Figure 6.

So-AqpA promotes the oxic growth and intraspecies and interspecies competitive advantage of S. oligofermentans. A, growth profiles were determined for the WT strain, So-aqpA mutant (ΔaqpA), So-aqpA complemented (aqpAcom), and the Phe-40 substitution complemented (aqpAF40Acom) strains that were statically cultured in 10 ml or 40 ml BHI broth. Overnight BHI cultures of the tested strains were 1:30 inoculated into fresh BHI medium and incubated at 37 °C, and OD₆₀₀ was measured at the indicated time. The results are expressed as averages ± S.D. of three independent experiments. Suffix numbers after strain names indicate the culture volumes. B, exponential growing cells from the cultures above were collected, and HyPer fluorescence was observed and measured using the same procedure as described in Fig. 2. Representative images of three independent experiments are shown and fluorescence intensity a.u. per ROI is shown inside the parentheses in each image. Bar, 5 μm. C, competition between the wild strain and So-aqpA mutant was determined for three successive subcultured generations under high oxygen content. The same amounts of the two strains were co-inoculated or mono-inoculated into 10 ml BHI broth contained in a 100-ml flask, and the co-culture and mono-culture were subcultured for three successive generations. Colony-forming units (cfu) of each culture in each generation were counted on BHI agar plate; BHI plate containing 1 mg/ml kanamycin was used to count cfu of the ΔaqpA mutant in co-cultures. The results are averages ± S.D. of three independent experiments. *, significantly different from the So-aqpA deletion mutant in the first generation of co-culture as verified by one-way ANOVA analysis followed by Tukey's post hoc test (p <0.05). D, growth suppression of S. mutans (Sm) by the S. oligofermentans WT strain and So-aqpA mutant (ΔaqpA) was tested on TPYG plate (0.5% tryptone, 0.5% peptone, 1% yeast, 1% glucose, 4% salt solution) (23). Overnight cultures of the tested strains were collected and adjusted to the same OD₆₀₀. 10 μl of each strain were spotted side-by-side on the plates and incubated at 37 °C in the candle jar for 24 h. The experiments were repeated three times, and one representative experiment is shown.