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Evidence of a chemiosmotic model for halorespiration in desulfomonile tiedjei DCB-1 Louie, Tai Man
Abstract
Desulfomonile tiedjeiDCB-1, a sulfate-reducing bacterium, conserves energy for growth from reductive dehalogenation of 3-chlorobenzoate by an uncharacterized anaerobic respiratory process. Different electron carriers and respiratory enzymes of D. tiedjei cells grown under conditions for reductive dehalogenation, pyruvate fermentation and sulfate respiration were therefore examined quantitatively. Only cytochromes c were detected in the soluble and membrane fractions of cells grown under the three conditions. These cytochromes include a constitutively expressed 17-kDa cytochrome c, which was detected in cells grown under all three conditions, and a unique diheme cytochrome c with an apparent molecular mass of 50 kDa, which was present only in the membrane fractions of dehalogenatingcells. This inducible cytochrome c had a very negative midpoint potential of --342 mV. Absorption spectra and the putative gene sequence suggest that the inducible cytochrome c is substantially different from previously characterized cytochromes. Reductive dehalogenation activity of D. tiedjei-was shown to be dependent on 1,4-naphthoquinone, a possible precursor for a respiratory quinone. Moreover, cell suspension experiments indicated that reductive dehalogenation of D. tiedjei was inhibited by the respiratory quinone inhibitor, 2-heptyl-4-hydroxyquinoline JV-oxide, suggesting a respiratory quinone is involved in the electron transport chain coupled to reductive dehalogenation. However, no ubiquinone or menaquinone could be extracted from D. tiedjei. Rather, an UV-absorbing, quinone-like molecule or quinoid, was extracted. The oxidized and reduced UV-absorption spectra of the quinoid were similar in some ways to those of ubiquinones and pyrrolo-quinoline quinones, respectively. But the quinoid was different from these common respiratory quinones in chemical structure according to mass spectrometric analysis. ATP sulfurylase, APS reductase and desulfoviridin, the enzymes involved in sulfate-reduction, appeared to be constitutively expressed in the cytoplasm of D. tiedjei cells grown under the three metabolic conditions. An inducible, periplasmic hydrogenase was detected in cells grown under reductive-dehalogenating and pyruvate-fermenting conditions. An inducible, membrane-bound, periplasm-oriented formate dehydrogenase was active only in cells grown with formate as electron donor; while, a cytoplasmic formate dehydrogenase was detected in cells grown under reductive-dehalogenating and pyruvate-fermenting conditions. Results from dehalogenation assays with D. tiedjei cell suspensions suggest the membrane-bound reductive dehalogenaseis facing the cytoplasm . The inducible cytochrome c, or the quinoid, alone or in combination, failed to replace reduced methyl viologen as the electron donor for the reductive dehalogenase in vitro. The putative gene sequence of the reductive dehalogenase small subunit was determined from inverse PCR products amplified from genomic DNA, but the sequence did not have substantial similarity to any sequences in GenBank. These data clearly demonstrate that D. tiedjei possesses elements necessary for producing protons directly in the periplasm, generating a proton-motive force across the cytoplasmic membrane. However, the data did not exclude the existence of additional transmembrane proton translocation mechanisms, which would further enhance the proton-motive force.
Item Metadata
Title |
Evidence of a chemiosmotic model for halorespiration in desulfomonile tiedjei DCB-1
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1998
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Description |
Desulfomonile tiedjeiDCB-1, a sulfate-reducing bacterium, conserves energy for growth
from reductive dehalogenation of 3-chlorobenzoate by an uncharacterized anaerobic respiratory
process. Different electron carriers and respiratory enzymes of D. tiedjei cells grown under
conditions for reductive dehalogenation, pyruvate fermentation and sulfate respiration were
therefore examined quantitatively. Only cytochromes c were detected in the soluble and
membrane fractions of cells grown under the three conditions. These cytochromes include a
constitutively expressed 17-kDa cytochrome c, which was detected in cells grown under all three
conditions, and a unique diheme cytochrome c with an apparent molecular mass of 50 kDa, which
was present only in the membrane fractions of dehalogenatingcells. This inducible cytochrome c
had a very negative midpoint potential of --342 mV. Absorption spectra and the putative gene
sequence suggest that the inducible cytochrome c is substantially different from previously
characterized cytochromes. Reductive dehalogenation activity of D. tiedjei-was shown to be
dependent on 1,4-naphthoquinone, a possible precursor for a respiratory quinone. Moreover, cell
suspension experiments indicated that reductive dehalogenation of D. tiedjei was inhibited by the
respiratory quinone inhibitor, 2-heptyl-4-hydroxyquinoline JV-oxide, suggesting a respiratory
quinone is involved in the electron transport chain coupled to reductive dehalogenation. However,
no ubiquinone or menaquinone could be extracted from D. tiedjei. Rather, an UV-absorbing,
quinone-like molecule or quinoid, was extracted. The oxidized and reduced UV-absorption
spectra of the quinoid were similar in some ways to those of ubiquinones and pyrrolo-quinoline
quinones, respectively. But the quinoid was different from these common respiratory quinones in
chemical structure according to mass spectrometric analysis. ATP sulfurylase, APS reductase and
desulfoviridin, the enzymes involved in sulfate-reduction, appeared to be constitutively
expressed in the cytoplasm of D. tiedjei cells grown under the three metabolic conditions. An inducible, periplasmic hydrogenase was detected in cells grown under reductive-dehalogenating
and pyruvate-fermenting conditions. An inducible, membrane-bound, periplasm-oriented formate
dehydrogenase was active only in cells grown with formate as electron donor; while, a
cytoplasmic formate dehydrogenase was detected in cells grown under reductive-dehalogenating
and pyruvate-fermenting conditions. Results from dehalogenation assays with D. tiedjei cell
suspensions suggest the membrane-bound reductive dehalogenaseis facing the cytoplasm . The
inducible cytochrome c, or the quinoid, alone or in combination, failed to replace reduced methyl
viologen as the electron donor for the reductive dehalogenase in vitro. The putative gene sequence
of the reductive dehalogenase small subunit was determined from inverse PCR products amplified
from genomic DNA, but the sequence did not have substantial similarity to any sequences in
GenBank. These data clearly demonstrate that D. tiedjei possesses elements necessary for
producing protons directly in the periplasm, generating a proton-motive force across the
cytoplasmic membrane. However, the data did not exclude the existence of additional
transmembrane proton translocation mechanisms, which would further enhance the proton-motive
force.
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Extent |
8514830 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-06-24
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0099356
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1998-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.