CcpA Mediates Proline Auxotrophy and Is Required forStaphylococcus aureusPathogenesis

Abstract

Human clinical isolates of Staphylococcus aureus, for example, strains Newman and N315, cannot grow in the absence of proline, albeit their sequenced genomes harbor genes for two redundant proline synthesis pathways. We show here that under selective pressure, S. aureus Newman generates proline-prototrophic variants at a frequency of 3 x 10(-6), introducing frameshift and missense mutations in ccpA or IS1811 insertions in ptsH, two regulatory genes that carry out carbon catabolite repression (CCR) in staphylococci and other Gram-positive bacteria. S. aureus Newman variants with mutations in rocF (arginase), rocD (ornithine aminotransferase), and proC (Delta(1)-pyrroline 5-carboxylate [P5C] reductase) are unable to generate proline-prototrophic variants, whereas a variant with a mutation in ocd (ornithine cyclodeaminase) is unaffected. Transposon insertion in ccpA also restored proline prototrophy. CcpA was shown to repress transcription of rocF and rocD, encoding the first two enzymes, but not of proC, encoding the third and final enzyme in the P5C reductase pathway. CcpA bound to the upstream regions of rocF and rocD but not to that of proC. CcpA's binding to the upstream regions was greatly enhanced by phosphorylated HPr. The CCR-mediated proline auxotrophy was lifted when nonpreferred carbohydrates were used as the sole carbon source. The ccpA mutant displayed reduced staphylococcal load and replication in a murine model of staphylococcal abscess formation, indicating that carbon catabolite repression presents an important pathogenesis strategy of S. aureus infections.