Interpreting glycine-associated phenotypes in Lactiplantibacillus plantarum: the need for strain-specific and medium-controlled evidence.

Han et al. report that glycine supplementation alters growth-associated readouts and improves bile and osmotic stress tolerance in Lactiplantibacillus plantarum KCCM 11322. We agree that these phenotypes may be relevant to starter-culture optimization, but the mechanistic attribution to metabolic remodeling remains incomplete. Pathway inference was based on a reference L. plantarum annotation rather than the KCCM 11322 genome; experiments used chemically undefined MRS, so 0 mM denotes no added glycine rather than a glycine-free baseline; and pH was not systematically controlled. The divergence between visible biomass, OD600, and CFU at high glycine concentrations further emphasizes the need to separate biomass accumulation from viable growth. Strain-specific genomics, defined-medium experiments, pH-matched controls, and targeted metabolic measurements would clarify whether glycine acts as a nutrient, physicochemical modifier, or regulator of metabolic flux.