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Journal of Bacteriology, December 2001, p. 7076-7086, Vol. 183, No. 24
MRC/SAIMR/WITS Molecular Mycobacteriology
Research Unit, South African Institute for Medical
Research,1 and Department of Molecular
Medicine and Hematology, School of Pathology, University of the
Witwatersrand,2 Johannesburg, South Africa, and
Division of Infectious Diseases, University of
Pennsylvania, Philadelphia, Pennsylvania3
Received 25 July 2001/Accepted 19 September 2001
The cydAB genes from Mycobacterium
smegmatis have been cloned and characterized. The
cydA and cydB genes encode the two
subunits of a cytochrome bd oxidase belonging to the
widely distributed family of quinol oxidases found in prokaryotes. The
cydD and cydC genes located immediately
downstream of cydB encode a putative ATP-binding
cassette-type transporter. At room temperature, reduced minus oxidized
difference spectra of membranes purified from wild-type M.
smegmatis displayed spectral features that are characteristic of the
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.24.7076-7086.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Characterization of the
cydAB-Encoded Cytochrome bd Oxidase from
Mycobacterium smegmatis
-proteobacterial type cytochrome bd oxidase.
Inactivation of cydA or cydB by insertion
of a kanamycin resistance marker resulted in loss of
d-heme absorbance at 631 nm. The d-heme
could be restored by transformation of the M. smegmatis
cyd mutants with a replicating plasmid carrying the highly
homologous cydABDC gene cluster from
Mycobacterium tuberculosis. Inactivation of cydA had no effect on the ability of M.
smegmatis to exit from stationary phase at 37 or 42°C. The
growth rate of the cydA mutant was tested under
oxystatic conditions. Although no discernible growth defect was
observed under moderately aerobic conditions (9.2 to 37.5 × 102 Pa of pO2 or 5 to 21% air saturation), the
mutant displayed a significant growth disadvantage when cocultured with
the wild type under extreme microaerophilia (0.8 to 1.7 × 102 Pa of pO2 or 0.5 to 1% air
saturation). These observations were in accordance with the two- to
threefold increase in cydAB gene expression observed
upon reduction of the pO2 of the growth medium from 21 to
0.5% air saturation and with the concomitant increase in
d-heme absorbance in spectra of membranes isolated from
wild-type M. smegmatis cultured at 1% air saturation.
Finally, the cydA mutant displayed a competitive growth
disadvantage in the presence of the terminal oxidase inhibitor,
cyanide, when cocultured with wild type at 21% air saturation in an
oxystat. In conjunction with these findings, our results suggest that
cytochrome bd is an important terminal oxidase in
M. smegmatis.
*
Corresponding author. Mailing address for Harvey Rubin:
University of Pennsylvania, 225 Johnson Pavilion, Philadelphia, PA 19104. Phone: (215) 662-6475. Fax: (215) 662-7842. E-mail:
rubinh{at}mail.med.upenn.edu..
Mailing address for Valerie Mizrahi: MRC/SAIMR/WITS Molecular Mycobacteriology Research Unit, SAIMR, P.O. Box 1038, Johannesburg 2000, South Africa. Phone: 2711-4899370. Fax: 2711-4899001. E-mail: 075val{at}chiron.wits.ac.za.
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