Mechanistic insights into strain-specific lactiplantibacillus-yeast interactions in a wheat-based system:...

Lactic acid bacteria (LAB) and yeasts interactions in sourdough fermentation directly influence product consistency and flavor. In this study, we investigated interaction mechanisms between Lactiplantibacillus plantarum Lp100 and two pHylogenetically distinct yeasts, Maudiozyma humilis Mh2 and Saccharomyces cerevisiae Sc4 in a liquid wheat-based medium (CBFM) by characterizing population dynamics, cell morphology, and metabolic interplay. Lp100 rapidly acidified coculture environment, resulting in pH-mediated inhibition of both yeasts, with Mh2 showing greater acid tolerance than Sc4. Growth assays using Lp100-derived cell-free supernatants (with and without pH adjustment) showed that both acidification and additional metabolites jointly shape microbial competitiveness. Whereas yeast supernatants were compatible with Lp100 growth. Moreover, Transwell experiments further revealed spatial heterogeneity in metabolite diffusion, with yeast growth significantly higher in inserts than in wells, thereby indicating that acidification together with other diffusible metabolites contributed to the observed inhibitory effects. Time-resolved metabolomics uncovered strain-specific responses to coculture-induced environmental and metabolic challenges. In Lp100 + Mh2 cocultures, carbon metabolism was rerouted toward fermentation pathways and glutathione precursors (e.g. γ-glutamylcysteine) with concurrent accumulation of reduced riboflavin. These changes point to adjustments in redox-related metabolism of Mh2 under coculture conditions. Conversely, Lp100 + Sc4 cocultures displayed signs of oxidative stress, including elevated levels of amino sugar and tryptophan catabolites, and suppressed nucleotide metabolism, indicating distinct metabolite-driven stress responses in Sc4. Together, these findings reveal mechanisms insight into LAB-yeast coculture dynamics and highlight the importance of strain compatibility. Such insights support rational design of sourdough starter cultures and improve stability and quality of cereal fermentations through targeted management of acid and redox conditions.