| Our goal was to determine the role of the major transcriptional regulator of iron metabolism in Salmonella enterica serotype Tyhphimurium. This regulator, termed Ferric Uptake Regulator or Fur, requires ferrous iron as a cofactor to bind DNA. Fur senses concentrations of intracellular ferrous iron and responds accordingly by binding the operator sites of promoters thereby inhibiting transcription of targeted genes, many encode proteins responsible for iron import. This method of regulation is lost when the cofactor is removed. Therefore, Fur controls iron concentration in the cell. In anaerobically grown Delta fur, 298 genes were differentially expressed, 77 of which were previously identified as being under the control of a major regulator of anaerobiosis, Fumarate Nitrate Reduction or FNR. In general, increased transcription of genes required for iron acquisition/storage, carbohydrate metabolism, electron transport, oxidative/nitrosative stress, and modulators of virulence occurred in Deltafur. Fur regulates transcription of a NO · detoxifying gene, hmpA, and a ferritin-like gene, ftnB, in an apparently indirect manner. In addition, Fur's contribution to the regulation of Salmonella Pathogenicity Island 1 was discovered to be mediated by the derepression of a gene encoding a histone-like protein, hns, in Delta fur. Bioinformatic analysis identified a putative Fur binding site upstream of hns and when the DNA segment containing this putative Fur site was deleted the result was significantly reduced expression of the H-NS repressed hilA in a fur + background. This indicates increased expression of hns leading to reduced expression of hilA. Fur was found essential for virulence in an acute systemic model of Salmonella infection.;Here we also report Fur is required for anaerobic activity of the two heme containing catalases (HPI and HPII) in Salmonella enterica serotype Typhimurium. Data presented indicate partial restoration of HPI and HPII in Deltafur by adding o-amino-levulinic acid, a precursor to heme biosynthesis, to the growth media. However, the addition of L-glutamate, a precursor to o-amino-levulinic acid, was capable of partially restoring only HPI and had no effect on HPII activity. Likewise, supplying fur in trans partially restored HPI and HPII activity. In addition, Fur is required for maintaining anaerobic activity of HPI and HPII activity during H2O2 stress. Deltafur exhibited reduced aerobic growth when grown in the presence of sodium cyanide, an inhibitor of heme containing respiratory enzymes. Therefore, Fur controls heme biosynthesis through modulation of L-glutamate and o-amino-levulinic acid concentrations in the cell by protein abundance or enzyme activity of factors responsible for their synthesis.;Data demonstrates that Fur controls a diverse set of genes and enzymes involved in physiology within the bacterial cell. This signifies the importance of metal homeostasis on the physiological state of the cell. However, the major method of regulation within the cell by Fur is indirect. In this regard, Fur acts as a sensor to controlling many factors which subsequently respond by modifying transcriptional expression, protein function, and/or enzyme activity. This demonstrates that Fur is a bona fide global regulator in Salmonella enterica serotype Typhimurium. |
