ABSTRACTIsoprenoids are a class of ubiquitous organic molecules synthesized from the five-carbon starter unit isopentenyl pyrophosphate (IPP). Comprising more than 30,000 known natural products, isoprenoids serve various important biological functions in many organisms. In bacteria, undecaprenyl pyrophosphate is absolutely required for the formation of cell wall peptidoglycan and other cell surface structures, while ubiquinones and menaquinones, both containing an essential prenyl moiety, are key electron carriers in respiratory energy generation. There is scant knowledge on the nature and regulation of bacterial isoprenoid pathways. In order to explore the cellular responses to perturbations in the mevalonate pathway, responsible for producing the isoprenoid precursor IPP in many gram-positive bacteria and eukaryotes, we constructed three strains ofStaphylococcus aureusin which each of the mevalonate pathway genes is regulated by an IPTG (isopropyl-β-d-thiogalactopyranoside)-inducible promoter. We used DNA microarrays to profile the transcriptional effects of downregulating the components of the mevalonate pathway inS. aureusand demonstrate that decreased expression of the mevalonate pathway leads to widespread downregulation of primary metabolism genes, an upregulation in virulence factors and cell wall biosynthetic determinants, and surprisingly little compensatory expression in other isoprenoid biosynthetic genes. We subsequently correlate these transcriptional changes with downstream metabolic consequences.