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

Abstract

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 physiology. 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. Previous work demonstrated that SroA participates in feedback regulation of sigS expression, but the broader physiological role of SroA has remained unclear. To further define the regulatory functions of SroA, we performed RNA sequencing following inducible overexpression of sroA in S. aureus. Transcriptome analysis identified altered expression of genes associated with nitrate respiration, nucleotide biosynthesis, stress responses, and nutrient acquisition. Northern blot and quantitative RT-PCR analysis confirmed repression of narG and narJ transcripts following SroA overexpression. Consistent with these transcriptional changes, SroA overexpression impaired nitrate reduction and produced a modest but significant growth disadvantage under anaerobic conditions in chemically defined medium supplemented with glucose and nitrate. In addition to repression of nitrate respiration genes, SroA overexpression reduced expression of genes involved in de novo purine and pyrimidine biosynthesis, while transcripts associated with stress responses and nutrient acquisition, including sosA and pstS, were increased. Together, these findings support a role for SroA in modulating nitrate respiration-associated pathways and growth under conditions supporting anaerobic respiration, linking SigS-dependent stress signaling to metabolic adaptation in S. aureus.