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Journal of Bacteriology, December 2001, p. 7017-7026, Vol. 183, No. 24
Department of Molecular Cell Physiology, Faculty of
Biology, BioCentrum Amsterdam, Free University, 1081 HV
Amsterdam,1 Department of Microbiology,
Wageningen University, 6703 CT Wageningen,2 and
Department of Mathematical Biochemistry, Swammerdam Institute
of Life Sciences, BioCentrum Amsterdam, University of Amsterdam, 1018 TV Amsterdam,3 The Netherlands, and
Biozentrum der Universitaet, D-60439 Frankfurt,
Germany4
Received 24 July 2001/Accepted 19 September 2001
Paracoccus denitrificans strains with mutations in
the genes encoding the cytochrome c550,
c552, or c1 and
in combinations of these genes were constructed, and their growth
characteristics were determined. Each mutant was able to grow
heterotrophically with succinate as the carbon and free-energy source,
although their specific growth rates and maximum cell numbers fell
variably behind those of the wild type. Maximum cell numbers and rates of growth were also reduced when these strains were grown with methylamine as the sole free-energy source, with the triple cytochrome c mutant failing to grow on this substrate. Under
anaerobic conditions in the presence of nitrate, none of the mutant
strains lacking the cytochrome bc1 complex
reduced nitrite, which is cytotoxic and accumulated in the medium. The
cytochrome c550-deficient mutant did
denitrify provided copper was present. The cytochrome
c552 mutation had no apparent effect on the
denitrifying potential of the mutant cells. The studies show that the
cytochromes c have multiple tasks in electron transfer.
The cytochrome bc1 complex is the electron
acceptor of the Q-pool and of amicyanin. It is also the electron donor
to cytochromes c550 and
c552 and to the cbb3-type oxidase. Cytochrome
c552 is an electron acceptor both of the
cytochrome bc1 complex and of amicyanin, as
well as a dedicated electron donor to the
aa3-type oxidase. Cytochrome
c550 can accept electrons from the
cytochrome bc1 complex and from amicyanin, whereas it is also the electron donor to both cytochrome
c oxidases and to at least the nitrite reductase during
denitrification. Deletion of the c-type cytochromes also
affected the concentrations of remaining cytochromes c,
suggesting that the organism is plastic in that it adjusts its
infrastructure in response to signals derived from changed electron
transfer routes.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.24.7017-7026.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Cytochromes c550,
c552, and c1 in
the Electron Transport Network of Paracoccus
denitrificans: Redundant or Subtly Different in
Function?
*
Corresponding author. Mailing address: Department of
Molecular Cell Physiology, Faculty of Biology, Free University, De
Boelelaan 1087, 1081 HV Amsterdam, The Netherlands. Phone:
31-20-4447179. Fax: 31-20-4447229. E-mail:
spanning{at}bio.vu.nl.
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