Species- and salt-dependent Mg2+ handling during fermentation - Comparative responses of Saccharomyces boulardii and Lactobacilli.

Magnesium is an essential cofactor in microbial metabolism, and its availability during fermentation can substantially influence probiotic growth, metabolic activity, and intracellular mineral handling. This study aimed to evaluate the influence of four magnesium salts, bisglycinate, malate, citrate, and taurate, on fermentation performance, metabolism, and cell-associated magnesium accumulation in three microorganisms: Saccharomyces boulardii MYA-796, Lacticaseibacillus rhamnosus ATCC 53103, and Limosilactobacillus fermentum LC-40. Fermentation assays revealed pronounced strain- and salt-dependent responses. S. boulardii exhibited enhanced viability in the presence of Mg-mal and a marked shift in fermentation metabolism, characterized by a ∼50% reduction in ethanol production and distinct changes in extracellular malic and citric acid levels between T0 and T24. L. rhamnosus benefited primarily from Mg-cit and Mg-mal, maintaining higher cell counts and improved pH stability, whereas L. fermentum sustained robust growth across all treatments with mainly quantitative changes in organic acid profiles. Analysis of cell-associated magnesium accumulation identified S. boulardii as the strain exhibiting the highest magnesium accumulation capacity, reaching nearly 700 μg/g DW with Mg-tau, compared to less than 270 μg/g DW in lactic acid bacteria (LAB). Docking simulations supported these findings, identifying yeast ALR1 as having the highest binding potential score (∼4.9), whereas LAB MgtE showed only moderate binding potential. These results indicate that S. boulardii accumulates magnesium levels up to 4-fold higher than those of the LAB strains tested, highlighting its suitability as a model system for studying mineral accumulation and metabolic adaptation under magnesium-enriched fermentation conditions.