Defining the transcriptional adaptation of Staphylococcus aureus to a range of nutritional sulfur supplementation

Bacterial pathogens must adapt to dynamic host tissue environments to proliferate. Accordingly, elegant regulatory systems evolved to overcome challenges presented by the host and satisfy nutritional requirements. Sulfur is an essential macronutrient and Gram-positive bacteria such as Staphylococcus aureus balance this nutritional requirement by employing the transcriptional repressor, CymR. Previous investigations defined the S. aureus CymR regulon by comparing transcripts generated in a cymR mutant cultured in cystine replete, rich medium to wild type cells. This study defines the S. aureus CymR-dependent and -independent sulfur-starvation response in chemically defined growth conditions. Results demonstrate that the sulfur starvation and sulfur replete CymR regulons exhibit considerable overlap, including previously noted connections between iron acquisition, oxidative stress, and sulfur metabolism. The link between iron acquisition, oxidative stress, and sulfur metabolism is validated further by the finding that sulfur-containing glutathione (GSH) mitigates heme and peroxide toxicity. In addition to GSH, Cys and thiosulfate fulfill the S. aureus sulfur requirement. Transcriptional responses to organic (cysteine, cystine, reduced and oxidized GSH) or inorganic thiosulfate were quantified, revealing sulfur source-specific expression patterns. Thiosulfate induced the largest number of differentially expressed genes. Consequently, the thiosulfate transporter (SAUSA300_RS10985) has been confirmed as essential for S. aureus growth when thiosulfate is the sulfur source. Furthermore, we demonstrate that a hypothetical protein operonic with SAUSA300_RS10985, SAUSA300_RS10980, supports maximal growth on thiosulfate. Collectively, a resourceful transcriptomics framework is provided which underscores the dynamic nature of S. aureus sulfur metabolism.