SroA links SigS-dependent stress signaling to metabolic remodeling in Staphylococcus aureus

Staphylococcus aureus encounters diverse environmental conditions during colonization and infection, including fluctuations in nutrient availability, oxidative stress, and oxygen limitation. Adaptation to these environments requires regulatory systems that coordinate stress responses with metabolic remodeling. The extracytoplasmic function sigma factor SigS contributes to stress adaptation and virulence in S. aureus and directly activates expression of the sroAB operon, which encodes the small proteins SroA and SroB. While previous work demonstrated that SroA participates in feedback regulation of sigS expression, the broader physiological role of SroA has remained unclear. To define the regulatory functions of SroA, we performed RNA sequencing following inducible overexpression of sroA in S. aureus. Transcriptome analysis revealed extensive remodeling of gene expression, with approximately 200 transcripts significantly altered. Transcriptome analysis revealed coordinated repression of metabolic pathways (including nitrate respiration and nucleotide biosynthesis) alongside activation of stress-response and nutrient acquisition genes. Northern blot and quantitative RT-PCR analysis confirmed repression of narG and narJ transcripts following SroA overexpression. Consistent with these transcriptional changes, nitrate reduction assays demonstrated that SroA overexpression reduces nitrate respiration activity. In addition to repression of nitrate respiration genes, SroA overexpression broadly suppressed genes involved in de novo purine and pyrimidine biosynthesis. In contrast, transcripts associated with stress responses and nutrient acquisition, including the SOS-associated gene sosA and the phosphate transport gene pstS, were upregulated. Together, these findings identify SroA as a regulator that links stress-responsive signaling to metabolic remodeling in S. aureus, particularly through modulation of nitrate respiration pathways.