Investigating the genetic regulation of the ECF sigma factor σS in Staphylococcus aureus

Abstract

BackgroundWe previously identified an ECF sigma factor, σS, that is important in the stress and virulence response of Staphylococcus aureus. Transcriptional profiling of sigS revealed that it is differentially expressed in many laboratory and clinical isolates, suggesting the existence of regulatory networks that modulates its expression.ResultsTo identify regulators of sigS, we performed a pull down assay using S. aureus lysates and the sigS promoter. Through this we identified CymR as a negative effector of sigS expression. Electrophoretic mobility shift assays (EMSAs) revealed that CymR directly binds to the sigS promoter and negatively effects transcription. To more globally explore genetic regulation of sigS, a Tn551 transposon screen was performed, and identified insertions in genes that are involved in amino acid biosynthesis, DNA replication, recombination and repair pathways, and transcriptional regulators. In efforts to identify gain of function mutations, methyl nitro-nitrosoguanidine mutagenesis was performed on a sigS-lacZ reporter fusion strain. From this a number of clones displaying sigS upregulation were subject to whole genome sequencing, leading to the identification of the lactose phosphotransferase repressor, lacR, and the membrane histidine kinase, kdpD, as central regulators of sigS expression. Again using EMSAs we determined that LacR is an indirect regulator of sigS expression, while the response regulator, KdpE, directly binds to the promoter region of sigS.ConclusionsCollectively, our work suggests a complex regulatory network exists in S. aureus that modulates expression of the ECF sigma factor, σS.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-014-0280-9) contains supplementary material, which is available to authorized users.

Revealing 29 sets of independently modulated genes in Staphylococcus aureus , their regulators, and role in key physiological response

“…4 B ). Previous studies have shown that CymR represses sigS expression and therefore may lead to its decreased activity ( 42 ). We confirmed this relationship as the SigS i-modulon activity was anticorrelated with the CymR i-modulon activity (Pearson R = −0.68, P = 8.23e-10) ( SI Appendix , Fig.…”

Assessment of Bona Fide sRNAs in Staphylococcus aureus

“…Transcription in S. aureus depends on four sigma (σ) factors: σ A , the primary σ factor responsible for the transcription of most genes, σ B , involved in the general stress response, σ H , implicated in the competence state but cryptic in NCTC8325 (Morikawa et al, 2012 ), and σ S , the extracytoplasmic function sigma factor (Burda et al, 2014 ).…”

Revealing 29 sets of independently modulated genes in Staphylococcus aureus, their regulators and role in key physiological responses

“…As with the SigB i-modulon, expression of the sigS gene correlated to activity of the ICA-derived SigS i-modulon (Pearson R = 0.77, p-value = 4.26e-22) ( Figure 4a ). Previous studies have shown that CymR represses sigS expression and therefore may lead to its decreased activity 41 . We confirmed this relationship as the SigS i-modulon activity was anti-correlated with the CymR i-modulon activity (Pearson R = -0.68, p-value = 8.23e-10) ( Figure S4c ).…”