Figure 2.

Deletion of phoU2 leads to a lower growth yield and increased β-lactam antibiotic sensitivity that are reversed by a Δpst2 mutation. (A) Representative growth curves in BHI broth (≈18 mM P_i) of encapsulated parent strain (IU1781), a ΔphoU2 mutant (IU6375), and a ΔphoU2 mutant complemented by ectopic expression of PhoU2⁺ (IU6397). Strains were grown as described in Materials and Methods. A linear scale for OD₆₂₀ is used to emphasize differences in growth yields. Growth yields and rates are quantitated for multiple determinations in Table S4. (B) Cefotaxime sensitivity assays of encapsulated parent strain (IU1781), a ΔphoU2 mutant (IU6375), and a PhoU2⁺-complemented ΔphoU2 mutant (IU6397). Cefotaxime disk sensitivity assays of bacteria grown in BHI broth were performed as described in Material and Methods. P-values were calculated by unpaired t-tests relative to the parent strain using GraphPad Prism; (n ≥ 3); ^***P < 0.001. Increased sensitivity to other β-lactam antibiotics, vancomycin, gentamicin, and tetracycline of a ΔphoU2 mutant compared to its isogenic parent strain is shown in Table S5. (C) Representative growth curves of encapsulated parent strain (IU1781) and ΔphoU2 (IU6375), Δpst2-phoU2 (IU6550), and Δpst2 (IU6610) mutants in BHI broth. (D) Cefotaxime sensitivity assays for encapsulated parent strain (IU1781), and ΔphoU2 (IU6375), Δpst2-phoU2 (IU6550), and Δpst2 (IU6610) mutants. (n ≥ 3); ^***P < 0.001.