Fig. 3: Arginine is sufficient to induce mucoidy in K. pneumoniae and requires the ArgR regulator.

A, B Wild-type (WT) KPPR1 was cultured overnight in low-iron M9 medium supplemented with 18 amino acids (All), 20 mM glycerol (Glyc), or increasing concentrations of arginine (0.025%–0.2%) and 20 mM Glyc. C, D Additionally, KPPR1, astA::kan, argG::kan, and ∆argR mutants were cultured overnight in low-iron M9 minimal media under the following conditions: with 18 amino acids (All), without arginine (-Arg), with 20 mM glycerol (Glyc), or with 20 mM glycerol and 0.2% arginine (Glyc+Arg). (E, F) The strains KPPR1 and ∆argR were transformed with either the empty vector (EV) or argR vector (pargR) and cultured overnight in low-iron minimal M9+All medium. A−E Mucoidy was determined for each of the conditions by sedimenting 0.5 OD₆₀₀ unit of culture at 1000 x g for 5 min and then measuring the supernatant OD₆₀₀. B−F The total capsule abundance was determined by measuring the uronic acid content of crude CPS extracts and normalized to 10⁹ CFUs. Data presented are the mean, and error bars represent the standard error of the mean. In panels (C, D) the cross (†) indicates no growth. A−F Statistical significance was determined using one-way ANOVA with a Dunnett post-test. C, D Statistical significance was determined using two-way ANOVA with a Tukey post-test. The statistics indicated above the data bars represent values relative to M9 + All (A, B) or WT in the same culture condition (C−F). p-values are displayed above each comparison; * p < 0.05; # p < 0.0001. Exact P-values: (A) left to right: <0.0001, <0.0001, <0.0001, 0.0135; (C) left to right: <0.0001, <0.0001, <0.0001, <0.0001; (E) left to right: <0.0001. Experiments were performed 3 independent times, each in biological triplicate (for graphs A,C-F, n = 9 and for graph B, n = 9 for M9 + All, M9+Glyc, and 0.2% arginine conditions, but n = 12 for 0.025%-0.1% arginine conditions). Source data are provided as a Source Data file.