Staphylococcus aureus Does Not Synthesize Arginine from Proline under Physiological Conditions

Area of Science:

• Microbiology
• Biochemistry
• Metabolic Regulation

Background:

• Staphylococcus aureus, a Gram-positive pathogen, possesses genes for both arginine-proline interconversion and the glutamate pathway for arginine synthesis.
• Carbon catabolite repression (CCR) by CcpA typically represses arginine synthesis, leading to the assumption that CCR causes arginine auxotrophy in S. aureus.

Purpose of the Study:

• To investigate the actual cause of arginine auxotrophy in Staphylococcus aureus.
• To determine whether CCR or other metabolic factors limit arginine synthesis from proline.

Main Methods:

• Manipulating pyrroline-5-carboxylate (P5C) levels through PutA overexpression and proC deletion.
• Assessing arginine synthesis and bacterial growth under various carbon sources and genetic modifications.
• Evaluating the role of the glutamate pathway by ectopic expression of its enzymes.
• Conducting animal experiments to assess the in vivo requirement of the arginine-proline interconversion pathway.

Main Results:

• Arginine auxotrophy in S. aureus is not caused by CCR but by insufficient intracellular pyrroline-5-carboxylate (P5C) levels.
• P5C levels are limited by its consumption by ProC, even when proline dehydrogenase (PutA) is induced.
• Overexpressing PutA or deleting proC restored arginine synthesis from proline, irrespective of the carbon source.
• Ectopic expression of glutamate pathway enzymes rendered S. aureus arginine prototrophic.
• The arginine-proline interconversion pathway is dispensable for S. aureus survival in animal models.

Conclusions:

• Staphylococcus aureus does not synthesize arginine from proline under physiological conditions.
• Arginine auxotrophy in S. aureus is attributed to the inactivity of the conserved glutamate pathway, not CcpA-mediated CCR.
• These findings challenge the established understanding of arginine metabolism in S. aureus.