FIG 4.
PpnN does not confer complement resistance by contributing to cell wall biogenesis. (A) Model showing (p)ppGpp-mediated regulation of ppnN. PpnN produces free nucleobases and ribose 5′-phosphate (R5P), the latter of which could enter the pentose phosphate pathway and regulate carbon metabolism. (B) MIC of ampicillin, ciprofloxacin, rifampin, and colistin for wild-type S. Typhimurium strain SL1344 and ΔppnN and ΔrelA ΔspoT mutants. The ΔppnN mutant does not show increased susceptibility to any of the tested antibiotics relative to wild-type S. Typhimurium, whereas the ΔrelA ΔspoT mutant is 8-fold more susceptible to colistin. Data are representative of three replicates. (C) LPS analysis of the ΔrelA ΔspoT and ΔppnN mutants compared to wild-type S. Typhimurium. The ΔrelA ΔspoT mutant expresses significantly lower levels of very long and long O-antigen, whereas the LPS O-antigen of the ΔppnN mutant is similar to that of the wild-type strain. Data are representative of two replicates. Strains carry the empty pGEN-MCS vector control unless otherwise specified. Transcriptional reporter of the full-length wzy promoter (D) and wzzST promoter (E) showed (p)ppGpp-dependent up-regulation. Data are the means ± SEM (error bars) from three independent experiments. Strains are carrying the empty pWSK129 vector control unless otherwise specified. ns, not significant; *, P < 0.05; ***, P < 0.0001.