Euglena gracilis-derived β-1,3-glucan as a growth substrate for Lactococcus lactis-a snapshot of accompanying changes in transcriptomic and metabolomic profiles.

β-1,3-glucan from Euglena gracilis is an emerging microalgal prebiotic. However, its potential to reprogram the metabolic profile of lactic acid bacteria has not been reported previously. In the present study, the effects of insoluble β-1,3-glucan on growth dynamics, gene expression, and the extracellular metabolite profile of Lactococcus lactis DSM20175 were investigated using transcriptomic and untargeted metabolomic approaches. Real-time growth monitoring combined with flow cytometric cell enumeration showed that β-1,3-glucan supplementation significantly increased both growth rate and final cell density compared with a control group that did not receive any supplementation. Transcriptomic analysis showed a broad downregulation of genes associated with carbon catabolite repression, Rgg/GadR/MutR-family regulators, surface proteins, and membrane transporters, likely indicating an earlier transition from exponential to stationary phase physiology. Untargeted metabolomics revealed extensive differential extracellular metabolite secretion, including shared increases in signature metabolites of fermentation, as well as β-glucan-specific elevation of aromatic and tryptophan-derived metabolites. These multi-omics data revealed that the β-1,3-glucan from E. gracilis functions as a growth substrate, accelerating the growth-phase transition and reshaping metabolic pathways of L. lactis DSM20175. This baseline information has potential implications for synbiotic formulation and industrial fermentation processes.