Increasing the cellular (pp)pGpp level is associated with activation of stress response genes in Staphylococcus aureus

The stringent response is characterized by the synthesis of the messenger molecules pppGpp, ppGpp or pGpp (collectively designated (pp)pGpp). The phenotypic consequences resulting from (pp)pGpp accumulation vary among species and can be mediated by different underlying mechanisms. Most genome-wide analyses were performed under stress conditions, which often mask the immediate effects of (pp)pGpp mediated regulatory circuits. In Staphylococcus aureus (pp)pGpp can be synthesized via the RelA-SpoT- homologue (RSHSau) upon amino-acid limitation or via one of the two small (p)ppGpp synthetases RelP or RelQ upon cell-wall stress. We used RNA-seq to compare global effects in response to transcriptional induction of the synthetase domain of RSH (RSH- Syn) or RelQ without the need to apply additional stress conditions. We found a significant upregulation of iron and oxidative stress genes. Simultanously, virulence genes psms were upregulated independ of the its regulator Agr. Based and these RNA-Seq results we created mutants of the regulators PerR, Fur and SarA which are associated with the regulation of oxidative stress and iron Overall design: We compared the trascriptional downstream effects of (pp)pGpp by transcriptional induction of RSH-Syn and RelQ by RNA Seq, triplicates, Illumina Next Seq 500 system,