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Journal of Bacteriology, August 2000, p. 4557-4563, Vol. 182, No. 16
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

A Protease-Resistant Catalase, KatA, Released upon Cell Lysis during Stationary Phase Is Essential for Aerobic Survival of a Pseudomonas aeruginosa oxyR Mutant at Low Cell Densities

Daniel J. Hassett,1,* Eyad Alsabbagh,1 Kislay Parvatiyar,1 Michael L. Howell,2 Robert W. Wilmott,3 and Urs A. Ochsner4

Department of Molecular Genetics, Biochemistry and Microbiology1 and Division of Pulmonary Medicine, Allergy and Clinical Immunology, Department of Pediatrics,3 University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0524; Protein Express, Inc., Cincinnati, Ohio 452192; and Department of Microbiology, University of Colorado Health Sciences Center, Denver, Colorado 802624

Received 11 February 2000/Accepted 19 May 2000

A Pseudomonas aeruginosa oxyR mutant was dramatically sensitive to H2O2, despite possessing wild-type catalase activity. Oxygen-dependent oxyR phenotypes also included an inability to survive aerobic serial dilution in Luria broth and to resist aminoglycosides. Plating the oxyR mutant after serial dilution in its own spent culture supernatant, which contained the major catalase KatA, or under anaerobic conditions allowed for survival. KatA was resistant to sodium dodecyl sulfate, proteinase K, pepsin, trypsin, chymotrypsin and the neutrophil protease cathepsin G. When provided in trans and expressed constitutively, the OxyR-regulated genes katB, ahpB, and ahpCF could not restore both the serial dilution defect and H2O2 resistance; only oxyR itself could do so. The aerobic dilution defect could be complemented, in part, by only ahpB and ahpCF, suggesting that the latter gene products could possess a catalase-like activity. Aerobic Luria broth was found to generate ~1.2 µM H2O2 min-1 via autoxidation, a level sufficient to kill serially diluted oxyR and oxyR katA bacteria and explain the molecular mechanism behind the aerobic serial dilution defect. Taken together, our results indicate that inactivation of OxyR renders P. aeruginosa exquisitely sensitive to both H2O2 and aminoglycosides, which are clinically and environmentally important antimicrobials.

* Corresponding author. Mailing address: Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, 231 Bethesda Ave., Cincinnati, OH 45267-0524. Phone: (513) 558-1154. Fax: (513) 558-8474. E-mail: Daniel.Hassett{at}UC.Edu.

Journal of Bacteriology, August 2000, p. 4557-4563, Vol. 182, No. 16
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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