Amino Acid Catabolism in Staphylococcus aureus and the Function of Carbon Catabolite Repression.

Cortney R Halsey,Marat Sadykov,Robert Powers,Mckenzie K Lehman,Laurey Steinke,Austin S Nuxoll,Shulei Lei,Paul D Fey,Jacqueline K Wax

doi:10.1128/mbio.01434-16

Abstract

ABSTRACTStaphylococcus aureus must rapidly adapt to a variety of carbon and nitrogen sources during invasion of a host. Within a staphylococcal abscess, preferred carbon sources such as glucose are limiting, suggesting that S. aureus survives through the catabolism of secondary carbon sources. S. aureus encodes pathways to catabolize multiple amino acids, including those that generate pyruvate, 2-oxoglutarate, and oxaloacetate. To assess amino acid catabolism, S. aureus JE2 and mutants were grown in complete defined medium containing 18 amino acids but lacking glucose (CDM). A mutation in the gudB gene, coding for glutamate dehydrogenase, which generates 2-oxoglutarate from glutamate, significantly reduced growth in CDM, suggesting that glutamate and those amino acids generating glutamate, particularly proline, serve as the major carbon source in this medium. Nuclear magnetic resonance (NMR) studies confirmed this supposition. Furthermore, a mutation in the ackA gene, coding for acetate kinase, also abrogated growth of JE2 in CDM, suggesting that ATP production from pyruvate-producing amino acids is also critical for growth. In addition, although a functional respiratory chain was absolutely required for growth, the oxygen consumption rate and intracellular ATP concentration were significantly lower during growth in CDM than during growth in glucose-containing media. Finally, transcriptional analyses demonstrated that expression levels of genes coding for the enzymes that synthesize glutamate from proline, arginine, and histidine are repressed by CcpA and carbon catabolite repression. These data show that pathways important for glutamate catabolism or ATP generation via Pta/AckA are important for growth in niches where glucose is not abundant, such as abscesses within skin and soft tissue infections.

Highlights

Staphylococcus aureus must rapidly adapt to a variety of carbon and nitrogen sources during invasion of a host
Our results show that glutamate and amino acids that serve as substrates for glutamate synthesis, proline, function as major carbon sources during growth, whereas other amino acids that generate pyruvate are important for ATP synthesis via substrate-level phosphorylation in the Pta-AckA pathway
To fully assess amino acid catabolism, a complete defined medium was prepared as described by Hussain and colleagues [25] except that no glucose was added

Summary

Introduction

Staphylococcus aureus must rapidly adapt to a variety of carbon and nitrogen sources during invasion of a host. Transcriptional analyses demonstrated that expression levels of genes coding for the enzymes that synthesize glutamate from proline, arginine, and histidine are repressed by CcpA and carbon catabolite repression These data show that pathways important for glutamate catabolism or ATP generation via Pta/AckA are important for growth in niches where glucose is not abundant, such as abscesses within skin and soft tissue infections. We have only begun to study how particular carbon and nitrogen sources that are available to S. aureus in specific host niches affect virulence factor expression and subsequent invasion, metastasis, or quiescence As these metabolic pathways are required for bacterial proliferation within the host, knowledge of these pathways may reveal novel avenues for drug development. Growth under these conditions required peptides to serve as a carbon source to facilitate gluconeogenesis

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