Fig. 1

Histamine produced by wild type (WT) L. reuteri given variable extracellular a pH or b [chloride]. Cells were cultured in rich media (MRS) for 24 h, prior to washing and resuspension in potassium citrate buffers at a pH 4.5, 5.5, 6.5, or 7.5 with 80 mM sodium chloride and 15 mM l-histidine hydrochloride (95 mM total Cl⁻) or b pH 5.0 with 0, 5, 20 or 80 mM sodium chloride and 15 mM l-histidine hydrochloride (15, 20, 35, or 95 mM total Cl⁻) for 3.5 h. Histamine in cell-free supernatants was measured by LC–MS. Raw histamine concentrations were normalized to the OD₆₀₀ value in MRS obtained for each sample prior to resuspension. N = 4 biological replicates. Error bars represent ± SEM. One way ANOVA with Tukey’s multiple comparison test. *P < 0.05, ***P < 0.001, ****P < 0.0001