 24 h. When exposed to 35% NaCl, cells exhibited surface pores and protein leakage. Based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, 42 different metabolites were identified in the cells and 18 different metabolites in the culture medium. These different metabolites were mainly involved in amino acid metabolism, carbohydrate metabolism, and nucleotide metabolism. In addition, salt-exposed cells exhibited higher levels of intracellular ectoine and lactose, whose precursors, such as aspartate, L-2,4-diaminobutanoate, and galactinol, were reduced in the culture medium.

Conclusions: This study provides insight into the metabolic responses of under salt stress, revealing its ability to maintain viability and alter metabolism in response to high NaCl concentrations. Key metabolites such as ectoine and lactose, as well as changes in amino acid and nucleotide metabolism, may contribute to its tolerance to salt. These findings may improve our understanding of the bacterium's survival mechanisms and have potential applications in food fermentation and biotechnology.