Fig. 1.

Growth study of Strep. mutans. Strep. mutans wild-type, UA159 (▪), BrpB-deficient mutant, JB409 (○), BrpB-complemented strain, JB409C (•), BrpB- and BrpA-deficient double mutant, JB819 (Δ), and BrpB- and BrpA-complemented strain, JB819C (▴), were grown in BHI adjusted to pH 7.5 (a) and pH 6.5 (b) in a Bioscreen C at 37 °C with a sterile mineral oil overlay (50 µl), and the optical density of the cultures was continuously monitored at 600 nm. Results showed that BrpB deficiency in JB409 greatly affects bacterial cell growth. Interestingly, the BrpB and BrpA double deficiency in JB819 partially alleviated the slow growth phenotype of the BrpB-deficient mutant, JB409. During growth in BHI adjusted to pH 6.5, the complemented strain, JB819C, showed an extremely delayed lag phase, when compared to the wild-type and the parent strain, JB819. The data presented here are representative of three independent experiments. The lag phase duration and the doubling time of each strain under the conditions tested are expressed as means and presented in the tables to the right of the growth curves.