pH-dependent metabolic reprogramming underlying sublethal injury in Lactiplantibacillus plantarum CP039121

This study aimed to characterize SLI in Lactiplantibacillus plantarum CP039121 by directly comparing the sublethal group (PCA) with the control group (MRS) across three pH conditions (3.5, 5.5, and 7.5). The results showed that, SLI rates of L . plantarum CP039121were significantly (P < 0.05) higher (>30%) at pH 3.5 and 7.5 than at pH 5.5 (<3%). Compared with the MRS, PCA treatment resulted in the systemic suppression of the tricarboxylic acid cycle, evidenced by significantly reduced levels of citric acid, isocitric acid, and 2-oxobutanoic acid (P<0.05). Carbohydrate metabolism exhibited a divergence characterized by the significant accumulation of D-glucose (P<0.05) concomitant with the depletion of oligosaccharides, including sucrose, cellobiose, and trehalose (P<0.05). Regarding cellular structure, peptidoglycan precursors such as N-succinyl-L,L-2,6-diaminopimelate were significantly downregulated (P<0.05). Conversely, intracellular buffering agents and salvage metabolites, specifically spermidine, 2-aminoadipic acid, and inosine, were significantly upregulated (P<0.05). The pH 5.5 (409 differentially expressed genes) exhibited upregulation of translation and membrane transport-associated genes, whereas the pH 3.5 (542 differential metabolites) showed global downregulation of ATP-binding cassette transporters. Collectively, these data indicate that SLI entails the inhibition of central metabolic flux and membrane permeability accompanied by the accumulation of intracellular protectants rather than cell wall fortification.