Arginine Biosynthesis in Staphylococcus aureus

Staphylococcus aureus causes a wide variety of infections including osteomyelitis, endocarditis, and necrotizing pneumonia. It has been known for decades that S. aureus is auxotrophic for many amino acids including arginine. However, we discovered that after extended incubation, S. aureus can be trained to grow in a defined media lacking arginine. We demonstrate here that this delayed growth is due to the selection of mutations in ahrC, a transcriptional regulator of arginine biosynthesis. A mutation in ahrC mediates the growth of S. aureus in CDM-R by facilitating the biosynthesis of arginine via proline. Mutations in putA and argGH halt the growth of the JE2 ahrC mutant while a mutation in argDCJB did not. In addition, Liquid Chromatography with tandem mass spectrometry (LC-MS/MS) analysis showed that 13C5-labelled arginine was detected in the JE2 ahrC mutant when grown in the presence of 13C5-labelled proline and not of13C5-labelled glutamate further confirming that proline is the precursor of arginine. Furthermore, our transcriptional analysis results demonstrate that AhrC in S. aureus functions to primarily repress argGH and arcB1 allowing for arginine biosynthesis via proline. Although the mechanism of arginine biosynthesis regulation was shown to be conserved among species, our data demonstrate that AhrC in S. aureus functions to regulate arginine biosynthesis differently, with the biosynthesis being mediated through the urea cycle using proline as a precursor instead of the highly conserved and well-characterized glutamate pathway which was shown to be inactive in-vitro