CodY in Staphylococcus aureus: regulatory link between metabolism and virulence gene expression

CodY is a conserved regulator in gram-positive organisms described to repress metabolic genes mainly involved in nitrogen metabolism but also to control the expression of virulence genes in pathogens. We constructed codY gene-replacement mutants in three unrelated S. aureus strains (Newman, UAMS-1, RN1HG). codY mutants grew slower in a chemically defined medium compared to the wild type strains. However, only codY mutants were able to grow in medium lacking threonine. Excess of isoleucine resulted in growth inhibition in the wild type but not in the codY mutants indicating a role of isoleucine for CodY dependent repression of metabolic genes. The prototypic CodY-repressed operon ilvDBCleuABCilvA is preceded by a CodY-binding motif and repressed after up-shift with isoleucine and to a lesser extent guanidine. Transcription of the quorum sensing system agr followed a similar expression pattern. The codY dependent repression of agr is in line with the concomitant influence of CodY on typical agr regulated genes such as cap, spa fnbA and coa. However, transcriptional analysis revealed that most of these virulence genes (e.g. cap, fnbA, spa hla) are also regulated by CodY in an agr negative background. Microarray analysis revealed the large majority of codY-repressed genes are involved in amino-acid transport and metabolism, genes showing codY dependent activation were mainly involved in nucleotide transport and metabolism or virulence. In summary, CodY in S. aureus not only acts as repressor for genes involved in nitrogen metabolism but also contributes to virulence gene regulation by supporting as well as substituting agr function. The microarray was manufactured by in situ synthesis of 10'807 long oligonucleotide probes , selected as previously described (Charbonnier, 2005). It covers >98% of all ORFs annotated in strains N315 and Mu50 , MW2, COL , NCTC8325, USA300 , MRSA252 an MSSA476 including their respective plasmids.