Integrated Growth Physiology and Transcriptome Profiling Uncover Probiotic Adaptability of Limosilactobacillus fermentum KUB-D18

Limosilactobacillus fermentum KUB-D18 is a probiotic strain with significant potential in food fermentation and health promotion, yet the systems-level mechanisms underlying its physiological robustness remain elusive. To elucidate the metabolic remodeling strategies operating across growth phases, we developed an integrated framework combining genome-scale metabolic modeling (GSMM) with transcriptomics. A high-quality metabolic model for L. fermentum KUB-D18, designated iYH640 and comprising 640 genes, 1530 metabolites, and 1922 reactions, was constructed and validated against experimental growth data. Specifically, in vitro assays measuring biomass and glucose concentrations showed a maximum specific growth rate of 0.2696 h−1 and a glucose uptake rate of 11.75 mmol gDCW−1 h−1, providing physiological constraints for the model. Using transcriptome-regulated flux balance analysis (TR-FBA), gene expression profiles from the logarithmic phase (L-phase) and stationary phase (S-phase) were integrated to quantify growth phase-specific metabolic flux distributions. These simulations revealed a distinct transcription-driven metabolic shift, in which the organism moves from a proliferation-oriented metabolic state with active central carbon metabolism and macromolecule synthesis to a maintenance-oriented state. This S-phase is characterized by reduced flux through anabolic pathways together with the selective preservation of redox balance and nucleotide homeostasis. Collectively, these results provide a quantitative explanation of how L. fermentum KUB-D18 balances growth and maintenance, offering a mechanistic basis for improving its stability and functional performance in industrial probiotic applications.