Figure 1.

Figure 1.

(p)ppGpp⁰  Staphylococcus aureus displays attenuated virulence in a systemic infection model. A, Schematic overview of the (p)ppGpp turnover enzymes in S. aureus. (p)ppGpp is produced by 3 enzymes, Rel, RelP, and RelQ via the SYN domain. Rel is also capable of hydrolyzing (p)ppGpp via the HD domain. Interactions between Rel and the ribosome occur via the CT domain and allow amino acid starvation to be sensed. S. aureus was injected into the yolk sac circulation valley of zebrafish embryos at 30 hpf. B and C, Survival of zebrafish larvae injected with S. aureus WT or (p)ppGpp⁰ grown to (B) exponential and (C) stationary phase. Doses of 3000–4000 colony-forming units of each strain were injected into the yolk sac circulation valley at 30 hpf to initiate a bloodstream infection. Survival was monitored until 93 hpi when the larvae reached 5.2 days postfertilization. Pairwise comparisons (log-rank [Mantel-Cox] test) were (B) (p)ppGpp⁰ versus WT, ****P < .0001; and (C) (p)ppGpp⁰ versus WT, **P = .0048. Experiments were performed in quadruplicate (B) and triplicate (C). Abbreviations: (p)ppGpp, guanosine tetraphosphate/guanosine pentaphosphate; (p)ppGpp⁰, (p)ppGpp null mutant; CT, C-terminal; hpf, hours postfertilization; HD, hydrolase; hpi, hours postinfection; SYN, synthetase; WT, wild type.