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  • Nitrate assimilation  (2)
  • membrane-bound Fe(III) reductase  (2)
  • Dimethylsulphoxide  (1)
  • 1
    Electronic Resource
    Electronic Resource
    The influence of chelating agents upon the dissimilatory reduction of Fe(III) byShewanella putrefaciens. Part 2. Oxo-and hydroxo-bridged polynuclear Fe(III) complexes (1996)
    Springer
    BioMetals 9 (1996), S. 291-301 
    Details
    ISSN: 1572-8773
    Keywords: dissimilatory Fe(III) reduction ; membrane-bound Fe(III) reductase ; polynuclear Fe(III) complexes ; Shewanella putrefaciens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The susceptibility to dissimilatory reduction of polynuclear oxo- and hydroxo-bridged Fe(III) complexes byShewanella putrefaciens intact cells and membranes has been investigated. These complexes were ligated by the potential tetradentates heidi (H3heidi =N-(2-hydroxyethyl)iminodiacetic acid) or nta (H3nta = nitrilotriacetic acid), or the potential tridentate ida (H2ida = iminodiacetic acid). A number of defined small complexes with varied nuclearity and solubility properties were employed, as well as undefined species prepared by mixing different molar ratios of ida or heidi:Fe(III) in solution. The rates of Fe(III) reduction determined by an assay for Fe(II) formation with ferrozine were validated by monitoringc-type cytochrome oxidation and re-reduction associated with electron transport. For the undefined Fe(III) polymeric species, reduction rates in whole cells and membranes were considerably faster in the presence of heidi compared to ida. This is believed to result from generally smaller and more reactive clusters forming with heidi as a consequence of the alkoxo function of this ligand being able to bridge between Fe(III) nuclei, with access to an Fe(III) reductase located at the cytoplasmic membrane being of some importance. The increases in reduction rates of the undefined ida species with Fe(III) using membranes relative to whole cells reinforce such a view. Using soluble synthetic Fe(III) clusters, slow reduction was noted for an oxo-bridged dimer coordinatively saturated with ida and featuring unligated carboxylates. This suggests that sterically hindering the cation can influence enzyme action. A heidi dimer and a heidi multimer (17 or 19 Fe(III) nuclei), which are both of poor solubility, were found to be reduced by whole cells, but dissimilation rates increased markedly using membranes. These data suggest that Fe(III) reductase activity may be located at both the outer membrane and the cytoplasmic membrane ofS. putrefaciens. Slower reduction of the heidi multimer relative to the heidi dimer reflects the presence of a central hydroxo(oxo)-bridged core containing nine Fe(III) nuclei within the former cluster. This unit is a poor substrate for dissimilation, owing to the fact that the Fe(III) is not ligated by aminocarboxylate. The faster reduction noted for the heidi dimer in membranes than for a soluble ida monomer suggests that the presence of ligating water molecules may relieve steric hindrance to enzyme attack. Furthermore, reduction of an insoluble oxo-bridged nta dimer featuring ligating water molecules in intact cells was faster than that of a soluble monomer coordinatively saturated by nta and possessing an unligated carboxylate. This suggests that steric factors may override solubility considerations with respect to the susceptibility to reduction of certain Fe(III) complexes by the bacterium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00817930
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  • 2
    Electronic Resource
    Electronic Resource
    The influence of chelating agents upon the dissimilatory reduction of Fe(III) by Shewanella putrefaciens (1995)
    Springer
    BioMetals 8 (1995), S. 163-173 
    Details
    ISSN: 1572-8773
    Keywords: cytochrome oxidation ; dissimilatory Fe(III) reduction ; Fe(III) chelators ; membrane-bound Fe(III) reductase ; Shewanella putrefaciens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The ability of S. putrefaciens to reduce Fe(III) complexed by a variety of ligands has been investigated. All of the ligands tested caused the cation to be more susceptible to reduction by harvested whole cells than when uncomplexed, although some complexes were more readily reduced than others. Monitoring rates of reduction by a ferrozine assay for Fe(II) formation proved inadequate using Fe(III) ligands giving Fe(II) complexes of low kinetic lability (e.g. EDTA). A more suitable assay for Fe(III) reduction in the presence of such ligands proved to be the observation of associated cytochrome oxidation and re-reduction. Where possible, an assay for Fe(III) reduction based upon the disappearance of Fe(III) complex was also employed. Reduction of all Fe(III) complexes tested was totally inhibited by the presence of O2, partially inhibited by HQNO and slower in the absence of a physiological electron donor. Upon cell fractionation, Fe(III) reductase activity was detected exclusively in the membranes. Using different physiological electron donors in assays on membranes, relative reduction rates of Fe(III) complexes complemented the data from whole cells. The differences in susceptibility to reduction of the various complexes are discussed, as is evidence for the respiratory nature of the reduction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00142016
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  • 3
    Electronic Resource
    Electronic Resource
    The activities of two pathways of nitrate reduction in Rhodopseudomonas capsulata (1985)
    Springer
    Archives of microbiology 142 (1985), S. 403-408 
    Details
    ISSN: 1432-072X
    Keywords: Nitrate assimilation ; Nitrate dissimilation ; Ammonium regulation ; Rhodopseudomonas capsulata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract (1) The disappearance of nitrate from suspensions of intact, washed cells of Rhodopseudomonas capsulata strain N22DNAR+ was measured with an ion selective electrode. In samples taken from phototrophic cultures grown to late exponential phase, nitrate disappearance was partially inhibited by light but was not affected by the presence of ammonium. Nitrate disappearance from samples from low density cultures in the early exponential phase of growth was first inhibited and later stimulated by light. In these cells ammonium ions inhibited the light-dependent but not the dark disappearance of nitrate. It is concluded that cells in the early exponential phase of growth possess both an ammonium-sensitive, assimilatory pathway for nitrate reduction (NRI) and an ammonium-insensitive pathway for nitrate reduction (NRII) which is linked to respiratory electron flow and energy conservation. In cells harvested in late exponential phase only the respiratory pathway for pitrate reduction is detectable. (2) Nitrate reduction, as judged by the oxidation of reduced methyl viologen by anaerobic cell suspensions, was measured at high rates in those strains of R. capsulata (AD2, BK5, N22DNAR+) which are believed to possess NRII activity but not in those strains (Kbl, R3, N22) which only manifest the ammonium-sensitive NRI pathway. On this basis we have used nitrate-dependent oxidation of reduced methyl viologen as a diagnostic test for the nitrate reductase of NRII in cells harvested from cultures of R. capsulata strain AD2. The activity was readily detectable in cells from cultures grown aerobically in the dark with ammonium nitrate as source of nitrogen. When the oxygen supply to the culture was withdrawn, the level of methyl viologen-dependent nitrate reductase increased considerably and nitrite accumulated in the culture medium. Upon reconnecting the oxygen supply, methyl viologen-dependent nitrate reductase activity decreased and the reduction of nitrate to nitrite in the culture was inhibited. It is concluded that the respiratory nitrate reductase activity is regulated by the availability of electron transport pathways that are linked to the generation of a proton electrochemical gradient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00491912
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  • 4
    Electronic Resource
    Electronic Resource
    Electron flow to dimethylsulphoxide or trimethylamine-N-oxide generates a membrane potential in Rhodopseudomonas capsulata (1983)
    Springer
    Archives of microbiology 136 (1983), S. 300-305 
    Details
    ISSN: 1432-072X
    Keywords: Photosynthetic bacteria ; Electron transport ; Rhodopseudomonas capsulata ; Membrane potential ; Dimethylsulphoxide ; Trimethylamine-N-oxide ; Fermentation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Under dark and essentially anaerobic conditions electron flow to either dimethylsulphoxide or trimethylamine-N-oxide in cells of Rhodopseudomonas capsulata has been shown to generate a membrane potential. This conclusion is based on the observation of a red shift in the carotenoid absorption band which is a well characterised indicator of membrane potential in this bacterium. The magnitude of the dimethylsulphoxide- or trimethylamine-N-oxide-dependent membrane potential was reduced either by a protonophore uncoupler of oxidative phosphorylation or synergistically by a combination of a protonophore plus rotenone, an inhibitor of electron flow from NADH dehydrogenase. These findings, together with the observation that venturicidin, an inhibitor of the proton translocating ATPase, did not reduce the membrane potential, show that electron flow to dimethylsulphoxide or trimethylamine-N-oxide is coupled to proton translocation. Thus contrary to some previous proposals dark and anaerobic growth of Rps. capsulata in the presence of dimethylsulphoxide or trimethylamine-N-oxide cannot be regarded as purely fermentative.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00425221
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  • 5
    Electronic Resource
    Electronic Resource
    Rationalization of properties of nitrate reductases in Rhodopseudomonas capsulata (1984)
    Springer
    Archives of microbiology 137 (1984), S. 344-349 
    Details
    ISSN: 1432-072X
    Keywords: Nitrate reductase ; Photosynthetic bacteria ; Anaerobic respiration ; Nitrate assimilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 1. The properties of nitrate reductase activities have been compared in several strains of Rhodopseudomonas capsulata grown phototrophically in the presence of nitrate as sole nitrogen source. 2. Strains AD2 and BK5 resemble the spontaneous mutant N22DNAR+ (described by McEwan et al. 1982 FEBS Lett. 150, 277\2-280) in that reduction of nitrate was inhibited by either illumination or oxygen but not by NH 4 + , and that electron flow to nitrate under dark anaerobic conditions generated a cytoplasmic membrane potential (as judged by an electrochromic shift in the absorbance spectrum of endogenous carotenoid pigments). In contrast disappearance of nitrate from suspensions of strains N22 and St. Louis was dependent upon illumination and was inhibited by NH 4 + . Membrane potentials were not generated by addition of nitrate in the dark to N22, St. Louis or strain Kbl. 3. Nitrate reductase was shown to be located in the periplasmic space of both strain AD2 and mutant N22DNAR+. The nitrate reductase activity in cells of AD2 and N22DNAR+ was relatively insensitive to azide, with 0.5mM azide required for 50% inhibition. The nitrate reductase of strain BK5 was more strongly associated with the cytoplasmic membrane and no conclusion could be reached about whether it was located on the periplasmic or cytoplasmic surface. In BK5 cells nitrate reductase activity was sensitive to low concentrations of azide (50% inhibition with 2 \gmM azide). It is proposed that functionally the nitrate reductase activity in strains AD2, BK5 and N22DNAR+ has identical roles. These roles are suggested to include: (i) The first step in the assimilation of nitrate. (ii). Provision of an alternative electron acceptor to oxygen for generating a membrane potential. (iii). A mechanism for disposing of excess reducing equivalents in the maintenance of balanced growth. This type of nitrate reductase, especially in AD2 and N22DNAR+, appears to resemble that described in a denitrifying strain of Rps. sphaeroides, but to differ markedly from its membrane-bound counterpart in other bacteria including the denitrifying Paracoccus denitrificans and Escherichia coli. 4. In other strains of Rps. capsulata including St. Louis, N22 and Kbl, only an assimilatory nitrate reductase, whose activity in intact cells is relatively sensitive to azide, is present in anaerobic, phototrophic cultures grown with nitrate as nitrogen source. As this reductase cannot be detected after breakage of cells, no conclusion can be made as to its location in the cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00410732
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