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Davide Zannoni - One of the best experts on this subject based on the ideXlab platform.
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Structural and electrochemical characterization of lawsone-dependent production of tellurium-metal nanoprecipitates by photosynthetic cells of Rhodobacter capsulatus.
Bioelectrochemistry (Amsterdam Netherlands), 2020Co-Authors: Roberto Borghese, Francesca Borsetti, Marco Malferrari, Marco Brucale, Luca Ortolani, Martina Franchini, Stefania Rapino, Davide ZannoniAbstract:Cells of the facultative photosynthetic bacterium Rhodobacter capsulatus exploit the simultaneous presence in the cultural medium of the toxic oxyanion Tellurite (TeO32-) and the redox mediator lawsone (2-hydroxy-1,4-naphthoquinone) by reducing Tellurite to metal Te0 nanoprecipitates (TeNPs) outside the cells. Here we have studied the mechanism by which lawsone interacts with metabolically active cells and analysed both structure and composition of the TeNPs collected from the growth medium of phototrophycally grown R. capsulatus. High Resolution Transmission Electron Microscopy (HR-TEM) images and Energy-Dispersive X-ray (EDX) microanalysis of TeNPs showed a central core of polycrystalline tellurium interspersed in an organic matrix with a predominant protein-based composition. The main proteins from Te0 nanostructures were identified by Liquid Chromatography tandem-Mass Spectrometry and were all correlated with the cell outer membrane composition. The interaction of reduced lawsone with Tellurite and with the bacterial cells was probed by Cyclic Voltammetry and Scanning ElectroChemical Microscopy (SECM). We concluded that lawsone is required for the reduction of Tellurite to metal Te0 in a reaction mechanism dependent on reducing equivalents deriving from the cell photosynthetic metabolism. SECM experiments demonstrate that lawsone, by diffusing inside the bacterial cells, is effectively available at the membrane site of the photosynthetic electron transport chain.
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Acetate permease (ActP) Is responsible for Tellurite (TeO32-) uptake and resistance in cells of the facultative phototroph Rhodobacter capsulatus.
Applied and Environmental Microbiology, 2009Co-Authors: Roberto Borghese, Davide ZannoniAbstract:The highly toxic oxyanion Tellurite has to enter the cytoplasm of microbial cells in order to fully express its toxicity. Here we show that in the phototroph Rhodobacter capsulatus, Tellurite exploits acetate permease (ActP) to get into the cytoplasm and that the levels of resistance and uptake are linked.
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the highly toxic oxyanion Tellurite teo 3 2 enters the phototrophic bacterium rhodobacter capsulatus via an as yet uncharacterized monocarboxylate transport system
Archives of Microbiology, 2008Co-Authors: Roberto Borghese, Daniele Marchetti, Davide ZannoniAbstract:The facultative phototroph Rhodobacter capsulatus takes up the highly toxic oxyanion Tellurite when grown under both photosynthetic and respiratory growth conditions. Previous works on Escherichia coli and R. capsulatus suggested that Tellurite uptake occurred through a phosphate transporter. Here we present evidences indicating that Tellurite enters R. capsulatus cells via a monocarboxylate transport system. Indeed, intracellular accumulation of Tellurite was inhibited by the addition of monocarboxylates such as pyruvate, lactate and acetate, but not by dicarboxylates like malate or succinate. Acetate was the strongest Tellurite uptake antagonist and this effect was concentration dependent, being already evident at 1 μM acetate. Conversely, Tellurite at 100 μM was able to restrict the acetate entry into the cells. Both Tellurite and acetate uptakes were energy dependent processes, since they were abolished by the protonophore FCCP and by the respiratory electron transport inhibitor KCN. Interestingly, cells grown on acetate, lactate or pyruvate showed a high level resistance to Tellurite, whereas cells grown on malate or succinate proved to be very sensitive to the oxyanion. Taking these data together, we propose that: (a) Tellurite enters R. capsulatus cells via an as yet uncharacterized monocarboxylate(s) transporter, (b) competition between acetate and Tellurite results in a much higher level of tolerance against the oxyanion and (c) the toxic action of Tellurite at the cytosolic level is significantly restricted by preventing Tellurite uptake.
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the thiol disulfide oxidoreductase dsbb mediates the oxidizing effects of the toxic metalloid Tellurite teo32 on the plasma membrane redox system of the facultative phototroph rhodobacter capsulatus
Journal of Bacteriology, 2007Co-Authors: Francesca Borsetti, Raymond J Turner, Francesco Francia, Davide ZannoniAbstract:The highly toxic oxyanion Tellurite (TeO32−) is a well known pro-oxidant in mammalian and bacterial cells. This work examines the effects of Tellurite on the redox state of the electron transport chain of the facultative phototroph Rhodobacter capsulatus, in relation to the role of the thiol:disulfide oxidoreductase DsbB. Under steady-state respiration, the addition of Tellurite (2.5 mM) to membrane fragments generated an extrareduction of the cytochrome pool (c- and b-type hemes); further, in plasma membranes exposed to Tellurite (0.25 to 2.5 mM) and subjected to a series of flashes of light, the rate of the QH2:cytochrome c (Cyt c) oxidoreductase activity was enhanced. The effect of Tellurite was blocked by the antibiotics antimycin A and/or myxothiazol, specific inhibitors of the QH2:Cyt c oxidoreductase, and, most interestingly, the membrane-associated thiol:disulfide oxidoreductase DsbB was required to mediate the redox unbalance produced by the oxyanion. Indeed, this phenomenon was absent from R. capsulatus MD22, a DsbB-deficient mutant, whereas the Tellurite effect was present in membranes from MD22/pDsbBWT, in which the mutant gene was complemented to regain the wild-type DsbB phenotype. These findings were taken as evidence that the membrane-bound thiol:disulfide oxidoreductase DsbB acts as an “electron conduit” between the hydrophilic metalloid and the lipid-embedded Q pool, so that in habitats contaminated with subinhibitory amounts of TeIV, the metalloid is likely to function as a disposal for the excess reducing power at the Q-pool level of facultative phototrophic bacteria.
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Tellurite effects on rhodobacter capsulatus cell viability and superoxide dismutase activity under oxidative stress conditions
Research in Microbiology, 2005Co-Authors: Francesca Borsetti, Roberto Borghese, Valentina Tremaroli, Francesca Michelacci, Christine Winterstein, Fevzi Daldal, Davide ZannoniAbstract:Abstract Cells of the facultative photosynthetic bacterium Rhodobacter capsulatus (MT1131 strain) incubated with 10 μg ml −1 of the toxic oxyanion Tellurite (TeO 2− 3 ) exhibited an increase in superoxide dismutase activity. The latter effect was also seen upon incubation with sublethal amounts of paraquat, a cytosolic generator of superoxide anions ( O 2 ⋅ − ), in parallel with a strong increase in Tellurite resistance (Te R ). A mutant strain (CW10) deficient in SenC, a protein with similarities to peroxiredoxin/thiol:disulfide oxidoreductases and a homologue of mitochondrial Sco proteins, was constructed by interposon mutagenesis via the gene transfer agent system. Notably, the absence of SenC affected R. capsulatus resistance to periplasmic O 2 ⋅ − generated by xanthine/xanthine oxidase but not to cytosolic O 2 ⋅ − produced by paraquat. Further, the absence of SenC did not affect R. capsulatus Tellurite resistance. We conclude that: (1) cytosolic-generated O 2 ⋅ − enhances Te R of this bacterial species; (2) small amounts of Tellurite increase SOD activity so as to mimic the early cell response to oxidative stress; (3) SenC protein is required in protection of R. capsulatus against periplasmic oxidative stress; and finally, (4) SenC protein is not involved in Te R , possibly because Tellurite does not generate O ⋅ − 2 at the periplasmic space level.
Francesca Borsetti - One of the best experts on this subject based on the ideXlab platform.
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Structural and electrochemical characterization of lawsone-dependent production of tellurium-metal nanoprecipitates by photosynthetic cells of Rhodobacter capsulatus.
Bioelectrochemistry (Amsterdam Netherlands), 2020Co-Authors: Roberto Borghese, Francesca Borsetti, Marco Malferrari, Marco Brucale, Luca Ortolani, Martina Franchini, Stefania Rapino, Davide ZannoniAbstract:Cells of the facultative photosynthetic bacterium Rhodobacter capsulatus exploit the simultaneous presence in the cultural medium of the toxic oxyanion Tellurite (TeO32-) and the redox mediator lawsone (2-hydroxy-1,4-naphthoquinone) by reducing Tellurite to metal Te0 nanoprecipitates (TeNPs) outside the cells. Here we have studied the mechanism by which lawsone interacts with metabolically active cells and analysed both structure and composition of the TeNPs collected from the growth medium of phototrophycally grown R. capsulatus. High Resolution Transmission Electron Microscopy (HR-TEM) images and Energy-Dispersive X-ray (EDX) microanalysis of TeNPs showed a central core of polycrystalline tellurium interspersed in an organic matrix with a predominant protein-based composition. The main proteins from Te0 nanostructures were identified by Liquid Chromatography tandem-Mass Spectrometry and were all correlated with the cell outer membrane composition. The interaction of reduced lawsone with Tellurite and with the bacterial cells was probed by Cyclic Voltammetry and Scanning ElectroChemical Microscopy (SECM). We concluded that lawsone is required for the reduction of Tellurite to metal Te0 in a reaction mechanism dependent on reducing equivalents deriving from the cell photosynthetic metabolism. SECM experiments demonstrate that lawsone, by diffusing inside the bacterial cells, is effectively available at the membrane site of the photosynthetic electron transport chain.
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the thiol disulfide oxidoreductase dsbb mediates the oxidizing effects of the toxic metalloid Tellurite teo32 on the plasma membrane redox system of the facultative phototroph rhodobacter capsulatus
Journal of Bacteriology, 2007Co-Authors: Francesca Borsetti, Raymond J Turner, Francesco Francia, Davide ZannoniAbstract:The highly toxic oxyanion Tellurite (TeO32−) is a well known pro-oxidant in mammalian and bacterial cells. This work examines the effects of Tellurite on the redox state of the electron transport chain of the facultative phototroph Rhodobacter capsulatus, in relation to the role of the thiol:disulfide oxidoreductase DsbB. Under steady-state respiration, the addition of Tellurite (2.5 mM) to membrane fragments generated an extrareduction of the cytochrome pool (c- and b-type hemes); further, in plasma membranes exposed to Tellurite (0.25 to 2.5 mM) and subjected to a series of flashes of light, the rate of the QH2:cytochrome c (Cyt c) oxidoreductase activity was enhanced. The effect of Tellurite was blocked by the antibiotics antimycin A and/or myxothiazol, specific inhibitors of the QH2:Cyt c oxidoreductase, and, most interestingly, the membrane-associated thiol:disulfide oxidoreductase DsbB was required to mediate the redox unbalance produced by the oxyanion. Indeed, this phenomenon was absent from R. capsulatus MD22, a DsbB-deficient mutant, whereas the Tellurite effect was present in membranes from MD22/pDsbBWT, in which the mutant gene was complemented to regain the wild-type DsbB phenotype. These findings were taken as evidence that the membrane-bound thiol:disulfide oxidoreductase DsbB acts as an “electron conduit” between the hydrophilic metalloid and the lipid-embedded Q pool, so that in habitats contaminated with subinhibitory amounts of TeIV, the metalloid is likely to function as a disposal for the excess reducing power at the Q-pool level of facultative phototrophic bacteria.
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Tellurite effects on rhodobacter capsulatus cell viability and superoxide dismutase activity under oxidative stress conditions
Research in Microbiology, 2005Co-Authors: Francesca Borsetti, Roberto Borghese, Valentina Tremaroli, Francesca Michelacci, Christine Winterstein, Fevzi Daldal, Davide ZannoniAbstract:Abstract Cells of the facultative photosynthetic bacterium Rhodobacter capsulatus (MT1131 strain) incubated with 10 μg ml −1 of the toxic oxyanion Tellurite (TeO 2− 3 ) exhibited an increase in superoxide dismutase activity. The latter effect was also seen upon incubation with sublethal amounts of paraquat, a cytosolic generator of superoxide anions ( O 2 ⋅ − ), in parallel with a strong increase in Tellurite resistance (Te R ). A mutant strain (CW10) deficient in SenC, a protein with similarities to peroxiredoxin/thiol:disulfide oxidoreductases and a homologue of mitochondrial Sco proteins, was constructed by interposon mutagenesis via the gene transfer agent system. Notably, the absence of SenC affected R. capsulatus resistance to periplasmic O 2 ⋅ − generated by xanthine/xanthine oxidase but not to cytosolic O 2 ⋅ − produced by paraquat. Further, the absence of SenC did not affect R. capsulatus Tellurite resistance. We conclude that: (1) cytosolic-generated O 2 ⋅ − enhances Te R of this bacterial species; (2) small amounts of Tellurite increase SOD activity so as to mimic the early cell response to oxidative stress; (3) SenC protein is required in protection of R. capsulatus against periplasmic oxidative stress; and finally, (4) SenC protein is not involved in Te R , possibly because Tellurite does not generate O ⋅ − 2 at the periplasmic space level.
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effects of the metalloid oxyanion Tellurite teo32 on growth characteristics of the phototrophic bacterium rhodobacter capsulatus
Applied and Environmental Microbiology, 2004Co-Authors: Roberto Borghese, Francesca Borsetti, Paola Foladori, G. Ziglio, Davide ZannoniAbstract:This work examines the effects of potassium Tellurite (K2TeO3) on the cell viability of the facultative phototroph Rhodobacter capsulatus. There was a growth mode-dependent response in which cultures anaerobically grown in the light tolerate the presence of up to 250 to 300 μg of Tellurite (TeO32−) per ml, while dark-grown aerobic cells were inhibited at Tellurite levels as low as 2 μg/ml. The Tellurite sensitivity of aerobic cultures was evident only for growth on minimal salt medium, whereas it was not seen during growth on complex medium. Notably, through the use of flow cytometry, we show that the cell membrane integrity was strongly affected by Tellurite during the early growth phase (≤50% viable cells); however, at the end of the growth period and in parallel with massive Tellurite intracellular accumulation as elemental Te0 crystallites, recovery of cytoplasmic membrane integrity was apparent (≥90% viable cells), which was supported by the development of a significant membrane potential (Δψ = 120 mV). These data are taken as evidence that in anaerobic aquatic habitats, the facultative phototroph R. capsulatus might act as a natural scavenger of the highly soluble and toxic oxyanion Tellurite.
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Tellurite uptake by cells of the facultative phototroph rhodobacter capsulatus is a δph dependent process
FEBS Letters, 2003Co-Authors: Francesca Borsetti, Antonio Toninello, Davide ZannoniAbstract:Abstract The uptake by light-grown cells of Rhodobacter capsulatus of the highly toxic metalloid oxyanion Tellurite (TeO 3 2− ) was examined. We show that Tellurite is rapidly taken up by illuminated cells in a process which is inhibited by the protonophore carbonyl cyanide- p -trifluoromethoxyphenyl-hydrazone (FCCP) and by the K + /H + exchanger nigericin. Notably, the light-driven membrane potential (Δ ψ ) is enhanced by K 2 TeO 3 ≥200 μM. Further, Tellurite uptake is largely insensitive to valinomycin, strongly repressed by the sulfhydryl reagent N -ethylethylmaleimide (NEM) and competitively inhibited by phosphate. We conclude that Tellurite is transported into cells by a ΔpH-dependent, non-electrogenic process which is likely to involve the phosphate transporter (PiT family).
Roberto Borghese - One of the best experts on this subject based on the ideXlab platform.
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Structural and electrochemical characterization of lawsone-dependent production of tellurium-metal nanoprecipitates by photosynthetic cells of Rhodobacter capsulatus.
Bioelectrochemistry (Amsterdam Netherlands), 2020Co-Authors: Roberto Borghese, Francesca Borsetti, Marco Malferrari, Marco Brucale, Luca Ortolani, Martina Franchini, Stefania Rapino, Davide ZannoniAbstract:Cells of the facultative photosynthetic bacterium Rhodobacter capsulatus exploit the simultaneous presence in the cultural medium of the toxic oxyanion Tellurite (TeO32-) and the redox mediator lawsone (2-hydroxy-1,4-naphthoquinone) by reducing Tellurite to metal Te0 nanoprecipitates (TeNPs) outside the cells. Here we have studied the mechanism by which lawsone interacts with metabolically active cells and analysed both structure and composition of the TeNPs collected from the growth medium of phototrophycally grown R. capsulatus. High Resolution Transmission Electron Microscopy (HR-TEM) images and Energy-Dispersive X-ray (EDX) microanalysis of TeNPs showed a central core of polycrystalline tellurium interspersed in an organic matrix with a predominant protein-based composition. The main proteins from Te0 nanostructures were identified by Liquid Chromatography tandem-Mass Spectrometry and were all correlated with the cell outer membrane composition. The interaction of reduced lawsone with Tellurite and with the bacterial cells was probed by Cyclic Voltammetry and Scanning ElectroChemical Microscopy (SECM). We concluded that lawsone is required for the reduction of Tellurite to metal Te0 in a reaction mechanism dependent on reducing equivalents deriving from the cell photosynthetic metabolism. SECM experiments demonstrate that lawsone, by diffusing inside the bacterial cells, is effectively available at the membrane site of the photosynthetic electron transport chain.
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Acetate permease (ActP) Is responsible for Tellurite (TeO32-) uptake and resistance in cells of the facultative phototroph Rhodobacter capsulatus.
Applied and Environmental Microbiology, 2009Co-Authors: Roberto Borghese, Davide ZannoniAbstract:The highly toxic oxyanion Tellurite has to enter the cytoplasm of microbial cells in order to fully express its toxicity. Here we show that in the phototroph Rhodobacter capsulatus, Tellurite exploits acetate permease (ActP) to get into the cytoplasm and that the levels of resistance and uptake are linked.
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the highly toxic oxyanion Tellurite teo 3 2 enters the phototrophic bacterium rhodobacter capsulatus via an as yet uncharacterized monocarboxylate transport system
Archives of Microbiology, 2008Co-Authors: Roberto Borghese, Daniele Marchetti, Davide ZannoniAbstract:The facultative phototroph Rhodobacter capsulatus takes up the highly toxic oxyanion Tellurite when grown under both photosynthetic and respiratory growth conditions. Previous works on Escherichia coli and R. capsulatus suggested that Tellurite uptake occurred through a phosphate transporter. Here we present evidences indicating that Tellurite enters R. capsulatus cells via a monocarboxylate transport system. Indeed, intracellular accumulation of Tellurite was inhibited by the addition of monocarboxylates such as pyruvate, lactate and acetate, but not by dicarboxylates like malate or succinate. Acetate was the strongest Tellurite uptake antagonist and this effect was concentration dependent, being already evident at 1 μM acetate. Conversely, Tellurite at 100 μM was able to restrict the acetate entry into the cells. Both Tellurite and acetate uptakes were energy dependent processes, since they were abolished by the protonophore FCCP and by the respiratory electron transport inhibitor KCN. Interestingly, cells grown on acetate, lactate or pyruvate showed a high level resistance to Tellurite, whereas cells grown on malate or succinate proved to be very sensitive to the oxyanion. Taking these data together, we propose that: (a) Tellurite enters R. capsulatus cells via an as yet uncharacterized monocarboxylate(s) transporter, (b) competition between acetate and Tellurite results in a much higher level of tolerance against the oxyanion and (c) the toxic action of Tellurite at the cytosolic level is significantly restricted by preventing Tellurite uptake.
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Tellurite effects on rhodobacter capsulatus cell viability and superoxide dismutase activity under oxidative stress conditions
Research in Microbiology, 2005Co-Authors: Francesca Borsetti, Roberto Borghese, Valentina Tremaroli, Francesca Michelacci, Christine Winterstein, Fevzi Daldal, Davide ZannoniAbstract:Abstract Cells of the facultative photosynthetic bacterium Rhodobacter capsulatus (MT1131 strain) incubated with 10 μg ml −1 of the toxic oxyanion Tellurite (TeO 2− 3 ) exhibited an increase in superoxide dismutase activity. The latter effect was also seen upon incubation with sublethal amounts of paraquat, a cytosolic generator of superoxide anions ( O 2 ⋅ − ), in parallel with a strong increase in Tellurite resistance (Te R ). A mutant strain (CW10) deficient in SenC, a protein with similarities to peroxiredoxin/thiol:disulfide oxidoreductases and a homologue of mitochondrial Sco proteins, was constructed by interposon mutagenesis via the gene transfer agent system. Notably, the absence of SenC affected R. capsulatus resistance to periplasmic O 2 ⋅ − generated by xanthine/xanthine oxidase but not to cytosolic O 2 ⋅ − produced by paraquat. Further, the absence of SenC did not affect R. capsulatus Tellurite resistance. We conclude that: (1) cytosolic-generated O 2 ⋅ − enhances Te R of this bacterial species; (2) small amounts of Tellurite increase SOD activity so as to mimic the early cell response to oxidative stress; (3) SenC protein is required in protection of R. capsulatus against periplasmic oxidative stress; and finally, (4) SenC protein is not involved in Te R , possibly because Tellurite does not generate O ⋅ − 2 at the periplasmic space level.
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effects of the metalloid oxyanion Tellurite teo32 on growth characteristics of the phototrophic bacterium rhodobacter capsulatus
Applied and Environmental Microbiology, 2004Co-Authors: Roberto Borghese, Francesca Borsetti, Paola Foladori, G. Ziglio, Davide ZannoniAbstract:This work examines the effects of potassium Tellurite (K2TeO3) on the cell viability of the facultative phototroph Rhodobacter capsulatus. There was a growth mode-dependent response in which cultures anaerobically grown in the light tolerate the presence of up to 250 to 300 μg of Tellurite (TeO32−) per ml, while dark-grown aerobic cells were inhibited at Tellurite levels as low as 2 μg/ml. The Tellurite sensitivity of aerobic cultures was evident only for growth on minimal salt medium, whereas it was not seen during growth on complex medium. Notably, through the use of flow cytometry, we show that the cell membrane integrity was strongly affected by Tellurite during the early growth phase (≤50% viable cells); however, at the end of the growth period and in parallel with massive Tellurite intracellular accumulation as elemental Te0 crystallites, recovery of cytoplasmic membrane integrity was apparent (≥90% viable cells), which was supported by the development of a significant membrane potential (Δψ = 120 mV). These data are taken as evidence that in anaerobic aquatic habitats, the facultative phototroph R. capsulatus might act as a natural scavenger of the highly soluble and toxic oxyanion Tellurite.
Pengfei Wang - One of the best experts on this subject based on the ideXlab platform.
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Tellurite Glass and Its Application in Lasers
Advanced Functional Materials, 2020Co-Authors: Pengfei Wang, Shunbin Wang, Shijie Jia, Yuxuan Jiang, Xin Wang, Elfed LewisAbstract:This chapter provides expert coverage of the physical properties of new noncrystalline solids—Tellurite glass and the latest laser applications of the material—offering insights into innovative applications for laser and sensing devices, among others. In particular, there is a focus on specialty optical fibers, supercontinuum generation and laser devices, and luminescence properties for laser applications. This chapter also addresses the fabrication and optical properties and uses of Tellurite glasses in optical fibers and optical microcavities, the significance of from near infrared (NIR) to mid-infrared (MIR) emissions and the development of Tellurite glass-based microcavity lasers. The important attributes of these Tellurite glasses and their applications in lasers were discussed in this chapter.
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tm3 ho3 codoped Tellurite glass microsphere laser in the 147 μm wavelength region
Optics Letters, 2019Co-Authors: Angzhen Li, Yindong Zhang, Anping Yang, Shunbin Wang, Wenhao Li, Zhiyong Yang, Elfed Lewis, Meng Zhang, Gilberto Brambilla, Pengfei WangAbstract:: In this Letter, a Tm3+-Ho3+ codoped Tellurite glass microsphere laser in the 1.47 μm wavelength region is described. Using a traditional tapered microfiber-microsphere coupling method, multimode and single-mode lasing around the wavelength of 1.47 μm is observed using an 802 nm laser diode as a pump source. This Tm3+-Ho3+ codoped Tellurite glass microsphere laser can be used in near-infrared telecommunications, biomedical, and astrophysical applications.
Raymond J Turner - One of the best experts on this subject based on the ideXlab platform.
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the thiol disulfide oxidoreductase dsbb mediates the oxidizing effects of the toxic metalloid Tellurite teo32 on the plasma membrane redox system of the facultative phototroph rhodobacter capsulatus
Journal of Bacteriology, 2007Co-Authors: Francesca Borsetti, Raymond J Turner, Francesco Francia, Davide ZannoniAbstract:The highly toxic oxyanion Tellurite (TeO32−) is a well known pro-oxidant in mammalian and bacterial cells. This work examines the effects of Tellurite on the redox state of the electron transport chain of the facultative phototroph Rhodobacter capsulatus, in relation to the role of the thiol:disulfide oxidoreductase DsbB. Under steady-state respiration, the addition of Tellurite (2.5 mM) to membrane fragments generated an extrareduction of the cytochrome pool (c- and b-type hemes); further, in plasma membranes exposed to Tellurite (0.25 to 2.5 mM) and subjected to a series of flashes of light, the rate of the QH2:cytochrome c (Cyt c) oxidoreductase activity was enhanced. The effect of Tellurite was blocked by the antibiotics antimycin A and/or myxothiazol, specific inhibitors of the QH2:Cyt c oxidoreductase, and, most interestingly, the membrane-associated thiol:disulfide oxidoreductase DsbB was required to mediate the redox unbalance produced by the oxyanion. Indeed, this phenomenon was absent from R. capsulatus MD22, a DsbB-deficient mutant, whereas the Tellurite effect was present in membranes from MD22/pDsbBWT, in which the mutant gene was complemented to regain the wild-type DsbB phenotype. These findings were taken as evidence that the membrane-bound thiol:disulfide oxidoreductase DsbB acts as an “electron conduit” between the hydrophilic metalloid and the lipid-embedded Q pool, so that in habitats contaminated with subinhibitory amounts of TeIV, the metalloid is likely to function as a disposal for the excess reducing power at the Q-pool level of facultative phototrophic bacteria.
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Differences in biofilm and planktonic cell mediated reduction of metalloid oxyanions.
Fems Microbiology Letters, 2004Co-Authors: Joe J Harrison, Howard Ceri, Carol A. Stremick, Raymond J TurnerAbstract:This study compares Staphylococcus aureus ATCC 29213 and Pseudomonas aeruginosa ATCC 27853 biofilm and planktonic cell susceptibility to the selenium and tellurium oxyanions selenite (SeO32−), tellurate (TeO42−), and Tellurite (TeO32−). P. aeruginosa planktonic and biofilm cultures reduced the selenium and tellurium oxyanions to orange and black end-products (respectively) and were equally tolerant to killing by these metalloid compounds. S. aureus planktonic cell cultures processed these metalloid oxyanions in a similar way, but the corresponding biofilm cultures did not. S. aureus biofilms were approximately two and five times more susceptible to killing by tellurate and Tellurite (respectively) than the corresponding planktonic cultures. Our data indicate that the means of reducing metalloid oxyanions may differ between the physiology displayed in biofilm and planktonic cultures of the same bacterial strain.
