Survival of various mutants to polymyxin.

<p>Wild type and various mutants in genes involved in resistance to AMP (<i>phoP</i>, <i>pmrA</i>, <i>dltB</i>, <i>arnB</i>) were incubated in the presence of 1 µg ml⁻¹ polymyxin for 1 h. Samples were diluted and plated on LB agar plates to assess bacterial viability. Survival values are relative to the original inoculum. Data correspond to mean values of three independent experiments.</p

Survival of pea aphids after oral infection by wt and mutants of <i>D. dadantii</i> 3937.

<p>Survival is shown for aphids treated with wt bacteria (red), <i>arnB</i> (green), <i>dltB</i> (blue), and <i>dltB arnB</i> (brown) mutants. Results were obtained with 2×30 third instar aphid nymphs per treatment, including a diet-treated control (no mortality, not shown). The experiment was repeated twice with very similar results (p<0.06 in all comparisons of wt with <i>arnB</i> mutants). Median survival times (LT50s) were calculated with a Weibull fit (inlet), and give the following series [95% confidence intervals]: wt, 2.92 [2.18–3.92]; <i>arnB</i>, 4.74 [3.42–6.55]; <i>dltB</i> 3.58 [2.62–4.88] and <i>arnB</i>-<i>dltB</i> double mutant, 4.46 [3.23–6.18].</p

Regulation of <i>arnB</i>.

<p>The <i>arnB-uidA</i> fusion of strain A5256 was assayed in the presence of increasing concentrations of polymyxin (A), protamine (B), and Mg²⁺ (C). Effect of <i>phoP</i> and <i>pmrA</i> mutations on <i>arnB-uidA</i> regulation by Mg²⁺ (D) and protamine (E) was assayed. Cultures were performed in LB medium for A, C and D and in M63 medium for B and E since protamine precipitates in LB medium. Activities are the mean value from at least four separate experiments and are expressed in µmoles of <i>p</i>-nitrophenol produced per minute and per milligram of bacterial dry weight ± standard deviation.</p

A subset of <i>D. dadantii</i> genes whose expression varies in aphid.

a<p>Positive values represent genes upregulated in aphids, whereas negative values represent genes downregulated.</p

Regulation of <i>sstE</i> and <i>outC</i>.

<p>The <i>sttE-uidA</i> and <i>outC-uidA</i> fusions of strain A4206 and A1919, respectively, were assayed in the presence of 5 µg/ml of polymyxin or 10 mg/ml Mg²⁺ in the wt, <i>phoP</i> and <i>pmrA</i> backgrounds. Activities are the mean value from at least four separate experiments and are expressed in µmoles of <i>p</i>-nitrophenol produced per minute and per milligram of bacterial dry weight ± standard deviation.</p