Proline biosynthesis regulates proline transport in Staphylococcus aureus.

Staphylococcus aureus is metabolically diverse with the ability to rapidly adapt to a vast array of nutrient sources. This allows the pathogen to colonize a variety of niches in the host. For instance, S. aureus is the leading cause of skin and soft tissue infections, a niche that has been shown to become glucose-depleted over the course of an infection. Previous studies have shown that in niches where glucose is deficient, S. aureus utilizes peptides and free amino acids as nutrient sources. Primarily, these amino acids include glutamate and amino acids that can serve as substrates for glutamate synthesis. While arginine and histidine serve as substrates in glutamate synthesis, proline is the primary source of glutamate. Indeed, S. aureus utilizes proline as a secondary carbon source only when glucose is absent, and it can be synthesized from arginine or acquired via proline transporters from its environment. Although S. aureus encodes two putative pathways for proline biosynthesis, it has been shown that pyrroline-5-carboxylate reductase (encoded by proC) is the sole proline biosynthetic pathway in S. aureus. Studies from our laboratory have revealed that despite encoding five putative proline transporters (B7H15_03660, opuC, opuD, proP, putP), only two of the transporters, PutP and B7H15_03660 are responsible for a majority of proline transport under the laboratory conditions tested. Surprisingly, when we introduced the proC mutation into the B7H15_03660 putP double mutant, we observed proline-dependent growth, even though the primary proline transporters and proline biosynthetic pathway were knocked-out. In contrast, a transporter null ΔproC strain was unable to grow. These data suggest that inhibiting proline biosynthesis alters proline transport, and therefore one or more of the additional transporters, OpuC, OpuD, and/or ProP, are activated under these conditions. After introducing opuC, opuD, and/or proP mutations into the Δ03660 ΔputP ΔproC strain, we found that both OpuC and ProP are important for proline transport. Additionally, we observed proline-dependent growth in a proline transporter null ΔproC strain when high amounts of exogenous proline are added to the media. This growth appears to be due to an acquired mutation and will be studied more in the future. Overall these studies have revealed that proline transport is tightly linked to proline biosynthesis.https://digitalcommons.unmc.edu/surp2021/1021/thumbnail.jp