The Staphylococcus aureus genome encodes three ferric uptake regulator (Fur) homologues: Fur, PerR, and Zur. To determine the exact role of PerR, we inactivated the gene by allelic replacement using a kanamycin cassette, creating strain MJH001 (perR). PerR was found to control transcription of the genes encoding the oxidative stress resistance proteins catalase (KatA), alkyl hydroperoxide reductase (AhpCF), bacterioferritin comigratory protein (Bcp), and thioredoxin reductase (TrxB). Furthermore, PerR regulates transcription of the genes encoding the iron storage proteins ferritin (Ftn) and the ferritin-like Dps homologue, MrgA. Transcription of perR was autoregulated, and PerR repressed transcription of the iron homeostasis regulator Fur, which is a positive regulator of catalase expression. PerR functions as a manganese-dependent, transcriptional repressor of the identified regulon. Elevated iron concentrations produced induction of the PerR regulon. PerR may act as a peroxide sensor, since addition of external hydrogen peroxide to 8325-4 (wild type) resulted in increased transcription of most of the PerR regulon, except for fur and perR itself. The PerRregulated katA gene encodes the sole catalase of S. aureus, which is an important starvation survival determinant but is surprisingly not required for pathogenicity in a murine skin abscess model of infection. In contrast, PerR is not necessary for starvation survival but is required for full virulence (P < 0.005) in this model of infection. PerR of S. aureus may act as a redox sentinel protein during infection, analogous to the in vitro activities of OxyR and PerR of Escherichia coli and Bacillus subtilis, respectively. However, it differs in its response to the metal balance within the cell and has the added capability of regulating iron uptake and storage.

An increased dependency on glycolysis for ATP production is considered to be a hallmark of tumor cells. Whether this increase in glycolytic activity is due mainly to inherent metabolic alterations or to the hypoxic microenvironment remains controversial. Here we have transformed human adult mesenchymal stem cells (MSC) using genetic alterations as described for differentiated cells. Our data suggest that MSC require disruption of the same pathways as have been shown for differentiated cells to confer a fully transformed phenotype. Furthermore, we found that MSC are more glycolytic than primary human fibroblasts and, in contrast to differentiated cells, do not depend on increased aerobic glycolysis for ATP production during transformation. These data indicate that aerobic glycolysis (the Warburg effect) is not an intrinsic component of the transformation of adult stem cells, and that oncogenic adaptation to bioenergetic requirements, in some circumstances, may also rely on increases in oxidative phosphorylation. We did find, however, a reversible increase in the transcription of glycolytic enzymes in tumors generated by transformed MSC, indicating this is a secondary phenomenon resulting from adaptation of the tumor to its microenvironment. adult stem cells ͉ glycolysis ͉ Warburg effect

The starvation-survival response of Staphylococcus aureus as a result of glucose, amino acid, phosphate, or multiple-nutrient limitation was investigated. Glucose and multiple-nutrient limitation resulted in the loss of viability of about 99 to 99.9% of the population within 2 days. The remaining surviving cells developed increased survival potential, remaining viable for months. Amino acid or phosphate limitation did not lead to the development of a stable starvation-survival state, and cells became nonculturable within 7 days. For multiple-nutrient limitation, the development of the starvation-survival state was cell density dependent. Starvation survival was associated with a decrease in cell size and increase in resistance to acid shock and oxidative stress. There was no evidence for the formation of a viable but nonculturable state during starvation as demonstrated by flow cytometry. Long-term survival of cells was dependent on cell wall and protein biosynthesis. Analysis of [35S]methionine incorporation and labelled proteins demonstrated that differential protein synthesis occurred deep into starvation.