GSE110170
Examining the role of mupirocin-induced nutritional stress in the S. aureus stringent stress response
The stringent response is a conserved stress response employed by various bacteria to respond to and cope with conditions of amino acid starvation, carbon-source, fatty acid, oxygen/iron limitation, heat shock, antimicrobial challenge, and/or other environmental stressors. In S. aureus, the stringent response is mediated in part by enzyme RSH (relA spoT homologue) which synthesizes two nucleotide-based molecules, guanosine tetraphosphate (ppGpp) and pentaphosphate (pppGpp), collectively known as (p) ppGpp. This response is known to result in a number of diverse physiological and metabolic changes which we further characterized in the present study. Specifically, the global transcriptome of the RSH synthase mutant (rshsyn) was compared to the WT parent S. aureus strain (NCTC 8325) by RNA-Seq analysis under both normal and nutrient-limited media conditions. In order to mimic nutrient limitation, bacteria were treated with mupirocin, an antibiotic and isoleucine analogue known to lead to isoleucine starvation. In the WT strain, in response to mupirocin-induced isoleucine starvation, genes encoding protein synthesis machinery were suppressed while genes encoding amino acid biosynthetic machinery were upregulated. This response likely employed to compensate for amino acid deprivation, was not induced in the stringent response mutant. Furthermore, under starvation conditions, biofilm-related genes (i.e. icaA, icaC, fnbA, clfB, emp) were more upregulated in the WT than the stringent response mutant. Moreover, the effect of mupirocin caused a stronger upregulation of several proteases (i.e. sspA, sspP, sppB, aur), lipases (lip, geh) and phenol soluble modulin toxins in the WT as compared to the mutant. Overall, these results suggest that under starvation conditions, RSH plays an important role in helping the cell respond to nutritional stress as well as regulates the expression of numerous colonization and virulence factors. Overall design: RNA-Seq profiling of gene expression in Staphylococcus aureus subsp. aureus NCTC8325 with two genotypes grown in two conditions