Victor Torres - Academia.edu (original) (raw)

Papers by Victor Torres

Cell Host & Microbe, 2007

Staphylococcus aureus, a bacterium responsible for tremendous morbidity and mortality worldwide, ... more Staphylococcus aureus, a bacterium responsible for tremendous morbidity and mortality worldwide, exists as a harmless commensal organism in approximately 25% of the human population. Identifying the molecular machinery that is activated upon infection is central to understanding staphylococcal pathogenesis. We describe here the Heme-Sensor System (HssRS) that responds to heme exposure and activates expression of the Heme Regulated Transporter (HrtAB). The coordinated activities of HssRS and HrtAB maintain intracellular heme homeostasis and modulate S. aureus virulence. Inactivation of the Hss or Hrt systems leads to increased virulence in a vertebrate infection model, a phenotype that is associated with an inhibited innate immune response. Genomic analyses have identified orthologous Hss and Hrt systems in Bacillus anthracis, Listeria monocytogenes, and Enterococcus faecalis, suggesting a conserved regulatory system by which Gram positive pathogens sense heme as a molecular marker of internal host tissue and modulate virulence.

Science, 2008

Bacterial infection often results in the formation of tissue abscesses, which represent the prima... more Bacterial infection often results in the formation of tissue abscesses, which represent the primary site of interaction between invading bacteria and the innate immune system. We identify the host protein calprotectin as a neutrophil-dependent factor expressed inside Staphylococcus aureus abscesses. Neutrophil-derived calprotectin inhibited S. aureus growth through chelation of nutrient Mn2+ and Zn2+: an activity that results in reprogramming of the bacterial transcriptome. The abscesses of mice lacking calprotectin were enriched in metal, and staphylococcal proliferation was enhanced in these metal-rich abscesses. These results demonstrate that calprotectin is a critical factor in the innate immune response to infection and define metal chelation as a strategy for inhibiting microbial growth inside abscessed tissue.

Biometals, 2007

The bacterial pathogen Staphylococcus aureus is responsible for a significant amount of human mor... more The bacterial pathogen Staphylococcus aureus is responsible for a significant amount of human morbidity and mortality, and the ability of S. aureus to cause disease is absolutely dependent on the acquisition of iron from the host. The most abundant iron source to invading staphylococci is in the form of the porphyrin heme. S. aureus is capable of acquiring nutrient iron from heme and hemoproteins via two heme-acquisition systems, the iron-regulated surface determinant system (Isd) and the heme transport system (Hts). Heme acquisition through these systems is involved in staphylococcal pathogenesis suggesting that the intracellular fate of heme plays a significant role in the infectious process. The valuable heme molecule presents a paradox to invading bacteria because although heme is an abundant source of nutrient iron, the extreme reactivity of heme makes it toxic at high concentrations. Therefore, bacteria must regulate the levels of intracellular heme to avoid toxicity. Although the molecular mechanisms responsible for staphylococcal heme acquisition are beginning to emerge, the mechanisms by which S. aureus regulate intracellular heme homeostasis are largely unknown. In this review we describe three potential fates of host-derived heme acquired by S. aureus during infection: (i) degradation for use as a nutrient iron source, (ii) incorporation into bacterial heme-binding proteins for use as an enzyme cofactor, or (iii) efflux through a dedicated ABC-type transport system. We hypothesize that the ultimate fate of exogenously acquired heme in S. aureus is dependent upon the intracellular and extracellular availability of both iron and heme.

PLOS Pathogens, 2006

Staphylococcus aureus pathogenesis is significantly influenced by the iron status of the host. Ho... more Staphylococcus aureus pathogenesis is significantly influenced by the iron status of the host. However, the regulatory impact of host iron sources on S. aureus gene expression remains unknown. In this study, we combine multivariable difference gel electrophoresis and mass spectrometry with multivariate statistical analyses to systematically cluster cellular protein response across distinct iron-exposure conditions. Quadruplicate samples were simultaneously analyzed for alterations in protein abundance and/or post-translational modification state in response to environmental (iron chelation, hemin treatment) or genetic (Dfur) alterations in bacterial iron exposure. We identified 120 proteins representing several coordinated biochemical pathways that are affected by changes in iron-exposure status. Highlighted in these experiments is the identification of the heme-regulated transport system (HrtAB), a novel transport system which plays a critical role in staphylococcal heme metabolism. Further, we show that regulated overproduction of acidic end-products brought on by iron starvation decreases local pH resulting in the release of iron from the host iron-sequestering protein transferrin. These findings reveal novel strategies used by S. aureus to acquire scarce nutrients in the hostile host environment and begin to define the iron and heme-dependent regulons of S. aureus. Citation: Friedman DB, Stauff DL, Pishchany G, Whitwell CW, Torres VJ, et al. (2006) Staphylococcus aureus redirects central metabolism to increase iron availability. PLoS Pathog 2(8): e87.

Cell Host & Microbe, 2007

Staphylococcus aureus, a bacterium responsible for tremendous morbidity and mortality worldwide, ... more Staphylococcus aureus, a bacterium responsible for tremendous morbidity and mortality worldwide, exists as a harmless commensal organism in approximately 25% of the human population. Identifying the molecular machinery that is activated upon infection is central to understanding staphylococcal pathogenesis. We describe here the Heme-Sensor System (HssRS) that responds to heme exposure and activates expression of the Heme Regulated Transporter (HrtAB). The coordinated activities of HssRS and HrtAB maintain intracellular heme homeostasis and modulate S. aureus virulence. Inactivation of the Hss or Hrt systems leads to increased virulence in a vertebrate infection model, a phenotype that is associated with an inhibited innate immune response. Genomic analyses have identified orthologous Hss and Hrt systems in Bacillus anthracis, Listeria monocytogenes, and Enterococcus faecalis, suggesting a conserved regulatory system by which Gram positive pathogens sense heme as a molecular marker of internal host tissue and modulate virulence.

Science, 2008

Bacterial infection often results in the formation of tissue abscesses, which represent the prima... more Bacterial infection often results in the formation of tissue abscesses, which represent the primary site of interaction between invading bacteria and the innate immune system. We identify the host protein calprotectin as a neutrophil-dependent factor expressed inside Staphylococcus aureus abscesses. Neutrophil-derived calprotectin inhibited S. aureus growth through chelation of nutrient Mn2+ and Zn2+: an activity that results in reprogramming of the bacterial transcriptome. The abscesses of mice lacking calprotectin were enriched in metal, and staphylococcal proliferation was enhanced in these metal-rich abscesses. These results demonstrate that calprotectin is a critical factor in the innate immune response to infection and define metal chelation as a strategy for inhibiting microbial growth inside abscessed tissue.

Biometals, 2007

The bacterial pathogen Staphylococcus aureus is responsible for a significant amount of human mor... more The bacterial pathogen Staphylococcus aureus is responsible for a significant amount of human morbidity and mortality, and the ability of S. aureus to cause disease is absolutely dependent on the acquisition of iron from the host. The most abundant iron source to invading staphylococci is in the form of the porphyrin heme. S. aureus is capable of acquiring nutrient iron from heme and hemoproteins via two heme-acquisition systems, the iron-regulated surface determinant system (Isd) and the heme transport system (Hts). Heme acquisition through these systems is involved in staphylococcal pathogenesis suggesting that the intracellular fate of heme plays a significant role in the infectious process. The valuable heme molecule presents a paradox to invading bacteria because although heme is an abundant source of nutrient iron, the extreme reactivity of heme makes it toxic at high concentrations. Therefore, bacteria must regulate the levels of intracellular heme to avoid toxicity. Although the molecular mechanisms responsible for staphylococcal heme acquisition are beginning to emerge, the mechanisms by which S. aureus regulate intracellular heme homeostasis are largely unknown. In this review we describe three potential fates of host-derived heme acquired by S. aureus during infection: (i) degradation for use as a nutrient iron source, (ii) incorporation into bacterial heme-binding proteins for use as an enzyme cofactor, or (iii) efflux through a dedicated ABC-type transport system. We hypothesize that the ultimate fate of exogenously acquired heme in S. aureus is dependent upon the intracellular and extracellular availability of both iron and heme.

PLOS Pathogens, 2006

Staphylococcus aureus pathogenesis is significantly influenced by the iron status of the host. Ho... more Staphylococcus aureus pathogenesis is significantly influenced by the iron status of the host. However, the regulatory impact of host iron sources on S. aureus gene expression remains unknown. In this study, we combine multivariable difference gel electrophoresis and mass spectrometry with multivariate statistical analyses to systematically cluster cellular protein response across distinct iron-exposure conditions. Quadruplicate samples were simultaneously analyzed for alterations in protein abundance and/or post-translational modification state in response to environmental (iron chelation, hemin treatment) or genetic (Dfur) alterations in bacterial iron exposure. We identified 120 proteins representing several coordinated biochemical pathways that are affected by changes in iron-exposure status. Highlighted in these experiments is the identification of the heme-regulated transport system (HrtAB), a novel transport system which plays a critical role in staphylococcal heme metabolism. Further, we show that regulated overproduction of acidic end-products brought on by iron starvation decreases local pH resulting in the release of iron from the host iron-sequestering protein transferrin. These findings reveal novel strategies used by S. aureus to acquire scarce nutrients in the hostile host environment and begin to define the iron and heme-dependent regulons of S. aureus. Citation: Friedman DB, Stauff DL, Pishchany G, Whitwell CW, Torres VJ, et al. (2006) Staphylococcus aureus redirects central metabolism to increase iron availability. PLoS Pathog 2(8): e87.