Fig. 3

The tri-stable-switch circuit helped mice recover from the pH drop caused by excess lactose intake. a Five groups of mice: (1) initial set (n = 4), (2) untreated group (n = 20), (3) model group (n = 20), (4) control group (n = 20), and (5) test group (n = 20) were subjected to different operations in the first week. Mice in the control group and the test group were administrated with bacteria (BL21: pETDuet1-0 in the Control group, BL21: pETDuet1-1 in the test group; OD₆₀₀ = 1) in a total volume of 0.3 mL of a 0.9% normal saline (NS) suspension daily. The other groups were administrated daily with the same volume of 0.9% NS. At the time point of 0 h, mice in the initial set were euthanized for pH measurements. The mice of the model, control, and test group were administrated the lactose solution (12 mg of lactose per 20 g of body weight), and the mice of the untreated group were administrated the same volume of 0.9% NS. During the following 6 h, four mice from each group were euthanized at each time point for pH measurements. b The pH variation (mean ± S.D.) of the mouse colons during 6 h. The initial set is designated as the initial point of four other groups. The pH variation of different groups is colored differently. The pH variation of the model and control group is statistically significant (P < 0.05, Student’s t test, Additional file 1: Table S6). c Four groups of mice: (1) untreated group (n = 20), (2) model group (n = 20), (3) control group (n = 20), and (4) test group (n = 20) were subjected to different operations in the first week, as described in a. Before the time point of 0 h, mice of all the groups were stimulated to defecate for measurements of β-galactosidase activity. At the time point of 0 h, mice of the model, control, and test group were administrated the lactose solution (12 mg of lactose per 20 g of body weight), and mice of the untreated group were administrated the same volume of 0.9% NS. At the time point of 3 h, mice of all the groups were stimulated to defecate for measurements of β-galactosidase activity. d The β-galactosidase activity variation (mean ± S.D.) of the mouse feces during 6 h. The variation of different groups is colored differently. * P < 0.05, ** P < 0.01; n.s., not significant. Student’s t test