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Journal of Bacteriology, December 2001, p. 7076-7086, Vol. 183, No. 24
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

Bavesh D. Kana,1,2 Edward A. Weinstein,3 David Avarbock,3 Stephanie S. Dawes,1,2 Harvey Rubin,3,* and Valerie Mizrahi1,2,*

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 gamma -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.

Journal of Bacteriology, December 2001, p. 7076-7086, Vol. 183, No. 24
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.24.7076-7086.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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